Monocyte tissue factor induction by activation of beta 2-glycoprotein-I-specific T lymphocytes is associated with thrombosis and fetal loss in patients with antiphospholipid antibodies

Antiphospholipid (aPL) syndrome (APS) is characterized by thromboembolic events, thrombocytopenia, or recurrent miscarriage associated with aPL Abs with specificity for beta2-glycoprotein-I (beta2GPI). We recently reported that at least 44% of patients with the APS possess circulating type 1 (Th1) CD4+ T cells that proliferate and secrete IFN-gamma when stimulated with beta2GPI in vitro. In this study, we show that stimulation of PBMCs from 20 APS patients with beta2GPI induced substantial monocyte tissue factor (TF) (80 +/- 11 TF stimulation index (TF-SI)), whereas no induction was observed using PBMCs from 13 patients with aPL Abs without APS (6 +/- 1 TF-SI) or 7 normal and 7 autoimmune controls (5 +/- 1 and 3 +/- 1 TF-SI, respectively) (p < 0.0001). TF induction on monocytes by beta2GPI was dose dependent and required CD4+ T lymphocytes and class II MHC molecules. Because monocyte TF induction by beta2GPI was observed in all patients with APS, but not in any patient with aPL Abs without APS, this response is a potentially useful predictor for APS in patients with aPL Abs, as well as providing mechanistic insight into thrombosis and fetal loss in these patients.     

Allergen rush immunotherapy increases interleukin (IL)-12 production and IL-12 receptor beta2 chain expression in patients with allergic asthma

Interleukin (IL)-12 production and IL-12 receptor (IL-12R) beta2 chain expression were investigated in patients with allergic asthma successfully treated with rush immunotherapy (RIT) and control patients with mild allergic asthma. Peripheral blood mononuclear cells (PBMCs) were stimulated with Dermatophagoides farinae (Der f), and production of cytokines was measured. Furthermore, the effects of cytokines on IL-12R beta2 chain expression on CD4(+) T cells were investigated. Production by PBMCs of IL-12 and IFN-gamma was significantly higher and production of IL-4 was significantly lower after stimulation with Der f allergen in RIT-treated patients than in control patients. Significant increases in the expression of IL-12R beta2 chain before and after stimulation of CD4(+) T cells with IL-12 or IFN-gamma were observed in RIT-treated patients compared with that in control patients. Allergen RIT increases IL-12 production and IL-12R beta2 chain expression and thus may convert cytokine production from Th2 to Th1 or Th0 type in allergic asthma.     

Effects of Astragalus polysaccharide on immune responses of porcine PBMC stimulated with PRRSV or CSFV

Background

Astragalus polysaccharide (APS) has been used as an immunomodulator that can enhance immune responses, whereas the immunomodulatory effects of APS on porcine peripheral blood mononuclear cells (PBMCs) exposed to porcine reproductive and respiratory syndrome virus (PRRSV) and classical swine fever virus (CSFV) have not been investigated.

Methodology/Principal Findings

Porcine PBMCs were cultured in complete RPMI media in the presence of the R98-strain of PRRSV (5×10⁴ TCID₅₀/ml) or C-strain of CSFV (10³ TCID₅₀/ml) with or without APS. The expression of mRNA for CD28, cytotoxic T-lymphocyte antigen 4 (CTLA-4), transforming growth factor-β (TGF-β), interleukin 2 (IL-2) and IL-10 was assayed by TaqMan real-time RT-PCR. The expression of mRNA for CD28 and CTLA-4 increased at 24 h after stimulation of PBMCs with CSFV and the increased production of CTLA-4 was confirmed by western blot analysis, whereas the increases were inhibited by the addition of APS. In addition, APS alone upregulated IL-2 and TGF-β mRNA expression in PBMCs and the addition of APS had the capacity to prevent a further increase in IL-2 mRNA expression in PBMCs during CSFV or PRRSV infection, but had no effect on TGF-β mRNA expression. The production of tumor necrosis factor-alpha (TNF-α) increased at 12 h after stimulation with PRRSV or CSFV, but not with PRRSV plus APS or CSFV plus APS, whereas the addition of APS to PBMCs infected with PRRSV or CSFV promoted IL-10 mRNA expression.

