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Lymph node cells from preimmunized rabbits were cultured with varying concentrations of antigen in autologous serum which had been collected before immunization. [3H]Thymidine was added after 18 hours of culture and the cells were harvested at 24 or 66 hours for the determination of the radioactive labelling of acid-precipitable material. Preheating serum (56°, 20 minutes) enhanced labelling in both control and antigen-treated cultures. This 'heat effect' had an early (24 hour) non-specific component, independent of antigen concentration, and a late (66 hour) specific component which was most evident at high antigen concentrations. The conditions of preheating serum (temperature and time) required to produce the heat effect were similar to those required to remove haemolytic activity against rat erythrocytes. However, at certain temperatures and times there were discrepancies. These discrepancies, and data from experiments in which preheated and unheated sera were mixed in varying proportions, or interchanged in different sequences, were explicable on the basis of (i) a requirement for complement in stoichiometric quantities dependent on the number of cells being inhibited, (ii) the involvement of the majority of the cultured cells in the early non-specific component of the heat effect, but only cells capable of proliferating in response to added antigen in the late specific component, (iii) the secretion of complement by cultured cells. Preheating serum (66&deg:, 20 minutes) depressed labelling in control and antigentreated cultures and reduced agglutinating activity against both autologous and heterologous erythrocytes. The results are discussed in relationship to models which require that the size of a specific lymphocyte clone be positively or negatively regulated by the concentration of antigen specific for that clone. With increasing antigen concentration three effects on cells bearing specific receptor sites are distinguished. (i) Cell stimulation under conditions of antigen concentration and cell receptor specificity such that only a few antigen molecules can bind to cells. (ii) Complement-dependent inhibition under conditions such that more antigen molecules can bind to cells. (iii) Complement-independent inhibition under conditions, possibly unphysiological, such that very large quantities of antigen molecules can bind to cells. [ABSTRACT FROM AUTHOR]

Lymph node cells from immunized rabbits were cultured with varying concentrations of antigen in preheated (56°, 30 minutes) autologous serum which had been collected before immunization. [3H]Thymidine was present for the last 6 hours of the 24-hour culture period and the radioactive labelling of acid-precipitable material was then determined. Changes in labelling due to variations of culture conditions were interpreted according to whether they were specific for control or antigen-treated cultures or non-specific. Cell concentration and serum concentration were predominantly non-specific variables influencing the labelling in control and antigen-treated cultures to a proportionate extent. However, at serum concentrations below 5 per cent labelling was disproportionately inhibited in antigen-treated cultures; there were further minor disproportionate inhibitions at higher serum concentrations. Labelling was inhibited by increasing the concentration of serum from 25 to 50 per cent, mainly due to a non-diffusible competitive inhibitory activity. Isotope-dilution analysis of the effects of serum on labelling over a wide range of serum concentrations indicated that the relationship was a complex one with at least three step-wise stimulations of the maximum labelling rate being produced by increasing the serum concentrations from 0 to 25 per cent. Labelling in antigentreated cultures containing post-immunization serum was less than labelling in cultures containing an equal volume of preimmunization serum, but labelling in control cultures was enhanced by post-immunization serum. These results are shown to be compatible with the proposals (i) that labelling in control cultures reflects the response of cells to low concentrations of endogenous antigens, and (ii) that preimmunization serum and post-immunization serum contain ‘natural’ and ‘acquired’ antibodies respectively, which normally buffer cell-borne receptor sites against reaction with endogenous and exogenous antigens. [ABSTRACT FROM AUTHOR]

Certain foetal calf sera (FCS), upon initial injection, elicit delayed dermal reactions in some but not all guinea-pigs. The FCS that evoke significant dermal responses also initiate in vitro blastogenesis of lymphocytes taken from animals exhibiting the dermal reactions. A correlation exists between the severity of the in vivo reactions and the degree of blastogenesis observed. An explanation for these observations has been suggested, i.e. that some guineapigs possess spontaneously developed delayed hypersensitivity for antigen(s) contained in FCS. [ABSTRACT FROM AUTHOR]

The localization of HL-A histocompatibility antigens at the surface of human lymphocytes in electron microscopy has been studied using hybrid antibodies to bind electron-dense particles (ferritin and plant viruses) to anti-HL-A antibody. A discontinuous distribution of the markers is observed at the cell surface, which is identical with that described for H-2 antigens on mouse lymphocytes with the same technique. Double labelling experiments suggest that the areas of the cell surface where HL-A antigens are detected contain also the heterologous lymphocyte antigens detected by an anti-thymocyte serum and that HL-A antigens are not renewed at a detectable level during the period of the labelling procedure in the areas of the cell surface which are not labelled primarily with ferritin-anti-IgG-anti-HL-A complexes. The interpretation of the discontinuous labelling of HL-A antigens with direct immunoferritin techniques is discussed. [ABSTRACT FROM AUTHOR]

Human lymphocytes were fractionated on gradients of bovine serum albumin (BSA). Cells obtained from the more dense layers bound antigen specifically. Cells capable of interacting with antigen contained antibody which was separable with the nuclear components of the cell. Immune cells contained antibody which was specific for the immunizing antigen. Cell-bound antibody mediated and, in the presence of isologous antibody, slightly enhanced the uptake of antigen. Specific antibody passively bound to cell membranes did not promote uptake of antigen. Antigen which bound to lymphocytes in vitro was not enzymatically digested within the cell but became bound to acid-insoluble nuclear DNA. [ABSTRACT FROM AUTHOR]

The delayed-type iso-hypersensitivity that guinea-pigs acquire spontaneously towards a β-globulin antigen of other guinea-pigs has been measured in vitro. Serum containing the antigen specifically triggers lymphocytes from naturally iso-hypersensitive animals to undergo blastogenic response. This reaction is similar to that of lymphocytes cultured in the presence of antigen to which cell donors have been intentionally immunized. Thus, the in vitro technique of DNA synthesis may be used to detect both artificially induced and naturally occurring delayed-type hypersensitivities. In addition, naturally existing delayed hypersensitivity offers a plausible explanation for reports of spontaneous transformation of lymphocytes by homologous or heterologous serum and of certain other in vitro phenomena involving interaction of lymphoid cells from non-immunized donors. [ABSTRACT FROM AUTHOR]

Doses of 1·5 mg of prednisolone to newborn rats cause massive thymic involution and peripheral blood lymphocyte depletion without excessive mortality. By 3 weeks thymic mass, thymocytes and peripheral blood lymphocyte levels have all recovered fully, but antibody responsiveness to typhoid ‘H’ antigen is still depressed. As late as 10 weeks diminished levels of a serum immuno-globulin provisionally identified as IgA and depressed ‘H’ agglutinin titres are found in male but not in female treated rats. [ABSTRACT FROM AUTHOR]