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B cells have an important pathogenic role in the development of type 1 diabetes in the non-obese diabetic ( NOD) mouse. We have previously reported that NOD mice display an increased percentage of TACIhigh-expressing B cells compared with C57 BL/6 mice and this trait is linked to chromosomes 1 and 8. In this paper the genetic association of the transmembrane activator, calcium modulator and cyclophilin ligand interactor ( TACI) trait was confirmed using double congenic NOD. B6C1/Idd22 mice. TACI ligation by a proliferation-inducing ligand ( APRIL) has been shown to influence plasma cell differentiation, immunoglobulin production and isotype switch. Hence, the functional consequence of the up-regulation of TACI on NOD B cells was analysed both in vitro and in vivo. NOD B cells stimulated with APRIL showed an enhanced plasma cell differentiation and class switch to IgG and IgA compared with B cells from C57 BL/6 mice. Moreover, flow cytometry analyses revealed that germinal centre B cells in NOD failed to down-regulate TACI. Availability of the TACI ligand B-cell activating factor ( BAFF) has been shown to be a limiting factor in the germinal centre reaction. In line with this, upon immunization with 4-hydroxy-3-nitrophenylacetyl hapten-conjugated hen egg lysozyme, NOD mice produced higher titres of low-affinity antibodies compared with C57 BL/6 mice. This observation was supported by the detection of increased levels of BAFF in NOD germinal centres after immunization compared with C57 BL/6 by immunofluorescence. Our results support the hypothesis that increased TACI expression on NOD B cells contributes to the pathogenesis of type 1 diabetes in the NOD mouse. [ABSTRACT FROM AUTHOR]

As perhaps the staunchest advocates of repertoire purging as the central mechanism of immunological tolerance, we note with satisfaction a spate of recent, elegant papers which suggest an intrathymic clonal abortion model as the explanation for at least some examples of T-cell tolerance. This view agrees with the classical formulation of the Billingham-Brent-Medawar school of tolerance as a specific, central failure of immune responsiveness. Repertoire purging within the B-lymphocyte compartment remains much more controversial. There is no doubt that experimental models exist where the B cell is the reversible target of tolerance induction. The question is, in view of the ease of inducing autoantibody formation both in vivo and in vitro, just how relevant are such clonal anergy mechanisms to authentic self-tolerance? Arguments are presented that there must be two windows of tolerance susceptibility in the ontogeny of the B cell; one while it is maturing in the bone marrow, to prevent autoreactivity of high affinity to important accessible self-antigens; and a second soon after activation of pre-memory cells by exogenous antigen, to prevent fortuitous mutations towards high-affinity anti-self-reactivity establishing a forbidden clone. [ABSTRACT FROM AUTHOR]

A potent immunosuppressor factor, known as SER (suppressive E-receptor factor) has been identified in the body fluids of cancer patients. SER has been proven to be immunochemically analogous to the fetal form of haptoglobin. In this paper, we examine the role of SER immune suppressor in the immune surveillance mechanism of the host, using an affinity-purified SER. As shown in this study, SER, at µg/ml concentrations, inhibits the T-cell proliferation induced with either monoclonal or polyclonal T-cell activators in vitro in human, and also inhibits the primary antibody response to T-dependent antigens in vivo in mice. Likewise, SER also inhibits the immunoglobulin synthesis of human B lymphocytes induced by a B-cell mitogen, pokeweed mitogen, in the presence of a tumour promoter, phorbol myristate acetate (PMA). In contrast to the T-dependent antibody response in vivo in mice or T-dependent mitogen response in vitro in human, SER does not interfere with the T-independent antibody responses to DNP-Ficoll or TNP-LPS in mice. SER also interferes with the natural killer cell function of human peripheral blood mononuclear cells. Although SER inhibits the phagocytic functions of human peripheral neutrophils, it requires at least 10-20 times the concentration of SER present in normal human plasma. Since this concentration of SER is attainable in the sera of solid tumour-bearing patients, highly elevated levels of SER could predispose the patients to microbial infections as well. This study demonstrates that purified SER manifests multi-faceted down-regulatory effects on the defence mechanism of hosts, thereby it could compromise the patients' cell-mediated immunity in vivo. [ABSTRACT FROM AUTHOR]

Reagents for the identification of rabbit cell markers have been developed at a relatively slow rate. In this paper, rabbit cells are being characterized by polyclonal antibodies against a Tall antigen (RTLA), a B-cell antigen (RABELA) and an analogue of murine Ia antigen. A number of monoclonal antibodies, specific for lymphocytes and/or bone marrow and/or polymorphonuclear leucocytes, have been used for the analysis of cells with identifiable membrane antigens. Populations that have cells with two of the above antigens in the membranes were identified. To these ends, complement-mediated cell kill by antisera alone and in mixtures was employed. [ABSTRACT FROM AUTHOR]

This paper uses B-lymphocyte cloning methods to quantify the effects of anti-μ chain antibody on immature and mature B cells. Nude mouse spleen lymphocytes were incubated with various concentrations of sheep anti-mouse μ chain antibody for times varying from 10 min to 24 h. They were then washed and plated in the agar B-cell colony formation assay. Five to six days later, control B cells had developed into colonies with a plating efficiency of about 5%. B cells from newborn mice pretreated with anti-μ yielded fewer colonies. Remarkably low concentrations sufficed to inhibit subsequent mitogenesis. For example, 3 μg/ml acting for 1 h or 0.1 μg/ml acting for 24 h gave > 50% inhibition. Adult B cells were about thirty-fold more resistant to negative signalling. Immature cells became more profoundly inhibited as anti-μ treatment was prolonged. Anti-Ia or anti-H2 antibodies, in the absence of complement, did not deliver a negative signal. Anti-μ pretreatment also reduced the capacity of immature B cells to form clones of anti-hapten antibody-forming cells in a liquid microculture system where the triggering stimulus was a T-cell independent antigen. Mature 'T-independent' B cells were not inhibited. Populations of hapten-specific B cells prepared by the hapten-gelatin method were investigated in the agar cloning system. Pretreatment of immature cells with anti-μ reduced their capacity to form colonies, this subpopulation of cells behaving like unfractionated B cells. Furthermore, hapten--HGG delivered a negative signal also. Mature hapten-specific cells or unfractionated immature spleen cells formed normal numbers of colonies following hapten HGG treatment. Overall, the studies support the view that anti-μ antibody and hapten--HGG deliver strong negative signals to immature but not mature cells with appropriate receptors. The value of anti-μ as a model, universal tolerogen was supported. Fluorescence-activated cell sorter (FACS) analysis was performed to study the relationships between functional inhibition and Ig receptor modulation. We confirmed that the IgM receptors of immature B cells are more readily modulated by anti-μ antibody than those of mature cells. Furthermore, the receptor regeneration could be partially inhibited amongst immature but not mature B cells. There was not a close quantitative relationship between the degree of modulation and the degree of functional inhibition. The results did not support the view that irreversible receptor modulation as such was the cause of functional inhibition. [ABSTRACT FROM AUTHOR]

Examines various types of T lymphocyte functions in the spleens of mice infected four days previously with Friend virus (FV) in order to analyze its effect on the antibody response. Finding that infection does not reduce the percentage of T lymphocytes in the spleen, nor the ability to respond to phytohemagglutinin (PHA); Results suggesting that FV does not affect spleen T lymphocyte proliferation or helper function; Conclusion that the immune defect resides in the B lymphocytes.