Conclusions

We suggested that APS had immunomodulatory effects on cells exposed to PRRSV or CSFV. It might be that APS via different mechanisms affects the activities of immune cells during either PRRSV or CSFV infection. This possibility warrants further studies to evaluate whether APS would be an effective adjuvant in vaccines against PRRSV or CSFV.     

Deficiency of the CD3-TCR signal pathway in three patients with idiopathic CD4+ lymphocytopenia

Idiopathic CD4+ lymphocytopenia (ICL) is a rare syndrome affecting adults and defined by a stable loss of CD4+ T cells in the absence of any known cause of immune deficiency. Defective T-cell proliferations to mitogens and antigens have been described in some of such patients displaying clinical signs of immune deficiency such as opportunistic infections. We investigated here the hypothesis that T-cell depletion and dysfunction could be due to biochemical defects of the CD3-TCR pathway in CD4+ and/or CD8+ subsets from three patients with severe stable ICL (below 150 CD4+ T cells/microliter) and opportunistic infections. Patient 1 had a general T lymphocytopenia, whereas patients 2 and 3 displayed a selective loss of CD4+ T cells. We observed in all patients a major reduction of the proliferative response to CD3-TCR stimulation that affected only the depleted T-cell subpopulation. Moreover, in two cases, impaired early biochemical events of the CD3-TCR pathway were detected. In patient 1 and 3, we found a defect (of distinct intensity) of CD3-induced protein tyrosine phosphorylation in CD4+ cells compared to control cells, whereas this process was normally induced in CD4+ T cells from patient 2. Taken together, this study reveals that the heterogeneity of the ICL syndrome was situated at the cellular level, and involved in two cases abnormalities of transducing molecules of the CD3-TCR pathway.     

Neural progenitor cells from human induced pluripotent stem cells generated less autogenous immune response

The breakthrough development of induced pluripotent stem cells(iPSCs)raises the prospect of patient-specific treatment for many diseases through the replacement of affected cells.However,whether iPSC-derived functional cell lineages generate a deleterious immune response upon auto-transplantation remains unclear.In this study,we differentiated five human iPSC lines from skin fibroblasts and urine cells into neural progenitor cells(NPCs)and analyzed their immunogenicity.Through co-culture with autogenous peripheral blood mononuclear cells(PBMCs),we showed that both somatic cells and iPSC-derived NPCs do not stimulate significant autogenous PBMC proliferation.However,a significant immune reaction was detected when these cells were co-cultured with allogenous PBMCs.Furthermore,no significant expression of perforin or granzyme B was detected following stimulation of autogenous immune effector cells(CD3+CD8 T cells,CD3+CD8+T cells or CD3 CD56+NK cells)by NPCs in both PBMC and T cell co-culture systems.These results suggest that human iPSC-derived NPCs may not initiate an immune response in autogenous transplants,and thus set a base for further preclinical evaluation of human iPSCs.     

Human memory T cell responses to SARS-CoV E protein

E protein is a membrane component of severe acute respiratory syndrome coronavirus (SARS-CoV). Disruption of E protein may reduce viral infectivity. Thus, the SARS-CoV E protein is considered a potential target for the development of antiviral drugs. However, the cellular immune responses to E protein remain unclear in humans. In this study, we found that peripheral blood mononuclear cells (PBMCs) from fully recovered SARS individuals rapidly produced IFN-gamma and IL-2 following stimulation with a pool of 9 peptides overlapping the entire E protein sequence. Analysis of the immune responses by flow cytometry showed that both CD4+ and CD8+T cells were involved in the SARS-CoV E-specific immune responses after stimulation with SARS-CoV E peptides. Moreover, the majority of IFN-gamma+CD4+T cells were central memory cells expressing CD45RO+CCR7+CD62L-; whereas IFN-gamma+CD8+ memory T cells were mostly effector memory cells expressing CD45RO-CCR7-CD62L-. The results of T-cell responses to 9 individual peptides indicated that the E protein contained at least two major T cell epitopes (E2 amino acid [aa] 9-26 and E5-6: aa 33-57) which were important in eliciting cellular immune response to SARS-CoV E protein in humans.     

