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Pulmonary fibrosis involves various types of immune cells and soluble mediators, including TGF‐β and IL‐35, a recently identified heterodimeric cytokine that belongs to the IL‐12 cytokine family. However, the effect of regulatory IL‐35 may play an important role in fibrotic diseases. The aim of this paper is to explore the immunoregulatory role of IL‐35 in the development of fibrosis in interstitial lung disease (ILD). To gain a better understanding of this issue, the concentrations of IL‐35 and different profibrotic cytokines in fibrotic (F‐ILD) and non‐fibrotic (NF‐ILD) patients by ELISA were compared to that of intracellular IL‐35 and IL‐17 on CD4+ T cells stimulated in the presence of BAL or with different ratios of recombinant IL‐35 (rIL‐35) and TGF‐β (rTGF‐β), which were evaluated by flow cytometry. We observed that BAL concentration of IL‐35 was lower in F patients (p < 0.001) and was negatively correlated with concentrations of TGF‐β (p < 0.001) and IL‐17 (p < 0.001). In supplemented cell cultures, BAL from NF but not F patients enhanced the percentage of IL‐35 + CD4+ T (p < 0.001) cells and decreased the percentage of IL‐17 + CD4+ T cells (p < 0.001). The percentage of IL‐35 + CD4+ T cells correlated positively with BAL concentration of IL‐35 (p = 0.02), but correlated negatively with BAL concentrations of IL‐17 (p = 0.007) and TGF‐β (p = 0.01). After adjusting the concentrations of recombinant cytokines to establish a TGF‐β: IL‐35 ratio of 1:4, an enhanced percentage of IL‐35 + CD4+ T cells (p < 0.001) but a decreased percentage of IL‐17 + CD4+ T cells (p < 0.001) was observed. After adding recombinant IL‐35 to the BAL from F patients until a 1:4 ratio of TGF‐β: IL‐35 was reached, a significantly increased percentage of IL‐35 + CD4+ T cells (p < 0.001) and a decreased percentage of IL‐17 + CD4+ T cells (p = 0.003) was found. These results suggest that IL‐35 may induce an anti‐fibrotic response, regulating the effect of TGF‐β and the inflammatory response on CD4+ T cells. In addition, the TGF‐β: IL‐35 ratio in BAL has been shown to be a potential biomarker to predict the outcome of F patients with ILD. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cells provide an immediate first line of defence against viral infections. Memory responses, maintained by CD4+ T cells, require exposure to viral antigen and provide long-term protection against future infections. It is known that NK cells can promote the development of the adaptive response through cytokine production and cross-talk with antigen-presenting cells. In this paper however, we summarize a series of recent publications, in mouse models and for the first time in man, with the unifying message that rapid viral antigen control by the innate immune system limits antigen exposure to CD4+ cells thereby abrogating the development of a memory response. We discuss the significant implication of these studies on viral treatment strategies and immunization models. [ABSTRACT FROM AUTHOR]

Peripheral blood CD4 CD45RO T cells activated in vitro are able to induce expression of tumour necrosis factor-α (TNF-α) in monocytes via a contact-dependent mechanism. Activation is achieved either with interleukin-2 (IL-2)/IL-6/TNF-α over an 8-day period or cross-linking CD3 using anti-CD3 antibody for 48 hr. In this paper, we show that the p38 mitogen-activated protein kinase (MAPK) signalling pathway played different roles in the generation of effector function in these two types of activated T cells. In anti-CD3 activated T cells, p38 MAPK is a negative regulator for anti-CD3 induced cell proliferation and has no significant effect on the acquisition of either the effector function (induction of monocyte-derived TNF-α) or production of T-cell cytokines. In contrast, the p38 MAPK signalling pathway is required for the acquisition of cytokine-induced effector function and promotes cell proliferation and cytokine production. [ABSTRACT FROM AUTHOR]

This paper describes a model of successful immunotherapy of advanced lymphoma based on the selective elimination of cycling tumour-induced suppressor T cells. It shows that a single injection of the anti-mitotic drug, vinblasting (Vb), results in complete regression of a large L5178Y lymphoma and its metastases, but not if it is growing in an immunocompetent host. Vb-induced, immunologically mediated tumour regression was dependent on the anti-tumour function of CD8+ T cells, because regression was prevented by depleting the host of this subset of T cells 24 hr after Vb was given. Regression was also prevented by infusing the host with Vb-sensitive, CD4+ T cells from a turnout-bearing donor. These and other results are in keeping with the interpretation that Vbinduced regression of the L5178Y lymphoma depends on the ability of the drug to eliminate CD4+ suppressor T ceils that are replicating, and to spare non-replicating CD8+ effector cells, it is suggested that at an advanced stage of growth of the L5178Y lymphoma the host possesses an acquired population of antigen-primed CD8+ effector T cells that are unable to become activated in response to abundant tumour antigen because of the dominant influence of CD4+ suppressor cells. Activation of these CD8+ T cells was indicated by the finding that they were rapidly converted from being cyclophosphamide (Cy) resistant to being highly Cy sensitive within 48 hr of giving Vb. [ABSTRACT FROM AUTHOR]

The leucocyte common antigen, CD45 (T200, Ly-5), exists in a number of isoforms generated by differential usage of three exons that code for an extracellular region close to the NH2 terminus. Use of antibodies to different isoforms of CD45 has lead to the identification of two subsets of CD4+ T cells in rat, man and mouse. Data on the functions of the two rat CD4+ T-cell subsets isolated on the basis of different levels of expression of exon B (and/or C) are largely concordant with those obtained from the two subsets of human CD4 + T cells defined by their levels of expression of exon A. However, results presented in this paper on the CD45 phenotype of rat T cells that produce interferon-gamma (IFN-γ) are not compatible with the human data, if it is assumed that there are only two functional subsets of CD4+ T cells. The data could, in principle, be reconciled if the expression of exons A and B defined three rather than two subsets, and this possibility has now been examined in man where monoclonal antibodies against both A and B exon products are available. The results show the presence of a third CD4+ T-cell subset and that this extra subset is contained within the population originally shown to provide memory T-cell function. [ABSTRACT FROM AUTHOR]