For most antisera a linear relationship can be shown between log antigen concentration and the log concentration of antibody required to bind half the available antigen. This paper shows that the slope of this line, s, is related to the distribution of individual antibody clonotypes of different affinity. It is argued that the general form of the distribution approximates to exponential (rather than for example Gaussian) and that this indicates a requirement for some force to be exerted through the antigen-receptor bond in order to activate a B cell. An alternative parameter, A, which gives more weight to high affinity clonotypes, is offered in place of K0 as a measure of the avidity and biological effectiveness of an antiserum. [ABSTRACT FROM AUTHOR]

Mice infected with African trypanosomes produce exceptionally large amounts of serum IgM, a major part of which binds to non-trypanosome antigens such as trinitrophenol and single-strand DNA. In this paper, we describe that in cattle infected with Trypanosoma congolense and T. vivax, similar antibodies are found, although they bind mainly to protein antigens, such as β-galactosidase, ovalbumin and ferritin. The parasite non-specific IgM antibodies appear around the same time as the parasite-specific antibodies, but their origin and function are not clear. We tested the hypothesis that CD5+ B cells (or B-1 cells), which increase during trypanosome infections in cattle, are responsible for production of antibodies to non-trypanosome antigens. Splenic CD5+ and CD5- B cells from infected cattle were sorted and tested in a single cell blot assay. The numbers of immunoglobulin-secreting cells were similar in both B-cell populations. However, antibodies with reactivity for non-trypanosome antigens were significantly more prevalent in the CD5+ B-cell fraction and were exclusively IgM. The preference for production of these antibodies by CD5+ B cells and the expansion of this subpopulation during infections in cattle, strongly suggest that CD5+ B cells are the main source of trypanosome non-specific antibodies. We propose that these antibodies are natural, polyreactive antibodies that are predominantly secreted by CD5+ B cells. Since B-1 cells are up-regulated in many states of immune insufficiency, the immunosuppression associated with trypanosome infections may be responsible for the increase of this subset and the concomitant increase in trypanosome non-specific antibodies. [ABSTRACT FROM AUTHOR]

This study addresses itself to the problem of antibody formation in vitro by mouse splenic B lymphocytes enriched for reactivity to the hapten NIP by the hapten-gelatine binding and melting technique of Haas and Layton (1975). Small numbers of NIP-gelatine-bound B cells were placed in micro- cultures either by bulk dispensing of dilute cell suspensions, or by micromanipulation under direct microscopic visualization. Antibody formation was induced by the T cell-independent hapten-protein conjugate NIP-polymerized flagellin, using 104 thymus cells per microlitre as 'filler' cells. The frequency of precursors of NIP-specific antibody- forming cells among bound cells was about 2.2 × 10-2 (one cell in forty-five) by both statistical and direct evaluation, after adjustment for a background frequency of 6-10 × 10-8 precursors in the thymus filler cells. Single clones commenced antibody secretion asynchronously, as shown by the fact that the incidence of positive cultures continued to rise over the whole three days of culture, and that very small clones of one to four plaque-forming cells (PFC) were still found on day 3. The mean PFC number per positive culture rose from 1.2 at day 1 to 4.7 at day 2 and about 20 at day 3. Negative feedback, presumably mediated by antigen-antibody complexes, was shown to be a powerful effect in microcultures containing bound cells. It was evident with 250 cells per well (five clones) and the effect was progressive, such that with 10⊃ bound cells per well, plaque numbers were 40-50 per cent of their potential optimum; with 104, 10 per cent, and 105, 1 per cent. With routine techniques of harvesting of cultured cells, a failure to disperse PFC uniformly into single cells was noted. Groups of two or more large cells of very similar morphology were frequently observed at the centre of haemolytic plaques. Micromanipulation studies revealed that essentially all large cells at the centre of plaques were PFC. It was found that a routine plaque count underestimated the true PFC number per culture by a factor of 2. In the absence of negative feedback, the system is capable of generating one PFC per two input B lymphocytes. This is by far the most efficient plaque- generating system yet described, and contrasts with a yield of one PFC per 104 input cells in most typical tissue culture systems. Reasons for believing that both the culture and the enrichment systems can be further improved are discussed, and the potential of the method for understanding the cell and molecular biology of lymphocyte triggering is described. [ABSTRACT FROM AUTHOR]

In B cells, B-cell receptor (BCR) immunoglobulin revision is a common route for modifying unwanted antibody specificities via a mechanism called VH replacement. This in vivo process, mostly affecting heavy-chain rearrangement, involves the replacement of all or part of a previously rearranged IGHV gene with another germline IGHV gene located upstream. Two different mechanisms of IGHV replacement have been reported: type 1, involving the recombination activating genes complex and requiring a framework region 3 internal recombination signal; and type 2, involving an unidentified mechanism different from that of type 1. In the case of light-chain loci, BCR immunoglobulin editing ensures that a second V-J rearrangement occurs. This helps to maintain tolerance, by generating a novel BCR with a new antigenic specificity. We report that human B cells can, surprisingly, undergo type 2 replacement associated with κ light-chain rearrangements. The de novo IGKV- IGKJ products result from the partial replacement of a previously rearranged IGKV gene by a new germline IGKV gene, in-frame and without deletion or addition of nucleotides. There are wrcy/ rgyw motifs at the ' IGKV donor- IGKV recipient chimera junction' as described for type 2 IGHV replacement, but activation-induced cytidine deaminase ( AID) expression was not detected. This unusual mechanism of homologous recombination seems to be a variant of gene conversion-like recombination, which does not require AID. The recombination phenomenon described here provides new insight into immunoglobulin locus recombination and BCR immunoglobulin repertoire diversity. [ABSTRACT FROM AUTHOR]

Epstein-Barr virus ( EBV) infection may initiate production of autoantibodies and development of cancer and autoimmune diseases. Here we outline phenotypic and functional changes in B cells of patients with rheumatoid arthritis ( RA) related to EBV infection. The B-cell phenotype was analysed in blood and bone marrow ( BM) of RA patients who had EBV transcripts in BM ( EBV+, n = 13) and in EBV− ( n = 22) patients with RA. The functional effect of EBV was studied in the sorted CD25+ and CD25− peripheral B cells of RA patients ( n = 18) and healthy controls ( n = 9). Rituximab treatment results in enrichment of CD25+ B cells in peripheral blood ( PB) of EBV+ RA patients. The CD25+ B-cell subset displayed a more mature phenotype accumulating IgG-expressing cells. It was also enriched with CD27+ and CD95+ cells in PB and BM. EBV stimulation of the sorted CD25+ B cells in vitro induced a polyclonal IgG and IgM secretion in RA patients, while CD25+ B cells of healthy subjects did not respond to EBV stimulation. CD25+ B cells were enriched in PB and synovial fluid of RA patients. EBV infection affects the B-cell phenotype in RA patients by increasing the CD25+ subset and by inducing their immunoglobulin production. These findings clearly link CD25+ B cells to the EBV-dependent sequence of reactions in the pathogenesis of RA. [ABSTRACT FROM AUTHOR]