Impaired effector function of hepatitis C virus-specific CD8+ T cells in chronic hepatitis C virus infection

The cellular immune response contributes to clearance of hepatitis C virus (HCV) and persists for decades after recovery from infection. The immunological basis for the inefficiency of the cellular immune response in chronically infected persons is not known. Here, we used four HLA-A2 tetramers, specific for two HCV core and two HCV NS3 epitopes, to investigate at the single-cell level effector function and phenotype of HCV-specific CD8+ T cells in 20 chronically infected and 12 long-term recovered patients. Overall, HCV-specific, tetramer+ T cells were more frequently found in PBMCs of chronically infected patients than in those of recovered patients. However, when compared with HCV-tetramer+ T cells of recovered patients, they displayed an impaired proliferative capacity. As a result of the impaired proliferative capacity, HCV-specific T cell lines derived from chronically infected patients displayed less peptide-specific cytotoxicity than those from recovered patients. In addition, proliferation and ex vivo IFN-gamma production of HCV-tetramer+ cells, but not influenza-virus-specific T cells, were defective in chronically infected patients and could not be restored by in vitro stimulation with peptide and IL-2. At least three distinct phenotypes of HCV-specific CD8+ T cells were identified and associated with certain functional characteristics. In addition, impairment of proliferative, cytokine, and cytotoxic effector functions of tetramer+ T cells in viremic patients was associated with weak ex vivo HCV-specific CD4+ T cell responses. Thus, the defective functions of HCV-specific CD8+ T cells might contribute to viral persistence in chronically infected patients, and knowledge on their reversibility may facilitate the development of immunotherapeutic vaccines.     

Activation of extracellular signaling regulated kinase in natural killer cells and monocytes following IL-2 stimulation in vitro and in patients undergoing IL-2 immunotherapy: analysis via dual parameter flow-cytometric assay

Interleukin-2 (IL-2) activates extracellular signal-regulated protein kinase (ERK) within immune cells. To examine the profile of phosphorylated ERK (p-ERK) in IL-2 stimulated immune cells of normal donors and patients receiving IL-2 therapy, we developed a dual parameter flow-cytometric assay. An analysis of PBMCs stimulated with IL-2 indicated that IL-2 exposure induced p-ERK in CD56bright NK cells and CD14+ monocytes, but not in CD3+ T cells or CD21+ B cells. CD3+ T cells that were induced to express functional high-affinity IL-2R did not exhibit enhanced p-ERK following IL-2 treatment. Measurement of p-ERK within PBMCs from cancer patients 1 h following their first dose of IL-2 revealed a complete absence of circulating NK cells, consistent with earlier observations. However, the total number of circulating CD14+ monocytes increased in these samples and 97% of these cells exhibited ERK activation. p-ERK was not observed in T cells post-IL-2 therapy. Analysis of PBMCs obtained 3 weeks post-IL-2 therapy revealed high-p-ERK levels in CD56bright NK cells in a subset of patients, while levels of p-ERK returned to baseline in monocytes. These studies reveal an effective method to detect ERK activation in immune cells and demonstrate that IL-2 activates ERK in a subset of NK cells and monocytes but not T cells.     