Summary: Upon encounter with their cognate antigen, naive CD4 T cells become activated and are induced to differentiate into several possible T helper (Th) cell subsets. This differentiation depends on a number of factors including antigen‐presenting cells, cytokines and co‐stimulatory molecules. The strength of the T‐cell receptor (TCR) signal, related to the affinity of TCR for antigen and antigen dose, has emerged as a dominant factor in determining Th cell fate. Recent studies have revealed that TCR signals of high or low strength do not simply induce quantitatively different signals in the T cells, but rather qualitatively distinct pathways can be induced based on TCR signal strength. This review examines the recent literature in this area and highlights important new developments in our understanding of Th cell differentiation and TCR signal strength. [ABSTRACT FROM AUTHOR]

Summary: Although regulatory T‐cells (Tregs) have been shown to be expanded in acute dengue, their role in pathogenesis and their relationship to clinical disease severity and extent of viraemia have not been fully evaluated. The frequency of Tregs was assessed in 56 adult patients with acute dengue by determining the proportion of forkhead box protein 3 (FoxP3) expressing CD4+ CD25+T‐cells (FoxP3+ cells). Dengue virus (DENV) viral loads were measured by quantitative real‐time polymerase chain reaction (PCR) and DENV‐specific T‐cell responses were measured by ex‐vivo interferon (IFN)‐γ enzyme‐linked immunospot (ELISPOT) assays to overlapping peptide pools of DENV‐NS3, NS1 and NS5. CD45RA and CCR4 were used to phenotype different subsets of T‐cells and their suppressive potential was assessed by their expression of cytotoxic T lymphocyte‐antigen 4 (CTLA‐4) and Fas. While the frequency of FoxP3+ cells in patients was significantly higher (P < 0·0001) when compared to healthy individuals, they did not show any relationship with clinical disease severity or the degree of viraemia. The frequency of FoxP3+ cells did not correlate with either ex‐vivo IFN‐γ DENV‐NS3‐, NS5‐ or NS1‐specific T‐cell responses. FoxP3+ cells of patients with acute dengue were predominantly CD45RA+ FoxP3low, followed by CD45RA‐FoxP3low, with only a small proportion of FoxP3+ cells being of the highly suppressive effector Treg subtype. Expression of CCR4 was also low in the majority of T‐cells, with only CCR4 only being expressed at high levels in the effector Treg population. Therefore, although FoxP3+ cells are expanded in acute dengue, they predominantly consist of naive Tregs, with poor suppressive capacity. [ABSTRACT FROM AUTHOR]

CD4 T cells help immune responses, but knowledge of how memory CD4 T cells are regulated and how they regulate adaptive immune responses and induce immunopathology is limited. Using adoptive transfer of virus-specific CD4 T cells, we show that naive CD4 T cells undergo substantial expansion following infection, but can induce lethal T helper type 1-driven inflammation. In contrast, memory CD4 T cells exhibit a biased proliferation of T follicular helper cell subsets and were able to improve adaptive immune responses in the context of minimal tissue damage. Our analyses revealed that type I interferon regulates the expansion of primary CD4 T cells, but does not seem to play a critical role in regulating the expansion of secondary CD4 T cells. Strikingly, blockade of type I interferon abrogated lethal inflammation by primary CD4 T cells following viral infection, despite that this treatment increased the numbers of primary CD4 T-cell responses. Altogether, these data demonstrate important aspects of how primary and secondary CD4 T cells are regulated in vivo, and how they contribute to immune protection and immunopathology. These findings are important for rational vaccine design and for improving adoptive T-cell therapies against persistent antigens. [ABSTRACT FROM AUTHOR]

Induction of tolerance is a key mechanism to maintain or to restore immunological homeostasis. Here we show that Foxp3+ regulatory T (Treg) cells use Dickkopf-1 ( DKK-1) to regulate T-cell-mediated tolerance in the T-cell-mediated autoimmune colitis model. Treg cells from DKK-1 hypomorphic doubleridge mice failed to control CD4+ T-cell proliferation, resulting in CD4 T-cell-mediated autoimmune colitis. Thymus-derived Treg cells showed a robust expression of DKK-1 but not in naive or effector CD4 T cells. DKK-1 expression in Foxp3+ Treg cells was further increased upon T-cell receptor stimulation in vitro and in vivo. Interestingly, Foxp3+ Treg cells expressed DKK-1 in the cell membrane and the functional inhibition of DKK-1 using DKK-1 monoclonal antibody abrogated the suppressor function of Foxp3+ Treg cells. DKK-1 expression was dependent on de novo protein synthesis and regulated by the mitogen-activated protein kinase pathway but not by the canonical Wnt pathway. Taken together, our results highlight membrane-bound DKK-1 as a novel Treg-derived mediator to maintain immunological tolerance in T-cell-mediated autoimmune colitis. [ABSTRACT FROM AUTHOR]

Several host factors have been implicated in resistance to HIV infection in individuals who remain HIV-seronegative despite exposure. In a cohort of HIV-serodiscordant heterosexual couples, we investigated interactions between systemic inflammation and T-cell activation in resistance to HIV infection. Males and females in stable long-term relationships with either HIV-infected or uninfected partners were recruited, blood T-cell activation ( CD38, HLA- DR, CCR5 and Ki67) and plasma cytokine concentrations were evaluated. The HIV-negative exposed individuals had significantly lower frequencies of CCR5+ CD4+ and CD8+ T cells than unexposed individuals. Mean fluorescence intensity of CCR5 expression on CD4+ T cells was significantly lower in HIV-negative exposed than unexposed individuals. Protective CCR5 haplotypes ( HHA/ HHF*2, HHF*2/ HHF*2, HHC/ HHF*2, HHA/ HHA, HHA/ HHC and HHA/ HHD) tended to be over-represented in exposed compared with unexposed individuals (38% versus 28%, P = 0·58) whereas deleterious genotypes ( HHC/ HHD, HHC/ HHE, HHD/ HHE, HHD/ HHD and HHE/ HHE) were under-represented (26% versus 44%; P = 0·16). Plasma concentrations of interleukin-2 ( P = 0·02), interferon- γ ( P = 0·05) and granulocyte-macrophage colony-stimulating factor ( P = 0·006) were lower in exposed compared with unexposed individuals. Activation marker expression and systemic cytokine concentrations were not influenced by gender. We conclude that the dominant signature of resistance to HIV infection in this cohort of exposed but uninfected individuals was lower T-cell CCR5 expression and plasma cytokine concentrations. [ABSTRACT FROM AUTHOR]