We have previously described two types of protective B-cell epitopes in the O-antigen ( OAg) of the Gram-negative bacterium Francisella tularensis: repeating internal epitopes targeted by the vast majority of anti- OAg monoclonal antibodies ( mAbs), and a non-overlapping epitope at the non-reducing end targeted by the previously unique IgG2a mAb FB11. We have now generated and characterized three mAbs specific for the non-reducing end of F. tularensis OAg, partially encoded by the same variable region germline genes, indicating that they target the same epitope. Like FB11, the new mAbs, Ab63 (Ig G3), N213 (Ig G3) and N62 (Ig G2b), had higher antigen-binding bivalent avidity than internally binding anti- OAg mAbs, and an oligosaccharide containing a single OAg repeat was sufficient for optimal inhibition of their antigen-binding. The X-ray crystal structure of N62 Fab showed that the antigen-binding site is lined mainly by aromatic amino acids that form a small cavity, which can accommodate no more than one and a third sugar residues, indicating that N62 binds mainly to the terminal Qui4 NFm residue at the nonreducing end of OAg. In efficacy studies with mice infected intranasally with the highly virulent F. tularensis strain Schu S4, N62, N213 and Ab63 prolonged survival and reduced blood bacterial burden. These results yield insights into how antibodies to non-reducing ends of microbial polysaccharides can contribute to immune protection despite the smaller size of their target epitopes compared with antibodies to internal polysaccharide regions. [ABSTRACT FROM AUTHOR]

Summary It is well established that the generation of a high-affinity long-lived antibody response requires the presence of T cells, specifically CD4+ T cells. These CD4+ T cells support the generation of a germinal centre (GC) response where somatic hypermutation and affinity maturation take place leading to the generation of memory B cells and plasma cells, which provide long-lasting protection. Greater insight into the nature of the CD4+ T cells involved in this process was provided by two studies in 2000 that described CD4+ T cells residing in the B cell follicle that expressed CXCR5. As a result these cells were named follicular B helper T cells, now more commonly known as T follicular helper (Tfh) cells. Since then there has been enormous growth in our understanding of these cells, now considered a distinct T helper (Th) cell lineage that can arise from naive CD4+ T cells following activation. This review summarizes some of the most recent work that has characterized Tfh cells and the pathways that lead to their generation. [ABSTRACT FROM AUTHOR]

Receptors for the Fc region of immunoglobulin G (FcγRs) are expressed on a broad range of haematopoietic cell types and are responsible for regulating antibody production and linking the humoral and effector responses. In response to a number of stimuli, such as cytokine signals or inflammation, FcγR expression at the cell surface is dynamically regulated. On B cells, we observed what appeared to be a correlation between CD22 expression and FcγRIIb expression when the latter was varied in a number of models. Further investigation revealed that this was specific to a particular anti-CD22 monoclonal antibody, which appeared to require stabilization by interaction with FcγRIIb for optimal binding to CD22. Since alterations in the regulation of FcγR expression are important in controlling immune responses and have been associated with a number of immune-mediated disease states, we suggest that it might be prudent to confirm the expression of cell surface markers by two independent methods. Furthermore, because the efficacy of therapeutic antibodies may depend upon their interaction with FcγRs, our results are relevant to their design and assessment. [ABSTRACT FROM AUTHOR]

The immune evasion mechanisms of pathogenic trypanosomatids involve a multitude of phenomena such as the polyclonal activation of lymphocytes, cytokine modulation and the enhanced detoxification of oxygen reactive species. A trypanothione cascade seems to be involved in the detoxification process. It was recently described and characterized a tryparedoxin ( LiTXN1) involved in Leishmania infantum cytoplasmatic hydroperoxide metabolism. LiTXN1 is a secreted protein that is up-regulated in the infectious form of the parasite, suggesting that it may play an important role during infection. In the present study, we investigated whether recombinant LiTXN1 (r LiTXN1) affects T- and B-cell functions in a murine model. We observed a significant increase in the CD69 surface marker on the B-cell population in total spleen cells and on isolated B cells from BALB/c mice after in vitro rLiTXN1 stimulus. Activated B-cells underwent further proliferation, as indicated by increased [3H]thymidine incorporation. Cytokine quantification showed a dose-dependent up-regulation of interleukin (IL)-10 secretion. B cells were identified as a source of this secretion. Furthermore, intraperitoneal injection of r LiTXN1 into BALB/c mice triggered the production of elevated levels of r LiTXN1-specific antibodies, predominantly of the immunoglobulin M (IgM), IgG1 and IgG3 isotypes, with a minimum reactivity against other heterologous antigens. Taken together, our data suggest that r LiTXN1 may participate in immunopathological processes by targeting B-cell effector functions, leading to IL-10 secretion and production of specific antibodies. [ABSTRACT FROM AUTHOR]

Synthetic anti-idiotypic antibodies represent a potentially valuable tool for the isolation and characterization of B cells that produce xenoantibodies. An anti-idiotypic antibody that binds to a subset of B cells producing antibodies encoded by the variable-region heavy chain 3 (VH3) germline genes DP35 [immunoglobulin variable-region heavy chain 3-11 (IGHV3-11)], DP-53 and DP-54 plus a small number of VH4 gene-encoded antibodies in humans has recently been identified. These germline progenitors also encode xenoantibodies in humans. We tested whether the small, clearly defined group of B cells identified with this anti-idiotypic antibody produce xenoantibodies in non-human primates mounting active immune responses to porcine xenografts. Peripheral blood B cells were sorted by flow cytometry on the basis of phenotype, and cDNA libraries were prepared from each of these sorted groups of cells. Immunoglobulin VH gene libraries were prepared from the sorted cells, and the VH genes expressed in each of the sorted groups were identified by nucleic acid sequencing. Our results indicate that xenoantibody-producing peripheral blood B cells, defined on the basis of binding to fluorescein isothiocyanate (FITC)-conjugated galactose α(1,3) galactose–bovine serum albumin (Gal-BSA) and the anti-idiotypic antibody 2G10, used the IGHV3-11 germline gene to encode xenoantibodies and were phenotypically CD11b+ (Mac-1+) and CD5–. This novel reagent may be used in numerous applications including definition of xenoantibody-producing B-cell subsets in humans and non-human primates and immunosuppression by depletion of B cells producing anti-Gal xenoantibodies. [ABSTRACT FROM AUTHOR]