A soluble form of lymphocyte activation gene-3 (IMP321) induces activation of a large range of human effector cytotoxic cells

The principal antitumor immune response is mediated through the activation of type 1 cytotoxic (Tc1) CD8 T cells, NK cells, and monocytes/macrophages. In this study, we investigated the potency of a clinical-grade soluble form of lymphocyte activation gene-3 protein (IMP321), a physiological high-affinity MHC class II binder, at inducing in PBMCs an appropriate cytotoxic-type response in short-term ex vivo assays. We found that IMP321 binds to a minority (<10%) of MHC class II + cells in PBMCs, including all myeloid dendritic cells, and a small fraction of monocytes. Four hours after addition of IMP321 to PBMCs, these myeloid cells produce TNF-alpha and CCL4 as determined by intracellular staining. At 18 h, 1% of CD8+ T cells and 3.7% NK cells produce Tc1 cytokines such as IFN-gamma and/or TNF-alpha (mean values from 60 blood donors). Similar induction was observed in metastatic cancer patient PBMCs, but the values were lower for the NK cell subset. Early APC activation by IMP321 is needed for this Tc1-type activation because pure sorted CD8+ T cells could not be activated by IMP321. Only Ag-experienced, fully differentiated granzyme+ CD8 T cells (effector and effector memory but not naive or central memory T cells) are induced by IMP321 to full Tc1 activation. In contrast to IMP321, TLR1-9 agonists induce IL-10 and are therefore unable to induce this Tc1 IFN-gamma+ response. Thus, IMP321 has many properties that confirm its potential to be a new class of immunopotentiator in cancer patients.     

Generation and growth of CD28nullCD8+ memory T cells mediated by IL-15 and its induced cytokines

Accumulation of CD28(null)CD8+ T cells and the defects of these cells in response to antigenic stimulation are the hallmarks of age-associated decline of T cell function. However, the mechanism of these age-associated changes is not fully understood. In this study, we report an analysis of the growth of human CD28(null) and CD28+CD8+ memory T cells in response to homeostatic cytokine IL-15 in vitro. We showed that 1) there was no proliferative defect of CD28(null)CD8+ memory T cells in response to IL-15 compared with their CD28+ counterparts; 2) stable loss of CD28 expression occurred in those actively dividing CD28+CD8+ memory T cells responding to IL-15; 3) the loss of CD28 was in part mediated by TNF-alpha that was induced by IL-15; and 4) CCL4 (MIP-1beta), also induced by IL-15, had a significant inhibitory effect on the growth of CD28(null) cells, which in turn down-regulated their expression of CCL4 receptor CCR5. Together, these findings demonstrate that CD28(null)CD8+ memory T cells proliferate normally in response to IL-15 and that IL-15 and its induced cytokines regulate the generation and growth of CD28(null)CD8+ T cells, suggesting a possible role of IL-15 in the increase in CD28(null)CD8+ T cells that occurs with aging.     

Regulation of T cell responses in the developing human fetus

Although human T cells enter the peripheral lymphoid tissues early during fetal development, the adaptive immune system in the fetus has largely been regarded as functionally immature and unresponsive to stimulation. In this study, we show that depletion of fetal CD4+CD25(high) T regulatory (T(Reg)) cells, which are present at high frequency in fetal lymphoid tissues, results in vigorous T cell proliferation and cytokine production in vitro, even in the absence of exogenous stimulation. Analysis of CD4+ and CD8(+) T cell populations revealed a large subset of cells that expressed the early activation Ag, CD69. We show that this population represents a subset of highly reactive fetal T cells actively suppressed by fetal CD4+CD25(high) T(Reg) cells during development. These findings indicate that fetal T cells are, in the absence of CD4+CD25(high) T(Reg) cells, highly responsive to stimulation and provide evidence for an important role for CD4+CD25(high) T(Reg) cells in controlling T cell responses in utero.     