Adoptive cell immunotherapy for human diseases, including the use of T cells modified to express an anti-tumour T-cell receptor ( TCR) or chimeric antigen receptor, is showing promise as an effective treatment modality. Further advances would be accelerated by the availability of a mouse model that would permit human T-cell engineering protocols and proposed genetic modifications to be evaluated in vivo. NOD- scid IL2rγ null ( NSG) mice accept the engraftment of mature human T cells; however, long-term evaluation of transferred cells has been hampered by the xenogeneic graft-versus-host disease ( GVHD) that occurs soon after cell transfer. We modified human primary CD4+ T cells by lentiviral transduction to express a human TCR that recognizes a pancreatic beta cell-derived peptide in the context of HLA- DR4. The TCR-transduced cells were transferred to NSG mice engineered to express HLA- DR4 and to be deficient for murine class II MHC molecules. CD4+ T-cell-depleted peripheral blood mononuclear cells were also transferred to facilitate engraftment. The transduced cells exhibited long-term survival (up to 3 months post-transfer) and lethal GVHD was not observed. This favourable outcome was dependent upon the pre-transfer T-cell transduction and culture conditions, which influenced both the kinetics of engraftment and the development of GVHD. This approach should now permit human T-cell transduction protocols and genetic modifications to be evaluated in vivo, and it should also facilitate the development of human disease models that incorporate human T cells. [ABSTRACT FROM AUTHOR]

The immune system is composed of a variety of cells that act in a coordinated fashion to protect the organism against a multitude of different pathogens. The great variability of existing pathogens corresponds to a similar high heterogeneity of the immune cells. The study of individual immune cells, the fundamental unit of immunity, has recently transformed from a qualitative microscopic imaging to a nearly complete quantitative transcriptomic analysis. This shift has been driven by the rapid development of multiple single-cell technologies. These new advances are expected to boost the detection of less frequent cell types and transient or intermediate cell states. They will highlight the individuality of each single cell and greatly expand the resolution of current available classifications and differentiation trajectories. In this review we discuss the recent advancement and application of single-cell technologies, their limitations and future applications to study the immune system. [ABSTRACT FROM AUTHOR]

Indoleamine 2,3-dioxygenase ( IDO) is expressed in antigen-presenting cells and exerts immunosuppressive effects on CD4+ T cells. One mechanism is through the inhibition of aerobic glycolysis. Another prerequisite for T-cell proliferation and differentiation into effector cells is increased fatty acid ( FA) synthesis. The effect of IDO on enzymes involved in FA synthesis was evaluated in primary human cells both in mixed lymphocyte reactions in the presence or not of the IDO inhibitor 1- dl-methyl-tryptophan, and in stimulated CD4+ T cells in the presence or not of the general control non-derepressible 2 ( GCN2) kinase activator tryptophanol ( TRP). IDO or TRP inhibited cell proliferation. By assessing the level of GCN2 kinase or mammalian target of rapamycin complex 1 substrates along with a kynurenine free system we showed that IDO exerts its effect mainly through activation of GCN2 kinase. IDO or TRP down-regulated ATP-citrate lyase and acetyl coenzyme A carboxylase 1, key enzymes involved in FA synthesis. Also, IDO or TRP altered the expression of enzymes that control the availability of carbon atoms for FA synthesis, such as lactate dehydrogenase-A, pyruvate dehydrogenase, glutaminase 1 and glutaminase 2, in a way that inhibits FA synthesis. In conclusion, IDO through GCN2 kinase activation inhibits CD4+ T-cell proliferation and down-regulates key enzymes that directly or indirectly promote FA synthesis, a prerequisite for CD4+ T-cell proliferation and differentiation into effector cell lineages. [ABSTRACT FROM AUTHOR]

Targeting of antigens to the endocytic uptake receptor DEC205 resulted in enhanced antigen presentation by dendritic cells ( DCs). In combination with adjuvants for DC maturation, proteins coupled to an antibody against DEC205 induced strong pathogen-specific immune responses, whereas without additional adjuvant tolerance could be induced. As less is known about DNA vaccines encoding DEC205-targeted antigens, we explored the immunogenicity and efficacy of a dendritic cell-targeted DNA vaccine against influenza A virus ( IAV) delivered by electroporation. Although coupling of haemagglutinin to a single-chain antibody against DEC205 enhanced antigen presentation on MHC class II and activation of T-cell receptor-transgenic CD4 T cells, the T-cell responses induced by the targeted DNA vaccine in wild-type BALB/c mice were significantly reduced compared with DNA encoding non-targeted antigens. Consistently, these mice were less protected against an IAV infection. Adoptive transfer experiments were performed to assess the fate of the antigen-specific T cells in animals vaccinated with DNA encoding DEC205-targeted antigens. By this, we could exclude the general deletion of antigen-specific T cells as cause for the reduced efficacy, but observed a local expansion of antigen-specific regulatory T cells, which could suppress the activation of effector cells. In conclusion, DNA vaccines encoding DEC205-targeted antigens induce peripheral tolerance rather than immunity in our study. Finally, we evaluated our DNA vaccines as prophylactic or therapeutic treatment in an allergen-induced asthma mouse model. [ABSTRACT FROM AUTHOR]

Basophils are known to modulate the phenotype of CD4+ T cells and to enhance T helper type 2 responses in vitro and in vivo. In this study, we demonstrate that murine basophils inhibit proliferation of CD4+ T cells in autologous and allogeneic mixed lymphocyte reactions. The inhibition is independent of Fas and MHC class II, but dependent on activation of basophils with subsequent release of interleukin-4 ( IL-4) and IL-6. The inhibitory effect of basophils on T-cell proliferation can be blocked with antibodies against IL-4 and IL-6 and is absent in IL-4/ IL-6 double-deficient mice. In addition, we show that basophils and IL-4 have beneficial effects on disease activity in a murine model of acute graft-versus-host disease (Gv HD). When basophils were depleted with the antibody MAR-1 before induction of Gv HD, weight loss, Gv HD score, mortality and plasma tumour necrosis factor levels were increased while injection of IL-4 improved Gv HD. Basophil-depleted mice with Gv HD also have increased numbers of CD4+ T cells in the mesenteric lymph nodes. Our data show for the first time that basophils suppress autologous and allogeneic CD4+ T-cell proliferation in an IL-4-dependent manner. [ABSTRACT FROM AUTHOR]