Deficiencies in immune responses against polysaccharides can have direct consequences for patients, and therefore, a better undestanding of these immune reactions is crucial We have studied the immune response against the polysaccharide dextran B512 (Dx). Administration of immunogenic doses of thymus-independent (TI) Dx reduces the immunoglobulin G1 response to later challenges with a thymus-dependent (TD) form of Dx. We investigated if this suppression is a general phenomenon caused not only by Dx but also by other TI antigens, and examined possible mechanisms contributing to this unresponsiveness. We show that clonal exhaustion is not involved in modulating subsequent responses, nor is signalling via FcγRIIB or other antibody mediated pathways. The reduced TD response is not an exclusive Dx phenomenon; it is also induced by TI antigen oxazolone (Ox). However, responses against the hapten dinitrophenyl (DNP) are not affected, indicating that the TI priming negative effect is not a general process. This may be explained by the restricted immune response to both Dx and Ox, in contrast to the unrestricted DNP response. Our conclusion from these experiments is that the underlying mechanism for the TI-induced reduction of latter TD responses is a property of the TI activation itself. [ABSTRACT FROM AUTHOR]

Ligation of the antigen receptors on B cells transduces transmembrane signals leading to the induction of DNA synthesis. We now show that a pertussis toxin-sensitive heterotrimeric G-protein(s) of the Gi class plays a key role in the regulation of surface immunoglobulin (sIg)-mediated DNA synthesis in B cells. This site of G-protein regulation is distinct from that we have previously reported to govern the coupling of the antigen receptors on B cells to the phospholipase C-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate. We have, moreover, identified a candidate target for this new G-protein regulation by showing that mitogen-activating protein kinase (MAPkinase) activity, which plays a key role in the transduction of sIg-mediated proliferative signals in B cells, is abrogated by pre-exposure to pertussis toxin that covalently modifies and inactivates heterotrimeric G-proteins of the Gi class. Furthermore, our data suggest that this pertussis toxin-sensitive G-protein couples the antigen receptors to MAPkinase activation, at least in part, by regulating sIg-coupling to Lyn, Syk and perhaps Blk and Fyn activity, results consistent with studies in other systems which show that classical G-protein-coupled receptors recruit such protein tyrosine kinases to tranduce MAPkinase activation. Interestingly, however, this G-protein plays no apparent role in the control of up-regulation of major histocompatibility complex class II expression on B cells, suggesting that such G-protein-regulated-tyrosine kinase and MAPkinase activation is not required for the induction of this biological response following antigen receptor ligation. [ABSTRACT FROM AUTHOR]

A new bovine B-cell differentiation antigen is described that is detected by three monoclonal antibodies (mAb). The antigen is not an immunoglobulin and is precipitated from peripheral B cells as a molecule with an approximate molecular weight (MW) of 120,000 or 145,000 before and after reduction, respectively. Data obtained from two-colour cytofluorimetry and immunohistochemistry confirmed that the antigen was found only on mature B cells and on cells with dendritic morphology in the follicles of the organized lymphoid tissues. Its level of expression is directly correlated with that of IgM on peripheral blood B cells and Theileria parva-transformed B cells. The marker was also expressed on the peripheral cells which expressed surface IgG. Based on the antigen's cellular distribution, biochemistry and histochemistry, it is considered to be analogous to the human CD21 antigen. [ABSTRACT FROM AUTHOR]

CD5 (Ly-1) B cells are a minor subpopulation in mouse spleen and are thought to be responsible for the production of natural autoantibodies to bromelain-treated autologous erythrocytes (Br-RBC). Here it is shown that substantial numbers of conventional, CD5-negative, splenic B cells also secrete these antibodies in CBA and (NZB × NZW)F1 mice, whereas in NZB and BALB/c mice they are all produced by the CD5 B-cell population. However, stimulation with bacterial lipopolysaccharide in vivo preferentially activates the CD5 B-cell group to anti-Br-RBC antibody secretion. [ABSTRACT FROM AUTHOR]

Cationic particles interact by electrostatic forces with membrane components of diverse cell types, including lymphocytes. Contact with cationized streptococci was shown to induce a murine T-cell hybridoma to transcribe lymphokine mRNA as well as secrete interleukin-2. This activation was accompanied by a rise in intracellular calcium. Cationized streptococci-induced activation of this T-cell hybridoma could be specifically inhibited by either chelating extracellular calcium or by treating with CD4 monoclonal antibody. These data indicate that the in vitro behaviour of T cells can be modulated by charged microbial particles; such interactions may have relevance for chronic inflammation associated with some bacterial infections. [ABSTRACT FROM AUTHOR]

Human recombinant interleukin-4 (rIL-4) was assessed for its ability to promote the proliferative response of purified human B cells co-stimulated with submitogenic concentrations of soluble F(ab′)2 fragments of anti-immunoglobulin (Ig) antibodies. The growth-promoting activity of rIL-4 was usually as potent as, or even more potent than, that of recombinant interlcukin-2 (rIL-2), and more potent than that of recombinant interferon-gamma (rIFN-γ). Preincubation with rIL-4 did not cause enhancement of the proliferative response of B cells to the subsequent addition of rIL-4 and anti-IgM antibody. In contrast, the proliferative response of B cells preincubated with anti-IgM antibody and rIL-4 was potentiated by the subsequent addition of rIL-4. The simultaneous addition of rIFN-γ and rIL-2 or rIFN-γ, and rIL-4 had an additive effect in comparison with the response induced by rIL-2 or rIL-4 alone, respectively, whereas simultaneous addition of rIL-2 and rIL-4 induced a response equal or lower than that stimulated by rIL-2 or rIL-4 alone. The addition of rIFN-γ at the beginning of culture or preincubation of B cells with rIFN-γ and anti-IgM antibody potentiated the proliferative response of B cells to the subsequent addition of either rIL-2 or rIL-4. Taken together, these data suggest that rIL-4 acts as a growth factor for activated human B cells and displays on such cells a growth-promoting activity similar to that of rIL-2. [ABSTRACT FROM AUTHOR]

We have previously reported that the immunization of BALB/c mice with MOPC-104E myeloma protein (M104E) induced idiotype-sjjecific Ly 1-negative B lymphocytes that had an ability to enhance idiotype-,positive anti-dextran antibody production. It was also shown that the cell interaction between idiotypic and anti-idiotypic B lymphocytes was observed in a class Il-restricted manner. The effect of monoclonal anti-class II antibody on the B-B cell interaction is investigated in this report. The addition of anti-I-A or anti-I-E monoclonal antibody into the B-B cell interaction system, from both BALB/c (H-2d) and BALB.K (H-2k), inhibited the enhanced antibody production mediated by idiotype-immune B lymphocytes. Interestingly, however, it was revealed that the anti-IA and anti-I-E antibodies acted differently on each B-lymphocyte population. Pretreatment of an anti-idiotypic (idiotype-immune) enhancing B-lymphocyte population with anti-I-A antibody diminished its enhancing activity, while anti-I-E did not. On the other hand, pretreatment of dextranimmune antibody producing B cells with anti-I-A antibody showed no effect, while anti-I-E inhibited anti-dextran antibody production. When the enhancing B-lymphocyte population of F1 mice was treated with anti-I-A antibody specific for one of their parents' haplotypes, co-operation with the respective haplotype B cells was inhibited, but the other haplotype was not. The inhibitory effect of anti-class II antibodies could only be seen at the early phase of culture period. Taken together, the results of these experiments suggest that the class II antigens are concemed with the self-recognitive cell interaction among B lymphocytes in the frame of idiotype network systems. [ABSTRACT FROM AUTHOR]