Co-expression of IL-12 receptors along with CXCR3 and CD25 on activated peripheral blood T lymphocytes

IL-12 receptors (IL-12R) play a critical role in maintaining IL-12 regulation of T helper-1 (Th1) type immune responses. We studied the expression of two IL-12R, beta1 and beta2 on peripheral blood mononuclear cells (PBMCs) from normal donors, stimulated with polyclonal activators in the presence or absence of exogenous rhIL-12. Unstimulated peripheral blood T lymphocytes (PBTs) expressed moderate levels of IL-12Rbeta1 and very low to undetectable levels of IL-12Rbeta2. Superantigens and anti-CD3+anti-CD28 induced higher expression of both IL-12R on PBTs than PHA-P stimulation. Exogenous rhIL-12 further enhanced the PHA-P or anti-CD3+anti-CD28 induced IL-12Rbeta2 expression. Only a fraction of mitogen activated IL-12Rbeta1+ or beta2+ T lymphocytes co-expressed CD25 (with further enhancement by exogenous rhIL-12), while a higher percentage of these cells were CXCR3+. The majority of superantigen or anti-CD3+anti-CD28-induced IL-12R+ PBTs were positive for both CD25 and CXCR3 markers. Our results indicated differential induction of IL-12R expression that correlated with up regulation of CD25 and CXCR3 expression on activated PBTs and provide a useful insight for monitoring these markers during treatment of Th1 type inflammatory diseases.     

Immunomodulation mediated through Leishmania donovani protein disulfide isomerase by eliciting CD8+ T-cell in cured visceral leishmaniasis subjects and identification of its possible HLA class-1 restricted T-cell epitopes

Protein disulphide isomerase (PDI) is one of the key enzymes essential for the survival of Leishmania donovani in the host. Our study suggested that PDI is associated with the generation of Th1-type of cellular responses in treated Visceral leishmaniasis (VL) subjects. The stimulation of Peripheral blood mononuclear cells (PBMCs) with recombinant Protein Disulphide Isomerase upregulated the reactive oxygen species generation, Nitric oxide release, IL12 and IFN-γ production indicating its pivotal role in protective immune response. Further, a pre-stimulation of PBMCs with Protein disulphide isomerase induced a strong IFN-γ response through CD8+ T cells in treated VL subjects. These findings also supported through the evidence that this antigen was processed and presented by major histocompatibility complex class I (MHC-1) dependent pathway and had an immunoprophylactic potential which can induce CD8+ T cell protective immune response in MHC class I dependent manner against VL. To find out the possible epitopes that might be responsible for CD8+ T cell specific IFN-γ response, computational approach was adopted. Six novel promiscuous epitopes were predicted to be highly immunogenic and can be presented by 32 different HLA allele to CD8+ T cells. Further investigation will explore more about their immunological relevance and usefulness as vaccine candidates.     

Impaired clonal expansion in athymic nude CD8+CD4- T cells

A comparative study of the phenotype and immune functions of highly purified CD8+CD4- T cells obtained from the spleen and thymus of normal mice and from the spleen of athymic nude mice was conducted. Of seven individual normal and nude mice examined, the range of V beta 8+ cells among CD8+ T cells was a heterogeneous 4.3 to 30.5% for athymic nude mice and a much more uniform spread from 14.7 to 18.5% for normal mice. In six of the seven nude mice examined, the fraction of V beta 8+ cells was below the lower limit of the V beta 8 distribution in normal mice. However, one of the seven nude mice contained nearly twice the percentage of normal V beta 8+ cells. A reduction in the density of V beta 8 as well as CD3 Ag expression was also observed in athymic CD8+CD4- cells although an Ly-6-linked Ag, B4B2 displayed a highly increased expression. Considering the battery of Ag analyzed in entirety, athymic CD8+CD4- T cells were clearly distinct from their "counterpart" CD8+CD4- T cells isolated from either thymus or spleen of normal (euthymic) mice. Anti-CD3-mediated triggering of the TCR:CD3 complex caused extensive clonal proliferation in cultures to which single responding CD8+ T cells had been deposited. Under identical conditions, however, anti-CD3 caused little, if any clonal expansion in CD8+ cells from athymic nude mice. Highly purified athymic CD8+CD4- cells produced readily detectable IL-2R expression and IL-2 synthesis and secretion upon stimulation by anti-CD3 and by Con A. Production of IL-2 by purified athymic CD8+CD4- cells was due to CD8+CD4- cells and not due to a minor population of contaminating CD8- cells as anti-CD8 + C treatment completely abrogated the ability of athymic CD8+CD4- cells to produce IL-2. Despite IL-2 production and IL-2R expression by athymic nude CD8+CD4- T cells in response to anti-CD3 and to Con A, an impaired proliferative response followed.     