The frequency of CD4+ Foxp3+ regulatory T (Treg) cells is often significantly increased in the blood of tumour-bearing mice and people with cancer. Moreover, Treg cell frequencies are often higher in tumours compared with blood and lymphoid organs. We wished to determine whether certain chemokines expressed within the tumour mass selectively recruit Treg cells, thereby contributing to their enrichment within the tumour-infiltrating lymphocyte pool. To achieve this goal, the chemokine profile of carcinogen-induced fibrosarcomas was determined, and the chemokine receptor expression profiles of both CD4+ Foxp3− and CD4+ Foxp3+ T cells were compared. These analyses revealed that the tumours are characterized by expression of inflammatory chemokines ( CCL2, CCL5, CCL7, CCL8, CCL12, CXCL9, CXCL10 and CX3 CL1), reflected by an enrichment of activated Foxp3− and Foxp3+ T cells expressing T helper type 1-associated chemokine receptors. Notably, we found that CXCR3+ T cells were significantly enriched in the tumours although curiously we found no evidence that CXCR3 was required for their recruitment. Instead, CXCR3 marks a population of activated Foxp3− and Foxp3+ T cells, which use multiple and overlapping ligand receptor pairs to guide their migration to tumours. Collectively, these data indicate that enrichment of Foxp3+ cells in tumours characterized by expression of inflammatory chemokines, does not occur via a distinct chemokine axis, thus selective chemokine blockade is unlikely to represent a meaningful therapeutic strategy for preventing Treg cell accumulation in tumours. [ABSTRACT FROM AUTHOR]

There is a progressive increase in cardiovascular disease with declining renal function, unexplained by traditional risk factors. A CD4+ T-cell subpopulation ( CD4+ CD28−), activated by human heat-shock protein 60 ( hHSP 60), expands in patients with acute coronary syndrome and is associated with vascular damage. These cells exhibit cytotoxicity via expression of activating killer cell-immunoglobulin-like receptor KIR2 DS2, mainly in the absence of inhibitory KIR2 DL3. We investigated expansion of these cells and the pathogenic role of the KIR in non-dialysis-dependent chronic kidney disease ( NDD- CKD) and end-stage haemodialysis-dependent renal disease ( HD- ESRD) patients. CD4+ CD28− cells were present in 27% of the NDD- CKD and HD- ESRD patients (8-11% and 10-11% of CD4+ compartment, respectively). CD4+ CD28− cells were phenotyped for KIR and DAP12 expression. Cytotoxicity was assessed by perforin and pro-inflammatory function by interferon- γ expression on CD4+ CD28− clones ( NDD- CKD n = 97, HD- ESRD n = 262). Thirty-four per cent of the CD4+ CD28− cells from NDD- CKD expressed KIR2 DS2 compared with 56% in HD- ESRD patients ( P = 0·03). However, 20% of clones expressed KIR2 DL3 in NDD- CKD compared with 7% in HD- ESRD patients ( P = 0·004). DAP12 expression in CD28− 2 DS2+ clones was more prevalent in HD- ESRD than NDD- CKD (92% versus 60%; P < 0·001). Only 2 DS2+ 2 DL3− DAP12+ clones were cytotoxic in response to hHSP 60. CD4+ CD28− cells exhibited increased KIR2 DS2, reduced KIR2 DL3 and increased DAP12 expression in HD- ESRD compared with NDD- CKD patients. These findings suggest a gradual loss of expression, functionality and protective role of inhibitory KIR2 DL3 as well as increased cytotoxic potential of CD4+ C28− cells with progressive renal impairment. Clonal expansion of these T cells may contribute to heightened cardiovascular events in HD-ESRD. [ABSTRACT FROM AUTHOR]

Tumour progression is associated with immune-suppressive conditions that facilitate the escape of tumour cells from the regimen of immune cells, subsequently paralysing the host defence mechanisms. Induction of CD4+ CD25+ FoxP3+ T regulatory (Treg) cells has been implicated in the tumour immune escape mechanism, although the novel anti-cancer treatment strategies targeting Treg cells remain unknown. The focus of this study is to define the interaction between tumour and immune system, i.e. how immune tolerance starts and gradually leads to the induction of adaptive Treg cells in the tumour microenvironment. Our study identified hyperactivated mitogen-activated protein kinase kinase ( MEK)/extracellular signal-regulated kinase ( ERK) -signalling as a potential target for reversing Treg cell augmentation in breast cancer patients. In more mechanistic detail, pharmacological inhibitors of MEK/ ERK signalling inhibited transforming growth factor- β ( TGF- β) production in tumour cells that essentially blocked TGF- β- SMAD3/ SMAD4-mediated induction of CD25/interleukin-2 receptor α on CD4+ T-cell surface. As a result high-affinity binding of interleukin-2 on those cells was prohibited, causing lack of Janus kinase 1 ( JAK1)/ JAK3-mediated signal transducer and activator of transcription 3 ( STAT3)/ STAT5 activation required for FoxP3 expression. Finally, for a more radical approach towards a safe MEK inhibitor, we validate the potential of multi-kinase inhibitor curcumin, especially the nano-curcumin made out of pure curcumin with greater bioavailability; in repealing tumour-shed TGF- β-induced Treg cell augmentation. [ABSTRACT FROM AUTHOR]

Wolbachia is an endosymbiotic bacterium of the filarial nematode Brugia malayi. The symbiotic relationship between Wolbachia and its filarial host is dependent on interactions between the proteins of both organisms. However, little is known about Wolbachia proteins that are involved in the inflammatory pathology of the host during lymphatic filariasis. In the present study, we cloned, expressed and purified Wolbachia surface protein (r-wsp) from Wolbachia and administered it to mice, either alone or in combination with infective larvae of B. malayi (Bm-L3) and monitored the developing immune response in infected animals. Our results show that spleens and mesenteric lymph nodes of mice immunized with either r-wsp or infected with Bm-L3 show increased percentages of CD4+ T helper type 17 (Th17) cells and Th1 cytokines like interferon- γ and interleukin-2 (IL-2) along with decreased percentages of regulatory T cells, Th2 cytokines like IL-4 and IL-10 and transforming growth factor β (TGF- β) levels in culture supernatants of splenocytes. These observations were stronger in mice immunized with r-wsp alone. Interestingly, when mice were first immunized with r-wsp and subsequently infected with Bm-L3, percentages of CD4+ Th17 cells and Th1 cytokines increased even further while that of regulatory T cells, Th2 cytokines and TGF- β levels decreased. These results for the first time show that r-wsp acts synergistically with Bm-L3 in promoting a pro-inflammatory response by increasing Th17 cells and at the same time diminishes host immunological tolerance by decreasing regulatory T cells and TGF- β secretion. [ABSTRACT FROM AUTHOR]