Immunocytochemical identification of antibody-forming cells (AFCs) in situ was used to test the hypothesis that the maintenance of chronic allotype suppression in heterozygous rabbits is the result of an autoimmune B-cell-mediated response. Appreciable numbers of B cells with antibody activity directed against the suppressed allotypic determinant were found in spleen and bone marrow sections of all chronically suppressed rabbits examined. Appropriate double-staining was used to determine that such cells were of the non-suppressed allotype. These cells were indistinguishable from antiallotypic AFCs found in larger numbers in spleens of normal heterozygous rabbits that had been immunized against a heterologous allotypic determinant, Auto-anti-allotypic AFCs were not found in suppressed rabbits less than 8 weeks old, nor were they found in normal (non-suppressed) heterozygous rabbits or chimeric rabbits formed by the injection of histocompatible but allotype mismatched lymphoid cells at birth. The findings reported here support the hypothesis that the long term maintenance of allotype suppression in the rabbit may result from the suppressive activities of autoimmune B cells. It is suggested that the suppression of an allotype during the first few weeks of life could result in a loss of tolerance to a self-determinant. The kinetics of auto-anti-AFC production support this idea in showing that such cells are generated following the decline of the antibody used to induce suppression. The triggering event may be the emergence of B cells expressing the previously suppressed gene product. [ABSTRACT FROM AUTHOR]

Two distinct murine B-cell differentiation factors, designated B 151 -TRY 1 and B 151-TRF2, were described originally as B151 K12 T-cell hybridoma-derived lymphokines that induce immunoglobulin (Ig) secretion by antigen-activated B cells and unstimulated B cells, respectively. In the present study, we found that a highly purified B1 51-TRF1 fraction prepared by reversed-phase high-performance liquid chromatography (RP-H PLC) also has the ability to cause a polyclonal differentiation of unstimulated B cells into IgM-secreting cells in the apparent absence of co- stimulant. The activity of the B151-TRF1 fraction but not the B151-TRF2 fraction on unstimulated B cells was markedly inhibited by addition of a monoclonal antibody (mAb) specific for the B151- TRF 1/IL-S to the culture. To determine whether 8151 -TRF 1/IL-S and 8151 -TRF2 act on distinct populations among unstimulated B cells, the responsiveness of neonatal B cells and adult B cells that had been fractionated by Percoll density gradient centrifugation was assessed. B15 l-TRFI/IL-5 predominantly acted on lower density B cells, which appeared around 3 weeks after birth in the spleen. In contrast, B151-TRF2 could activate both lower and higher density B cells almost equally and B 151 -TRF2-responsive B cells were already present by 1 week of age. Thus, these results suggest that B151-TRFI/IL-5 and B151-TRF2 act on distinct subpopulations among antigen-unprimed normal B cells to induce IgM-secreting cells. [ABSTRACT FROM AUTHOR]

B6 mice heterozygous at the lpr locus (B6 +/lpr and B6 lpr/+) were compared with lpr homozygous mice (B6 lpr/lpr) and control mice (B6 +/+) for levels of serum immunoglobulin (Ig), presence of autoantibodies and rate of B-cell membrane immunoglobulin (mIg) capping. The total serum Ig levels in B6 +/lpr and B6 lpr/+ mice remained much below the high titres found in B6 lpr/lpr mice, and were close to the titres found in B6 +/+ mice. However, the presence of anti-single-stranded (ss) DNA antibodies and of anti-nuclear antibodies (ANA) was detected in most B6 +/lpr and B6 lpr/+ mice, although less frequently and in lower titres than in B6 lpr/lpr mice. The rate of mIg capping was higher in B6 +/lpr and B6 lpr/+ mice than in B6 +/+ mice, but the aceleration of the capping process remained inferior to the one found in B6 lpr/lpr mice. Therefore, the lpr locus is not totally recessive: some B-cell hyperactivity is expressed in the heterozygous state. This is in contrast with its lack of expression at the level of lympho-proliferation of the lpr-characteristic T-cell subset; none of the lpr heterozygous B6 mice displayed detectable lymphadenopathy. [ABSTRACT FROM AUTHOR]

Antibody production to influenza A strain virus X31 (H3N2) was measured in cultures of peripheral blood mononuclear cells (PBMC) stimulated with either antigen (X31) or pokeweed mitogen (PWM). With some donors, X31 antibody was produced in response to antigenic stimulation, but not as part of the polyclonal response to PWM, suggesting that antigen and PWM may be acting on different B-cell subpopulations. To test this hypothesis, T-cell depleted PBMC (E-) cells were fractionated on discontinuous Percoll gradients and assayed for antibody production in response to antigen or PWM. Fraction I (FrI = SC < 1.070) cultured in the presence of T cells responded well to PWM, but not at all to X31. FrII (1070 < SG < 1.075) and FrIII (SG > 1.075) cultured in the presence of T cells both responded well to X31, but only the medium-density B cells (FrII) were able to make specific antibody when T cells were replaced with T-cell replacing factor (TRF). Specific X31 antibody responses by medium- and high-density B cells (FrII and FrIII) were suppressed equally by the addition of allogeneic T-suppressor (Ts) cells. When allo-activated Ts cells were inactivated by irradiation, allogeneic T-helper (Th) cells were able to collaborate with both FrII and FrIII B cells in specific antibody responses to X31. Since TRF was not able to substitute for T cells in specific antibody responses by FrIII B cells, this result shows that allogeneic T-cell help was not mediated by non-specific 'allogeneic effect' factors and apparently requires cognate T cell-B cell interactions. [ABSTRACT FROM AUTHOR]

DBA/1 mice develop systemic polyarthritis and high titres of collagen autoantibodies after immunization with type II collagen. In this study we have analysed the frequency and specificity of antibody-producing B cells in draining lymph nodes 11 days after a primary immunization with rat type II collagen. A remarkably high frequency of type II collagen-reactive hybridomas (30%, n = 71), the majority cross-reacting with autologous type II collagen, were generated. Most of the collagen-reactive hybridomas produced IgG antibodies specific for type II collagen. Many other hybridomas produced multispecific antibodies (9%): these were preferentially of the IgM class. Some of the monoclonal multispecific hybridomas produced antibodies that cross-reacted with specific epitopes on the collagen molecule. One type II collagen-reactive hybridoma also displayed rheumatoid factor activity. Different mechanisms for the generation of the high frequency of collagen reactive antibodies are discussed. [ABSTRACT FROM AUTHOR]

Fifteen sera of patients with visceral leishmaniasis were investigated for the occurrence of autoantibodies. They were found in high incidence and titre, and with specificity to the intermediate filament (INFIL) proteins vimentin (12 out of 15 with a titre higher than 1 : 10) and keratin (9 out of 15 with a titre higher than 1 : 10) as well as to speckled anti-nuclear antigens (ANA). Additionally, supernatants of Leishmania major and Leishmania donovani cultures containing soluble parasite-derived antigens were mitogenic to cultures of mononuclear cells (MNC) obtained from healthy donors without specific antibodies to leishmanial antigens. The activation of MNC resulted in significant immunoglobulin production, some of which demonstrated autoantibody specificity to INFIL. The co-operation of monocytes, T cells and B cells was required in order to obtain maximal stimulation. The importance of polyclonal B-cell activation for the genesis and occurrence of autoantibodies in visceral leishmaniasis is discussed. [ABSTRACT FROM AUTHOR]