Developmentally regulated expression of the beta 4 integrin on immature mouse thymocytes.

Integrins are a superfamily of alpha beta heterodimers, most of which serve as cell surface receptors for extracellular matrix proteins. In this report, we demonstrate that the recently described alpha 6 beta 4 integrin, previously thought to be limited to epithelial cells and Schwann cells, is expressed on immature mouse thymocytes. The presence of alpha 6 beta 4 is controlled by regulation of beta 4 expression, because alpha 6 was expressed by virtually all cells examined, paired with the beta 1 integrin chain to form VLA-6. During fetal ontogeny, beta 4 was highly expressed by 35% of day-13 thymocytes, 75% of day-14 to -15 thymocytes, then rapidly declined to low levels by birth. In neonates and adults, beta 4 expression was highest on CD4- CD8- CD3- and TCR(+)-gamma delta subsets. Correlation of IL-2R, CD44 and beta 4 on CD4- CD8- thymocytes revealed maximal levels on the intermediate CD44- IL-2R+ subset. Most CD4- CD8+ TCR- thymocytes and a significant fraction of CD4+ CD8+ thymocytes were beta 4lo, whereas the most mature J11d- single positive thymocytes were beta-4. Overall, down-regulation of beta 4 was associated with up-regulation of CD4, CD8, and CD3 in the thymus. alpha 6 beta 4 was undetectable on fetal liver or bone marrow cells, lymphocytes from lymph node, spleen, or blood, and mitogen-activated splenic T cells cultured up to 10 wk with IL-2. The data suggest that alpha 6 beta 4 is up-regulated after pro-T cells enter the thymus and may have a thymus-specific function for T cells. The developmentally regulated pattern of expression and the prominence of alpha 6 beta 4 on day-13 to -16 fetal and adult CD4- CD8- CD3- thymocytes further suggest this unusual integrin may play a role in early T cell development, including stages before acquisition of the TCR.     

Analysis of expression of CD2, CD3, and T cell antigen receptor molecules during early human fetal thymic development

To define early stages of T cell maturation during human fetal thymic development, we have used mAb reactive with CD2, CD3, and TCR molecules in indirect immunofluorescence assays on a series of early human fetal thymic specimens. Using a technique of quantitating the relative proportions of fluorescent-positive cells present in tissue sections, we found at 8.5 wk of gestational age after arrival of CD7+ T cell precursors into the thymic rudiment, 60% of thymic CD7+ cells were CD2+, 4% were CD3+ and none was TCR-delta+ or TCR beta+. Moreover, cells reactive with anti-CD2 antibodies against T11(2) and T11(3) epitopes of CD2 as well as thymic stromal cells expressing the CD2 ligand, lymphocyte function associated Ag-3, were also present at 8.5 wk. From 9.5 wk to birth TCR beta+ cells increased to include greater than 90% of all CD7+ cells while TCR-delta+ cells fell from a peak of 11% of CD7+ cells at 9.5 wk to 1% of CD7+ cells at birth. These data suggest that epitopes of CD2 molecules are expressed early on during fetal thymic development. Moreover, these data suggest that CD7+, CD2+, cytoplasmic CD3+ T cell precursors in man give rise to both TCR-delta+ T cells as well as to T cells expressing TCR-alpha beta.     