Soluble MHCII (sMHCII) molecules are present in body fluids of healthy individuals and are considered to be involved in the maintenance of self tolerance, and are also related to various diseases. Their concentration increases during in vivo antigen-specific tolerogenic stimulation and it was recently shown that exosome-mediated tolerance is MHCII dependent. At the cellular level, sMHCII proteins compete with membrane MHCII for T-cell receptor binding on CD4+ T cells. Immunoaffinity purification techniques isolated sMHCII antigens from the serum of human serum albumin (HSA) -tolerant mice as a single highly glycosylated protein of ~ 60 000 molecular weight, specifically interacting with anti-class II antibodies in Western blotting and ELISA. Mass spectroscopy showed that these sMHCII proteins were loaded with the tolerogenic peptide as well as multiple self peptides. At the cellular level, sMHCII suppressed antigen-specific, and to a lesser degree antigen-non-specific, spleen cell proliferation and induced CD25 in naive T cells. In T cells activated by antigen-seeded macrophages, sMHCII decreased CD28 and increased CTLA-4 protein expression, while decreasing interleukin-2 and increasing interleukin-10 production. In this case, sMHCII proteins were shown to decrease ZAP-70 and LAT phosphorylation. The results presented here for the first time provide evidence for the role of sMHCII proteins in immune response suppression and maintenance of tolerance, revealing novel regulatory mechanisms for immune system manipulation. [ABSTRACT FROM AUTHOR]

Human enterovirus 71 ( EV71) is one of the major causes of hand, foot and mouth disease ( HFMD), which leads to significant mortality in infected children. A prophylactic vaccine is urgently needed. However, little is known about the protective T-cell immunity in individuals infected with the EV71 virus. In this study, we performed a comprehensive ex vivo interferon- γ ELISPOT analysis in 31 children infected with EV71 as well as in 40 healthy adult controls of the CD4+ and CD8+ T-cell responses to overlapping peptides spanning the VP1 structural protein and RNA-dependent RNA polymerase (RdRp) non-structural protein. EV71-specific CD4 T-cell responses were detected in most of the acute patients and were mostly CD4-dependent RdRp-specific responses. CD8-dependent VP1 and RdRp-specific responses were also detected in a small proportion of recently infected children. There was no significant association between the strength of the T-cell responses and disease severity observed during the acute EV71 infection phase. Interestingly, an RdRp-specific, but no VP1-specific, CD4-dependent T-cell response was detected in 30% of the adult controls, and no T-cell responses were detected in healthy children. In addition, 24 individual peptides containing potential T-cell epitope regions were identified. The data suggest that CD4-dependent RdRp-specific T-cell responses may play an important role in protective immunity, and the epitopes identified in this study should provide valuable information for future therapeutic and prophylactic vaccine design as well as basic research. [ABSTRACT FROM AUTHOR]

Inflammatory bowel disease ( IBD) is characterized by damage to the gut mucosa and systemic inflammation. We sought to evaluate the role of chronic inflammation on circulating T-cell activation in human subjects with Crohn's disease and ulcerative colitis. We studied 54 patients with IBD and 28 healthy controls. T-cell activation and cycling were assessed in whole blood samples by flow cytometry. Levels of lipopolysaccharide ( LPS) were measured in serum by Limulus amoebocyte lysate assay, and plasma levels of inflammatory markers and LPS-binding proteins were measured by ELISA. The proportions of circulating CD4+ and CD8+ T lymphocytes in cycle ( Ki67+) are increased in patients with IBD compared with these proportions in controls. CD8+ T cells from patients with IBD are also enriched for cells that expressed CD38 and HLA- DR, and proportions of these cells are related to plasma levels of interleukin-6 and C-reactive protein in these patients. Intracellular interleukin-2 and interferon-γ levels were elevated in resting and polyclonally activated CD4+ and CD8+ T cells in patients with IBD when compared with levels from healthy controls. Surprisingly, we did not find increased levels of LPS in the serum of patients with IBD. We did, however, find a signature of recent microbial translocation, as levels of LPS-binding protein are increased in the plasma of patients with IBD compared with plasma levels in healthy controls; LPS-binding protein levels are also directly related to proportions of CD38 HLA- DR-expressing CD4+ and CD8+ T cells. Local damage to the gastrointestinal tract in IBD may result in systemic inflammation and T-cell activation. [ABSTRACT FROM AUTHOR]

Among the milestones that occur during T-cell development in the thymus is the expression of T-cell receptor-β ( TCR-β) and the formation of the pre- TCR complex. Signals emanating from the pre- TCR trigger survival, proliferation and differentiation of T-cell precursors. Although the pre- TCR is essential for these cell outcomes, other receptors, such as Notch and CXCR4, also contribute. Whether interleukin-7 ( IL-7) participates in promoting the survival or proliferation of pre- TCR-expressing cells is controversial. We used in vitro and in vivo models of T-cell development to examine the function of IL-7 in TCR-β-expressing thymocytes. Culturing TCR-β-expressing CD4− CD8− double-negative thymocytes in an in vitro model of T-cell development revealed that IL-7 reduced the frequency of CD4+ CD8+ double-positive thymocytes at the time of harvest. The mechanism for this change in the percentage of double-positive cells was that IL-7 promoted the survival of thymocytes that had not yet differentiated. By preserving the double-negative population, IL-7 reduced the frequency of double-positive thymocytes. Interleukin-7 was not required for proliferation in the in vitro system. To follow this observation, we examined mice lacking CD127 ( IL-7Rα). In addition to the known effect of CD127 deficiency on T-cell development before TCR-β expression, CD127 deficiency also impaired the development of TCR-β-expressing double-negative thymocytes. Specifically, we found that Bcl-2 expression and cell cycle progression were reduced in TCR-β-expressing double-negative thymocytes in mice lacking CD127. We conclude that IL-7 continues to function after TCR-β is expressed by promoting the survival of TCR-β-expressing double-negative thymocytes. [ABSTRACT FROM AUTHOR]