The effect of cyclosporin A (CyA) on the response of murine splenocytes to B-cell mitogens, TI-1 and 11-2 antigens was investigated. The proliferative response to LPS was found to be four- to five-fold less sensitive to inhibition than that to dextran sulphate. Antibody responses to a TI-2 antigen in vivo were suppressed by CyA treatment, whereas responses to the TI- 1 antigen DNP-LPS were markedly enhanced. Enhanced antibody responses to DNP-LPS were also demonstrable in vitro in the presence of CyA, and the enhancement was not removed by T-cell depletion. LPS-induced antibody production in vitro was enhanced at the same CyA concentrations that inhibited proliferation by 40-50%. The implications of these findings for the mechanism of action of CyA and for our understanding of B-cell differentiation are discussed. [ABSTRACT FROM AUTHOR]

The article focuses on the functional B-lymphocyte surface antigens. The differentiation of B cells is thought to be a multistep process involving a number of different signals. Although the number and physiological relevance of these signals are still controversial, surface immunoglobuling (IgG) is clearly not the sole surface molecule involved in this process. Earlier studies of functional human B-cell surface antigen relied on the use of antisera. The IgG and F(ab)2 fragment were found to induce thymidine incorporation in B cells. The optimal concentrations were very high and the methodology for B-cell stimulation was not given. Whether the effect is B-cell specific or not cannot be ascertained.

Non-T cells from tonsil or blood were fractionated according to buoyant density, isotype of surface immunoglobulin, or the ability to form rosettes with mouse erythrocytes. Each fraction was tested for the ability to proliferate in response to B. catarrhalis (Bc) and, for comparison, Staphylococcus aureus Cowan 1 (SAC) or an MLR supernatant (TF). Cells in all density fractions responded to Bc, the greatest response occurring in the high-density cell fraction. SAC could similarly induce proliferation in high-density cells, in contrast to TF which preferentially activated cells in the low-density fraction. When cells were fractionated by rosetting with mouse erythrocytes, both fractions (MRBC-R+ and MRBC-R-) responded to Be and to SAC, whereas the greatest response to TF occurred in the MRBC-R- cell fraction. Depletion of sIgD+ sIgM+ cells almost completely abolished the response to Bc, suggesting that responsive cells express both these classes of immunoglobulin on their membrane. Furthermore inclusion of anti-δ antibodies in cultures resulted in failure to proliferate in response to Bc. These data strongly suggest that Bc, like SAC but in contrast to TF, is able to stimulate proliferation in cells with the characteristics of resting B cells, i.e. high-density, sIgD+ cells which form rosettes with MRBC. This may be related to the fact that Bc, like SAC, is able to bind to human immunoglobulins. [ABSTRACT FROM AUTHOR]

Peripheral blood lymphocytes (PBL) from non-immunized rabbits or from rabbits immunized several months previously with a single dose of sheep red blood cells (SRRC) were cultured at several different cell densities in the presence of antigen for 5 days. The cells were then distributed in 10 μl microcultures at different cell densities to estimate the frequency of responding units. It was found that a shift up in cell concentration from first to second stage allows a more efficient expression of antibody-forming cell clones. We conclude that, during the first stage at low cell density, the precursor cells proliferate and, when they are partitioned in microcultures and the cell concentration is raised, maturation to antibody-forming cells occurs. This approach allows a separation of the proliferation event from the maturation event and it may prove to be a useful tool in the study of B-cell differentiation. [ABSTRACT FROM AUTHOR]

Antibodies to lipid A were raised in mice immunized with non-hydrolyzed Bordetella pertussis microorganisms, coated with lipid A isolated from the same bacteria. Anti-lipid A activity of immune sera was measured by radioimmunoassay. Four hybrid cell lines that secrete antibodies directed against the hydrophobic region of B. pertussis lipopolysaceha ride were produced by cell fusion between myeloma cells and spleen cells from immunized C3H/He-PAS mice. Differences were observed in the potency of the isolated monoclonal antibodies to inhibit B cell proliferation induced by lipopolysaccharide (LPS) or by lipid A, suggesting a selective recognition of effector sites present on the hydrophobic region of LPS. [ABSTRACT FROM AUTHOR]

Two types of experiment using local labelling of lymph nodes with FITC showed that lymphocytes emigrate from lymph nodes, predominantly in blood in the pig and in efferent lymph in the sheep. In the first type of experiment with the pig, few ceils emigrated via the lymph, while the number of labelled cells in the blood increased progressively and the indices in mesenteric blood were always higher than in jugular blood in simultaneously-drawn samples. However, in the sheep, when efferent lymph flowed freely, very low numbers emerged in blood and continuing large numbers of lymphocytes emerged in efferent lymph. In the second type of experiment carried out wholely under anaesthetic on mesenteric lymph nodes in pigs and sheep, and on superficial inguinal lymph nodes in pigs, the lymph node was isolated, the lymph and venous drainage collected and only the arterial supply maintained. Large numbers of FITC+ lymphocytes emigrated via the vein in pigs with either node cannulation (i.e. up to 7% blood iymphocytes were labelled with an emigration rate of ∼108 cells/hr) but in sheep, while lymph contained ∼30-80% labelled cells and the emigration rate was also ∼108 cells/hr, the mesenteric blood contained very few labelled cells (∼0.2%, giving a mean venous emigration rate of 2.7 × 106/hr). Study of the type of lymphocytes emerging from labelled pig lymph nodes and spleen during the phase of major emigration showed that sIg+ B and E rosette-forming T cells, but almost no Null cells, are involved. [ABSTRACT FROM AUTHOR]

We have compared the in vitro and in vivo mitogenic and polyclonal antibody (IgM-, IgG-, IgA- and anti-SRBC-secreting PFC) and autoantibody (IgM anti-ssDNA and anti-bromelin-treated mouse RBC-secreting PFC) responses to peptidogtycan (PG), LPS, protein A and PWM in homozygous xidor nu and normal mice. Our results demonstrated opposing effects of xid and nu on polyclonal B cell activation; in general, xid retarded and nu enhanced or did not change these responses. These effects, however, were greatly dependent on the in vitro or in vivo conditions of the stimulation and the type of polyclonal activator used and antibody assayed (isotype and specificity). In vitro, in xid mice, the numbers of all PFC assayed and proliferative responses were lower than in normal mice, whereas in nude mice the numbers of PFC were mostly unchanged, and proliferative responses were increased (PG, LPS) or decreased (protein A, PWM). The in vitro frequencies of autoantibody-secreting cells were similar (anti-DNA) in xid, nude and normal mice, or lower (anti-RBC) than normal in xid mice. In vivo, unstimulated xid mice had lower than normal numbers of IgM-, IgG- and autoantibody-secreting cells and higher numbers of IgA PFC, but in stimulated xid mice, the numbers of all Ig PFC were similar to normal, whereas anti-DNA and anti-RBC PFC were still depressed. The frequencies of anti-DNA and anti-RBC PFC were also lower than normal in xid mice in vivo. Nude mice in vivo had higher than normal numbers and frequencies of anti-DNA PFC and lower numbers of IgM and anti-SRBC PFC. These results indicate preferential retardation of autoantibody. secreting cells in xid mice in vivo and preferential enhancement of these cells in nude mice in vivo. Since in xid mice in vitro PG- and LPS-induced responses were similarly diminished, PG, like LPS, appears to primarily activate a late-maturing B cell subpopulation affected by the xid mutation. [ABSTRACT FROM AUTHOR]