Human CD4- CD8- alpha beta+ T cells express a functional T cell receptor and can be activated by superantigens.

The CD4 and CD8 molecules play an important role in the stimulation of T cells and in the process of thymic education. Most mature T cells express the alpha beta TCR and either CD4 or CD8; however, there is a small population of alpha beta+ TCR T cells that lack both CD4 and CD8. Little is known of the biology of the CD4- CD8- (double-negative) alpha beta+ TCR T cells or the nature of the Ag to which they may respond. These cells not only represent a novel population of T cells but also provide useful biologic tools to study the roles that CD4 and CD8 play in T cell activation. In this study we have addressed two questions. Firstly, whether CD4- CD8- alpha beta+ TCR T cells have functionally active TCR and, secondly, whether CD4 or CD8 is required for the activation of T cells by bacterial enterotoxins. Six double-negative alpha beta+ TCR T cell clones, propagated from two healthy donors, were challenged with a panel of nine bacterial enterotoxins. The V alpha and V beta usage of their TCR was determined by polymerase chain reaction. All of the CD4-CD8- clones proliferated in response to at least one of the enterotoxins, in a V beta-specific manner. The proliferative response of the CD4-CD8- alpha beta+ TCR T cell clones was similar in magnitude to that exhibited by CD4+ T cell clones of known V beta expression. These data clearly show that the CD4 and CD8 molecules are not required for the activation of untransformed human T cells by bacterial enterotoxins. Furthermore, these results indicate that CD4-CD8- alpha beta+ TCR T cells, normally present in all individuals, are not functionally silent, because they can be stimulated via their TCR. Their physiologic role, like that of gamma delta T cells, remains to be elucidated.     

CD1d-independent developmental acquisition of prompt IL-4 gene inducibility in thymus CD161(NK1)-CD44lowCD4+CD8- T cells is associated with complementarity determining region 3-diverse and biased Vbeta2/Vbeta7/Vbeta8/Valpha3.2 T cell receptor usage

Among Ag-inexperienced naive T cells, the CD1d-restricted NKT cell that uses invariant TCR-alpha-chain is the most widely studied cell capable of prompt IL-4 inducibility. We show in this study that thymus CD161-CD44lowCD4+CD8- T cells promptly produce IL-4 upon TCR stimulation, a response that displays biased Vbeta(2/7/8) and Valpha3.2 TCR usage. The association of Vbeta family bias and IL-4 inducibility in thymus CD161-CD44lowCD4+CD8- T cells is found for B6, B10, BALB/c, CBA, B10.A(4R), and ICR mouse strains. Despite reduced IL-4 inducibility, there is a similarly biased Vbeta(2/7/8) TCR usage by IL-4 inducibility+ spleen CD161-CD44lowCD4+CD8- T cells. Removal of alpha-galacotosylceramide/CD1d-binding cells from CD161-CD44lowCD4+CD8- thymocytes does not significantly affect their IL-4 inducibility. The development of thymus CD161-CD44lowCD4+CD8- T cells endowed with IL-4 inducibility and their associated use of Vbeta(2/7/8) are beta2-microglobulin-, CD1d-, and p59fyn-independent. Thymus CD161-CD44lowCD4+CD8- T cells produce low and no IFN-gamma inducibility in response to TCR stimulation and to IL-12 + IL-18, respectively, and they express diverse complementarity determining region 3 sequences for both TCR-alpha- and -beta-chains. Taken together, these results demonstrate the existence of a NKT cell distinct, TCR-repertoire diverse naive CD4+ T cell subset capable of prompt IL-4 inducibility. This subset has the potential to participate in immune response to a relatively large number of Ags. The more prevalent nature of this unique T cell subset in the thymus than the periphery implies roles it might play in intrathymic T cell development and may provide a framework upon which mechanisms of developmentally regulated IL-4 gene inducibility can be studied.