Adult T-cell leukaemia-lymphoma (ATLL) is an aggressive malignancy of CD4+ CD25+ T lymphocytes, characterized by a severely compromised immunosystem, in which the human T-cell lymphotropic virus type 1 (HTLV-1) has been recognized as the aetiological agent. This study found that an IκB kinase β (IKKβ) inhibitor Bay11-7082 inactivated mammalian target of rapamycin ( mTOR), signal transducer and activator of transcription 3 and transcription factor nuclear factor-κB in HTLV-1-infected T cells; this was significantly enhanced in the presence of the mTOR inhibitor everolimus. In addition, Bay11-7082 decreased production of the immunosuppressive cytokine interleukin-10 (IL-10), which was further down-regulated when Bay11-7082 was combined with evelolimus in HTLV-1-infected T and ATLL cells isolated from patients. Interleukin-10 is known to inhibit maturation and the antigen-presenting function of dendritic cells (DCs). The culture media of HTLV-1-infected MT-1 cells, which contained a large amout of IL-10, hampered tumour necrosis factor-α-induced maturation of DCs isolated from healthy volunteers. Culture supernatant of MT-1 cells treated with a combination of Bay11-7082 and everolimus augmented maturation of DCs in association with a decrease in production of IL-10 and enhanced the allostimulatory function of DCs. Similarly, when DCs isolated from patients with ATLL were treated with the combination of Bay11-7082 and everolimus, they were fully matured and their capability to stimulate proliferation of lymphocytes was augmented. Taken together, the combination of Bay11-7082 and everolimus might exhibit immunostimulatory properties in HTLV-1-infected T and ATLL cells isolated from patients, and this combination may be potentially therapeutic to regain the compromised immunosystem in ATLL patients. [ABSTRACT FROM AUTHOR]

Summary Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is an important component of the inflammasome, functioning as an adaptor protein that facilitates the recruitment and activation of procaspases that in turn promote the maturation of interleukin-1β (IL-1β) and IL-18. Despite initial focus on the inflammatory properties of ASC there is emerging evidence that highlights the importance of ASC in facilitating adaptive immune responses. However, the cellular and molecular basis for the involvement of ASC in adaptive immunity remains largely unexplored. We have previously demonstrated that activated ASC-deficient T cells have dampened proliferative responses. We have therefore explored the underlying cellular mechanism(s) by which ASC regulates T-cell proliferation. We show that under activating conditions (anti-CD3/CD28 stimulation) in bulk T-cell cultures the presence of ASC−/− CD4+ T cells is sufficient to suppress the proliferative responses of neighbouring T cells. Furthermore, ASC−/− CD4+ T cells upon activation exhibit a suppressive cytokine profile, with elevated production of IL-10 and reduced secretion of T helper type 1 cytokines, interferon-γ and IL-2. This increase in IL-10 secretion within the activated ASC−/− CD4+ T-cell compartment was not associated with a proportional increase in conventional Foxp3+ regulatory T (Treg) cells. Interestingly, when equal numbers of fluorescence-activated cell sorted ASC+/+ and ASC−/− Treg cells (CD4+ CD44intermediate/high CD25+) were activated in vitro, the ASC−/− fraction produced significantly more IL-10 than their wild-type counterparts, suggesting that ASC−/− Treg cells have greater suppressive capacity. Collectively, these results imply that the ASC may influence the development and functioning of Treg cells. [ABSTRACT FROM AUTHOR]

It is widely accepted that antibodies and CD4 T cells play critical roles in the immune response during the blood stage of malaria, whereas the role of CD8 T cells remains controversial. Here, we show that both CD8 and CD4 T cells robustly responded to an acute self-limiting blood-stage infection with Plasmodium yoelii. Similar to antigen-specific T cells, both CD8 and CD4 T cells showed dynamic expression of the surface proteins interleukin (IL)-7R and programmed death-1 (PD-1). Additionally, activated CD8 T cells showed differences in the expression of Killer cell lectin-like receptor G1, L-selectin and B cell lymphoma-2 and produced granzyme B, indicating cytotoxic activity, and the initially high expression of T-box transcription factor TBX21 in malaria-activated CD4 T cells indicated an early T helper type 1 (Th1)-skewed immune response. Our data demonstrate that blood-stage malaria infection results in a striking T-cell response and that activated CD8 and CD4 T cells have phenotypic and functional characteristics that are consistent with conventional antigen-specific effector and memory T cells. Therefore, a better understanding of the CD8 and CD4 T-cell response induced by blood-stage infection may prove to be essential in the development of a vaccine that targets the erythrocytic stage of the malarial parasite. [ABSTRACT FROM AUTHOR]

The role of regulatory T cells (Treg) in maintaining tolerance to self has been intensively scrutinized, particularly since the discovery of Foxp3 as a Treg-specific transcription factor. The BDC2·5NOD transgenic mouse is an excellent model of immunoregulation because it has a very low incidence of diabetes despite a highly autoreactive T-cell repertoire. It has previously been shown that reactivity against islets decreases with age in BDC2·5NOD mice. Here we show that there is a markedly higher frequency of Foxp3+ Treg in the CD4+ subset of 16–20-week-old mice compared with 4- or 8-week-old mice. This phenomenon can be observed in the spleen, thymus, pancreatic draining lymph nodes and the pancreas itself. We show that this early age-related increase in the frequency of Foxp3+ cells does not occur in wild-type NOD, BALB/c or C57BL/6 mice. Further, we show that, in contrast to some reports on Treg in wild-type NOD mice, the suppressive function of BDC2·5NOD Treg from 16- to 20-week-old mice is intact and comparable to that from 4- to 8-week-old mice both in vitro and in vivo. Our data offer insights into the long-term protection of BDC2·5NOD mice from diabetes and an explanation for the age-related decrease in anti-islet responses seen in BDC2·5NOD mice. [ABSTRACT FROM AUTHOR]

The immune response of T lymphocytes to pathogens is initiated in draining secondary lymphoid organs, and activated cells then migrate to the site of infection. Thus, control of naïve and regulatory CD4+ T-cell migration is crucial; however, it is poorly understood in physiological and pathological conditions. We found that CD4+ subpopulations displayed characteristic regulator of G-protein signalling (RGS) gene expression profiles. Regulatory T cells express higher levels of RGS1, RGS9 and RGS16 than naïve cells. These genes are up-regulated upon cell activation and their level of expression correlates within vivocell migration. Using parabiosis, we showed that regulatory T lymphocytes migrate less than naïve T cells and that migrant naïve T cells express even lower RGS levels than their static counterparts. Our results show an inverse correlation between the capacity to migrate and the levels of RGS1, RGS9 and RGS16 for both naïve and regulatory T cells. Taken together, these results suggest a role for RGS molecules in chemokine-induced lymphocyte migration and demonstrate the peculiarity of regulatory T cells in terms of phenotype and migration ability, providing new insights into their function. [ABSTRACT FROM AUTHOR]