In view of the controversial data in the literature regarding the in vitro IgE synthesis by human lymphocytes, the conditions for culture of lymphocytes and the methodology for measurement of the IgE produced are described in detail. In the absence of any added mitogen, enriched B cell preparations derived from 70% of allergic donors actively secreted 100 to 3200 pg/ml of IgE after culture for 7 days, at which time the cell viability was higher than 85%. In comparable B cell cultures derived from non-allergic donors, only trace amounts of de novo synthesized IgE were detected in 20% of the cases. All B cell cultures actively secreted IgG, IgA, IgM and there was no apparent relationship between the secretion of IgE and that of the other classes of Ig. By contrast, the synthesis of IgE by unfractionated peripheral blood mononuclear cells of allergic individuals, which were stimulated with pokeweed mitogen (PWM) under several experimental conditions, was not consistently reproducible, i.e. the spontaneous synthesis of IgE in such cultures was either suppressed or enhanced by PWM. The most important finding was that the secretion of IgE was selectively enhanced by supplementing the B cell cultures with cell-free supernatants (CFS) of cultures of neonatal lymphocytes which had been preincubated with 10 μg/ml IgE. It is, therefore, concluded that B cell cultures from allergic individuals constitute an appropriate model for investigations of the mechanisms underlying the regulation of human IgE synthesis. [ABSTRACT FROM AUTHOR]

This study compares the effects of passive administration of monoclonal anti-hapten (DNP) antibodies on primary plaque-forming cell (PFC) responses in mice to either soluble (DNP-keyhole limpet haemocyanin [KLH]) or paniculate (TNP-erythrocyte) antigens. IgM, IgG1, IgG2a and IgG2b antibodies at doses up to 500 μg induced at best a modest suppression of the IgM respond, and reproducibly enhanced the IgG response to DNP-KLH by up to 30-fold. In contrast, with the particulate antigen only the IgM antibody enhanced IgG PFC; IgG2 antibodies, and one out of two IgG1 antibodies caused marked suppression of the primary response to TNP-RBC. This required antibody with an intact Fc portion. The enhancement of IgG responses to soluble antigen presumably reflects rapid B cell priming by immune complexes trapped by follicular dendritic cells in lymphoid follicles, in agreement with earlier data. These results indicate that the nature of the antigen can markedly influence the immunoregulatory effects of antibodies on humoral responses. [ABSTRACT FROM AUTHOR]

Both B lymphocytes and cytotoxic T lymphocytes respond to signals from the T helper (Th) compartment, and such signals are mediated by a number of biochemically distinct factors. This raises the question whether help for B cells and T cells is a function of one or several different kinds of Th cell. Here we describe an in vitro and in vivo study of this problem, using a Th clone, designated MTH-1. The clone carries the cell surface markers Thy-1 and L3T4a, but lacks Lyt-2. It recognizes a minor alloantigen shared by DBA/2, B10.D2 and NZB spleen cells, and such recognition is restricted by H-2Ed. Recognition of antigen in vitro is accompanied by secretion of IL-2. In vivo, both primary and secondary CTL responses to multiple minor alloantigens are enhanced by small numbers (≤104) of MTH-1 cells. Recognition of alloantigen in a T-depleted B cell population results in the polyclonal activation and maturation of the B cells to secrete immunoglobulin; also, antigen-primed B ceils are augmented in their in vivo synthesis of specific antibody to the Thy-1·1 alloantigen by around 105 MTH-1 cells. Taken together, these results suggest a single Th clone can help both B cells and T cells. [ABSTRACT FROM AUTHOR]

Lectin-free supernatants obtained from PWM-stimulated lymphocytes, enable B cells to proliferate and secrete immunoglobulin. Both functions arc augmented by the addition of irradiated T cells. In the presence of antigen, these supernatants also enhance specific anti-tetanus toxoid antibody production. The components of the supernatant responsible for these activities have a molecular weight between 30,000 and 60,000, and have the characteristics of non-specific factors: they are genetically unrestricted, and do not bind to either antigen or anti-DR affinity columns. There is no evidence that the partial T dependency of these factors is an indication that their target is a T cell. Instead, T cells appear necessary to move the B cell into a state of activation in which it becomes responsive to the factor. Alternative activation signals such as Staph. A. Cowan can substitute for T cell help in the proliferative response, but not for immunoglobulin or antibody synthesis. The implications of these results for the approaches used to detect and classify B cell growth factors are discussed. [ABSTRACT FROM AUTHOR]

Mechanisms by which T and B lymphocytes co-operate in the in vitro secondary antibody response to trinitrophenyl-conjugated soluble protein antigens were investigated. The generation of antibody responses was analyzed when haptenic and carrier determinants were either linked or non-linked. Ability to co-operate through each of these mechanisms was influenced by the experimental conditions employed, particularly the mode of preparation of the T cells and the antigen concentration used. Nylon wool filtration of T cells may deplete a T helper population involved in non-linked recognition interactions.

A procedure is described for the in vivo removal of all detectable T lymphocytes from spleen and lymph nodes in mice. A single intraperitoneal injection of monoclonal anti-Thy-T antibody into mice leads to rapid depletion of functional I cells from peripheral lymphoid organs, but not thymus. The extent of T-celI depletion is dependent on the cytotoxic titre of the anti-Thy-I antibody used. Antibody with a median cytotoxic titre greater than 106 causes the complete removal of cells bearing Thy-I, Lyt-I and Lyt-2 surface antigens from peripheral lymphoid populations in 3 days. Eight days after treatment Thy-I +, Lyt-I + and Lyt-2+ cells begin to reappear in these organs. Splenic B cells, assayed by the expression of surface immunoglobulin (sig) and by mitogenic responsiveness to bacterial lipopolysaccharide (LPS), are not affected by this treatment. The monoclonal anti-Thy-i antibody does not appear to penetrate thymus tissue and bind to thymocytes. Anti-Thy-I antibody, but not F(ab')2, is required for in-vivo T-cell depletion. These findings indicate that anti-Thy-I antibody causes the removal of Thy-i + cells from peripheral lymphoid tissue, and as the circulating levels of anti-Thy-I antibody decrease, cells from the thymus repopulate the thymus-dependent areas of the depleted lymphoid organs. [ABSTRACT FROM AUTHOR]