A mutant strain of rat, LEC, shows a novel arrest of T-cell maturation from CD4+8+ to CD4+8-, but not to CD4-8+ cells in the thymus. The responsible mutant locus is designated the thid, which was acted upon in a recessive manner of inheritance. We found that LEC rat thymocytes failed to respond to interleukin (IL)-1, IL-6 and IL-7 in the presence of the mitogenic lectins, Allo A or concanavalin A (Con A). The unresponsiveness appeared to be due to unresponsiveness to the lectin stimulation rather than because of cytokine stimulation. Normal rat CD4-8+/- (consisting of CD4-8+ and CD4-8- thymocytes), CD4+/-8- (consisting of CD4+8- and CD4-8- thymocytes), and CD4-8- thymocyte subsets normally responded to mitogenic stimulation, while CD4+8+ thymocytes did not. In contrast, all LEC rat CD4-8+/-, CD4+/-8-, CD4-8- and CD4-8+ thymocytes did not respond to the mitogenic stimulation, suggesting that the unresponsiveness of the CD4-8+/- thymocytes seems to be responsible for the unresponsiveness of whole thymocytes in LEC rats. LEC rat CD4-8+/- thymocytes normally expressed Con A receptor (R), lymphocyte function-associated antigen-1 (LFA-1), and CD45, which are thought to be important molecules for lectin stimulation. When backcross rats from (F344×LEC)F1×LEC were examined, the phenotype for the thid mutation correlated with the [3H]thymidine deoxyribose (TdR) incorporation level in response to Con A stimulation; thymocytes from backcross rats showing +/thid phenotype responded to Con A stimulation normally, whereas thymocytes from backcross rats showing thid/thid... [ABSTRACT FROM AUTHOR]

Tetanus toxoid (TT) and hepatitis B surface antigen (HBsAg) can suppress lectin-induced responses. The suppression induced by TT is dose-dependent and can also down-regulate the induction of a blastogenic response by anti-CD3 and anti-CD4 monoclonals. In addition, TT can dampen the blastogenic response induced by phytohaemagglutinin (PHA) and anti-CD3. The cellular mechanism involved in the turning off of the blastogenic response was investigated by transferring cells treated for 5 days with TT to freshly obtained syngeneic cells, and stimulation with PHA. The response of cultures that had received TT-treated cells was significantly lower than of those that had received cells treated with medium only. The removal of CD4+ cells at the induction phase of the suppression reversed the suppression, whereas the elimination of most CD8+ cells had no effect. We propose that CD4+ cells together with monocytes can dampen the specific and non-specific blastogenic responses. [ABSTRACT FROM AUTHOR]

Human and murine CD4+ T lymphocytes can be subdivided into distinct subsets [T-helper type 0 (TH0), Th1 or Th2], based on their lymphokine production profiles. Not much is known about the factors that determine these restricted lymphokine secretion profiles. Peptide specificity and human leucocyte antigen (HLA) restriction may be such factors. As it is well established that allergen-specific T lymphocytes from atopic individuals and non-atopic controls differ in their lymphokine secretion profile, we studied two allergen-specific T-lymphocyte clones (TLC) with identical peptide specificity and HLA restriction that were generated from the peripheral blood of an atopic donor and a non-atopic control donor. The two CD4+ TLC recognize the same epitope (20-33) of the house dust mite Dermatophagoides pteronyssinus major allergen Der p II. Both TLC recognize the epitope in an HLA-DQB1*0602-restricted manner. However, the lymphokine production profiles of these TLC show clear differences after allergen-specific or polyclonal activation. As expected, TLC JBD4 from the atopic donor produced high levels of interleukin-4 (IL-4) without detectable interferon-γ (IFN-γ), whereas TLC PBA1 from the non-atopic donor produced both IFN-γ, and IL-4 upon allergen-specific or polyclonal activation, inasmuch as both TLC recognized the same epitope of Der p II in association with the same HLA-DQ molecule, these data suggest that peptide specificity and HLA restriction of human allergen-specific TLC do not dictate their lymphokine secretion profile. [ABSTRACT FROM AUTHOR]

Previous studies have highlighted the importance of CD4′ T cells in regulation of IgA responses and have indicated a functional heterogeneity among these cells between inductive (Peyer's patch) and effector (lamina propria) sites in the intestine. To determine whether these functional differences could be accounted for by differences in cytokine profile of cells in each of these sites, the distribution of mRNA for interferon-γ (IFN-γ) and interleukin-6 (IL-6) was investigated by in situ hybridization techniques using 35S-labelled riboprobes. Whereas message for IL-6 is abundant in all regions of the lamina propria from the base of the mucosa to the tips of the villi, very little is expressed in Peyer's patches or in the epithelium. In contrast, message for IFN-γ is expressed predominantly by ceils localized only in the base of the lamina propria and, as with IL-6, very little message was detected in Peyer's patches although occasional strongly positive IFN-γ cells were observed in the epithelium. These results indicate that, at least in the absence of deliberate intestinal stimulation, functional expression of these cytokines is restricted to effector rather than induction sites in the intestine. This is consistent with our previous observations demonstrating a requirement for T-cell signals in promoting post-extravasation differentiation and proliferation of IgA-committed B cells in vivo and the implications of these findings to the role of the Thl and Th2 subsets of CD4+ cells in mucosal immune responses is discussed. [ABSTRACT FROM AUTHOR]

We examined the capacity of human Langerhans' cells (LC) to sensitize autologous T cells to the trinitrophenyl hapten (TNP) in vitro, Two-day cultured Langerhans' cells, but not freshly prepared Langerhans' cells, can induce in vitro primary proliferative reactions to the TNP hapten. Using a CE45RA+ naive T-cell subset, similar results were found, therefore making the possibility of a previous in vivo T-cell contact with the hapten unlikely. The primary in vitro response was strongly inhibited by monoclonal antibodies to major histocompatibility complex (MHC) class I and II, CD4 antigens and ICAM-1 and LFA-3 adhesion molecules. Furthermore, we found that fresh LC can prime T cells to TNP, as revealed by a significant secondary T-cell proliferation after restimulation of the recovered T lymphocytes by fresh hapten-modified autologous LC. Nevertheless, the ability of these fresh LC to stimulate in vitro secondary hapten-specific T-cell proliferation was very limited in comparison with that of 2-day incubated Langerhans' cells. After secondary stimulation with TNPcultured LC, sensitized T cells could be non-specifically expanded without losing hapten specificity. The TNP-specific T-cell lines were mostly of the CD4+ phenotype. The present findings extend previous studies in the mouse, showing that cultured LC are potent antigen-presenting cells (APC) in primary hapten-dependent proliferation assays. Furthermore, this in vitro priming assay, using cultured human Langerhans' cells as APC, might be useful to analyse the early steps of T-cell sensitization and subsequently to develop in vitro predictive tests allowing detection of sensitizing compounds. [ABSTRACT FROM AUTHOR]

Tumour necrosis factor (TNF) and interferon-gamma (IFN-γ) induce differentiation of human myeloid cell lines along the monocytic lineage. In this study we investigated the effects of TNF and IFN-γ on the expression of the CD4 protein and messenger RNA (mRNA) in the two myeloid cell lines, ML3 and HL-60. We observed that CD4 antigen expression on ML3 cells is almost undetectable and that TNF and IFN-γ induced CD4 antigen expression on these cells. HL-60 cells express surface CD4 antigen at high density and treatment with TNF and IFN-γ caused a decrease of CD4 expression. We also investigated the expression of CD4 mRNA in ML3 and HL-60 cells. ML3 constitutively express, albeit at low levels, CD4 mRNA. TNF induced CD4 mRNA in ML3 cells and IFN-γ synergistically potentiated the effect of TNF, thus indicating that the enhanced expression of the CD4 protein on ML3 cells is due, at least in part, to an enhanced accumulation of the CD4 mRNA. CD4 mRNA is constitutively expressed in HL-60 cells at high levels. TNF and IFN-γ, alone or in combination, did not cause any significant change of CD4 mRNA expression in HL-60 cells, thus indicating that decrease of surface CD4, which accompanies differentiation with these cytokines, is likely due to alterations of the CD4 protein synthesis and/or transport to the plasma membrane. These results provide evidence that myeloid cell lines are heterogeneous in expression of CD4, and that in ML3 cells, which constitutively express Iow levels of CD4 mRNA and undetectable amounts of surface CD4, the predominant effect of the two cytokines is to induce both CD4 mRNA and protein. [ABSTRACT FROM AUTHOR]

A polyanion binding site was identified recently on human CD4 which is distinct from the human immunodeficiency virus (HlV)-gp120 binding region but which incorporates the first two immunoglobulin (Ig)-like domains of the molecule. To determine if this site is conserved in other species, several polyanions that blocked monoclonal antibody (mAb) binding to human CD4 were examined for their ability to inhibit the binding of mAb to mouse, rat, pig, sheep and chicken CD4. It was found that aurintricarboxylic acid (ATA) was a particularly effective inhibitor, blocking mAb binding to human, mouse, pig, sheep and rat CD4 by > 90% and to chicken CD4 by 80–90%. The polyanions dextran sulphate (DxS), polyvinyl sulphate (PVS) and polyanethole sulphonate (PAS) were also effective inhibitors of anti-CD4 mAb binding in most species, although there were clear species differences in the effects obtained. The polyanions did not inhibit mAb binding to a variety of other cell-surface antigens in the different species, with the exception of sheep CD8, suggesting that the inhibitory effects observed were essentially CD4 specific. Collectively these data indicate that a polyanion binding site is conserved in mammalian and avian CD4. Comparison of the amino acid sequences of human, mouse and rat CD4 revealed that basic residues in human CD4 which could participate in a polyanion binding site are conserved in mouse and rat CD4. It is proposed that this conserved polyanion binding site of CD4 interacts with a sulphated glycosaminoglycan chain which is associated with class II major histocompatibility complex (MHC) molecules containing recently processed antigen. [ABSTRACT FROM AUTHOR]

Compared to their normal, T-cell competent counterparts, BALB/c mice that have been thymectomized, lethally irradiated, and reconstituted with bone marrow cells (TXB) were found to be resistant to Leishmania major. Even though TXB mice possess less than 30% of the normal number oft cells in their lymphoid organs, they generated a protective immune response that prevented the progressive multiplication of the parasite in the primary cutaneous lesion and its dissemination to distant visceral sites. Studies of TXB mice depleted of residual CD4+ or CD8+ T cells by systemic monoclonal antibody (mAb) treatment showed that this protective immunity depends on a residual, radioresistant CD8+ T-cell population, and that it develops in the virtual absence of CD4+ T cells. This immune response can be negated by an infusion of CD4+ T cells from normal susceptible donors, provided that the donor cells are infused before the recipients' response is generated. It is therefore apparent that TXB BALB/c mice are more resistant than T-cell competent BALB/c mice because the former mice lack a threshold number of CEM+ suppressor T cells necessary to down-regulate the induction and expansion of CD8+ protective T cells. [ABSTRACT FROM AUTHOR]

Tissue-specific and lymphocyte subset-specific lymphocyte recirculation patterns have been analysed simultaneously. Lymphocytes obtained from one lymph compartment were directly labelled with fluorochrome in vitro and returned to the blood of the same animal. Over the next 48-72 h, the recirculation of these cells into both the same lymph compartment and at least one different lymph compartment was monitored. The cells in all of these lymph collections, as well as an aliquot of the cells used for direct fluorescent labelling, were then phenotyped with monoclonal antibodies (mAb) which define the mutually exclusive small CD4+ and CD8+ T-lymphocyte subsets in sheep. All cell samples were analysed by flow cytometry and CD4/CD8 ratios were determined for the recireulated, fluorochrome-labelled population in each lymph collection. The mean CD4/CD8 ratio calculated for each lymph compartment was then compared with the CD4/CD8 ratio of the transfused, starting population. In one experiment employing efferent prescapular lymph cells, three experiments employing efferent intestinal lymph cells, and two experiments employing afferent intestinal lymph cells, tissue-specific recirculation was observed. In all of these experiments, the pattern of recirculation of small CD4+ and CD8+ T lymphocytes was non-random. Moreover, in each experiment, this non-randomness was completely unrelated to tissue-specific phenomena, since the mean CD4/CD8 ratio of the recirculated population was higher than the CD4/CD8 ratio of the transfused, starting population regardless of the lymph compartment examined. These data are therefore consistent with the hypothesis that tissue-specific and lymphocyte subset-specific lymphocyte-endothelial cell recognition mechanisms independently direct the recirculation of small lymphocytes from blood to lymph. [ABSTRACT FROM AUTHOR]

In the mouse, using three-colour flow cytometry, the presence of CD45RA+ cells is demonstrated amongst all of the thymocyte subsets defined by expression of CD4 and CD8, i.e. amongst the double negatives, immature CD8 single positives, double-positive blasts and CD4 and CD8 single positives. This evidence is compatible with the existence of a continuous lineage oft cells expressing CD45RA which would develop from double-negative to mature single-positive T cells. [ABSTRACT FROM AUTHOR]