Apart from a brief period after in-viva immunization, only a minority of human donors provide peripheral lymphocytes that synthesize specific antibody on stimulation with tetanus toxoid in vitro. A 20 μl hanging drop microculture technique using serum-free medium has been adapted to analyse the conditions under which B cells mature into antibody-secreting cells. Multiple permutations of antigen dose, cell concentration and T: B cell ratios have been examined. The results indicate that in-vitro failure of antigen response by the majority of donors is not due simply to an inappropriate choice of culture conditions. The addition to antigen-stimulated cultures of a lectin-free conditioned medium derived from pokeweed mitogen-stimulated peripheral lymphocytes, enables B cells from the majority of donors to produce high titres of specific antibody, in a T-dependent manner, for up to 24 months after immunization. The observed failure of prolonged antigen responsiveness in vitro thus appears to represent a failure to expand a population of antigen-specific B cells, rather than indicating an absence of such clones. [ABSTRACT FROM AUTHOR]

The influence of the thymus and the possible requirement for surface immunoglobulin expression for the development of K and NK activity were assessed in rats. This species was chosen in preference to mice as they show good levels of K-cell activity. Studies were carried out in athymic (rnu/rnu) rats some of which were treated from birth with rabbit anti-rat IgM antibody to suppress B-cell development. The results indicate that normal levels of both K and NK activity develop in the spleens of 6-8-week-old athymic rats, which do not contain cells expressing surface membrane immunoglobulin. While K and NK cells show characteristics of the lymphoid lineage, neither the thymus nor surface membrane immunoglobulin expression appears to be required for development of normal levels of these cytolytic activities. [ABSTRACT FROM AUTHOR]

Approximately half of the rosettes formed by rabbit Ig+ lymphocytes (B cells) and anti-Ig-coated erythrocytes or glutaraldehyde-fixed bacteria are dissociated upon the addition of rabbit serum. Rabbit serum was fractionated and the rosette-dissociating activity was found in purified preparations of rabbit α1- and α2-macroglobulins. Studies designed to elucidate the mechanism of rosette dissociation suggested that the α-macroglobulins dissociated rosettes by causing the release or proteolytic cleavage of the membrane proteins complexed with the anti-Ig-coated particles. These data suggest that the α-macroglobulins may have a role in the interaction of B lymphocytes with particulate antigens. [ABSTRACT FROM AUTHOR]

Unlike the suppression of a primary response to a thymus-dependent antigen, pretreatment of mice with anti-IgD serum has no effect on the response to a thymus-independent (TI) antigen. It has also been shown that anti-IgD serum injected parenterally into mice 2 days previously, has no suppressive effect on non-specific responsiveness to an intraperitoneal injection of LPS. There is a similar lack of effect on the non-specific element of responsiveness to a TI antigen. These results provide in vivo confirmation of the results of previous in vitro experimentation. [ABSTRACT FROM AUTHOR]

We have made a detailed investigation to determine which of the B-cell subsets could be stimulated by Staphylococcus aureus Cowan 1 bacterium (SpA CoI). B-cell subsets were separated from peripheral blood and tonsil lymphocytes by means of rosette formation with E, EAIgG, anti-immunoglobulin (Ig) conjugated ox erythrocytes (OE-anti-Ig), and Protein A conjugated OE (OE-Pro A) or by separation on a bovine serum albumin (BSA) discontinuous density gradient. The cells responding to SpA Col included E receptor negative (E-), C3 receptor positive (C3R+), and surface Ig positive (SIg+) B-cell subsets. Among these B-cell subsets, FcR- cells were more responsive than FcR+ cells. These B-cell subsets responded alone to SpA CoI and significantly proliferated, although they failed to respond alone to pokeweed mitogen (PWM) and Protein A of S. aureus (Protein A). Among the SIg+ B-cell subsets stimulated with SpA CoI, IgM+ and IgG+ B cells showed a marked response and IgA+, and IgD+ B cells showed much less response. Both Protein A receptor positive (Pro A · R+) and negative (Pro A · R-) cells responded well to SpA CoI. Fractionation of B cells on a BSA gradient revealed that comparatively small sized and denser B-cell subsets responded well to SpA CoI. From these criteria, it is suggested that B cells responding to SpA Col are capable of stimulating not only mature B cells, but can also stimulate immature B cells. [ABSTRACT FROM AUTHOR]

Inclusion of 14% Ficoll in the assay of rosette formation of human lymphocytes with mouse red blood cells (RBC) markedly enhances the cellular interaction. Both the strength of the rosettes (number of attached RBC) and the number of reacting lymphocytes are increased significantly, irrespective of the lymphocyte source—blood, lymph node and tonsil. In the presence of Ficoll, most of the sIg-bearing B lymphocytes [expressing receptors for Fc(IgG) and/or C3] and a significant number of the sheep RBC-rosetting T lymphocytes (particularly the nylon wool non-adherent subset from the tonsil), express receptors for the mouse erythrocyte. [ABSTRACT FROM AUTHOR]

In cellular immunology, peanut (Arachis hypogaea) lectin has been used to selectively agglutinate immature lymphoid cells and soybean (Glycine max) lectin to agglutinate B lymphocytes. We have used affinity chromatography to study the surface glycoproteins of rat and mouse lymphoid cells which bind to these lectins. Thymocyte and T and B lymphocyte glycoproteins were analysed either without modification (native) or after the removal of sialic acid with neuraminidase (asialo). The only native glycoprotein which was seen to bind to peanut lectin was the 95,000 mol. wt sialoglycoprorein from thymocytes. The equivalent molecule from T lymphocytes bound to peanut lectin only after neuraminidase digestion. Thus the selective agglutination of thymocytes by peanut lectin would seem to be due to a partial lack of sialic acid residues on the O-glycosidically-linked oligosaccharides of the thymocyte sialoglycoprotein. The B lymphocyte form of the leucocyte-common antigen was the only prominent native glycoprotein which was seen to bind to soybean lectin and this probably accounts for the specific binding of this lectin to B cells. The leucocyte-common antigens, in their asialo forms, from thymocytes and B and T lymphocytes differed in their binding to the lectins and this establishes that these glycoproteins which share antigenic determinants differ in their carbohydrate structures. [ABSTRACT FROM AUTHOR]

The regulation of pokeweed-mitogen (PWM) induced polyclonal immunoglobulin (Ig) production by suppressor T cells was investigated in mice. Generation of Ig-producing cells in PWM-stimulated culture was helped by T ceils and the helper activity was markedly augmented by X-irradiation, suggesting that the suppressor cells which may coexist in the helper source were abolished by X-irradiation. Present study also provided direct evidence for the involvement of suppressor cells in PWM-induced Ig production. Thus, suppressor cells could be induced by prestimulation of splenic T cells with high doses of PWM for 3–4 days. Both the precursor and effector suppressor T cells in this system were found to be Lyt 1-2+. It was further shown that although the Lyt 1-2+ subset could be directly stimulated by PWM to generate suppressor cells, the presence of Lyt 1+2- cells in the culture markedly enhanced the generation of Lyt 1-2+ suppressor cells. [ABSTRACT FROM AUTHOR]