Takuma Kato

Polarization of Naive CD4+ T Cells Toward the Th1 Subset by CTLA-4 Costimulation

In this study, we examined in vitro the role of CTLA-4 costimulation in the polarization of naive CD4+ T cells toward the Th1 subset. When CTLA-4 costimulation was blocked by the inclusion of anti-CTLA-4 Fab in cultures during priming of naive CD4+ T cells with anti-CD3 in the presence of splenic adherent cells, they were polarized toward the Th2 subset. Conversely, the engagement of CTLA-4 with immobilized anti-CTLA-4 or with CD80-P815 cells polarized naive CD4+ T cells costimulated with anti-CD3 and anti-CD28 toward the Th1 subset. The CTLA-4 costimulation during priming augmented TGF-β1 mRNA accumulation in naive CD4+ T cells, and the inclusion of anti-TGF-β in cultures for priming suppressed the effect of CTLA-4 costimulation on the Th1 polarization. The addition of low doses of TGF-β1 in cultures for priming of naive CD4+ T cells enhanced the production of Th1 cytokines upon secondary stimulation, although Th2 cytokine production was not affected by the doses of TGF-β1. The CTLA-4 costimulation was also shown to suppress IL-4 production of naive CD4+ T cells upon priming. These results indicate that the costimulation against CTLA-4 drives polarization of naive CD4+ T cells toward the Th1 subset independent of IL-12 through, at least in part, the enhancement of TGF-β1 production, and it also hampers Th2 subset differentiation by affecting IL-4 production of naive CD4+ T cells.

Expression and co-stimulatory function of B7-2 on murine CD4+ T cells.

Co‐stimulatory signals mediated by the interaction of B7‐1/B7‐2 with CD28 are important for the activation of CD4+ T cells stimulated with antigen on antigen‐presenting cells. There are controversies about the expression and function of B7‐1/B7‐2 on CD4+ T cells. The aim of this study was to analyze the expression of B7‐1/B7‐2 on naive and memory CD4+ T cells and the co‐stimulatory function in the activation of naive CD4+ T cells stimulated by TCR ligation. Present results indicate that memory CD4+ T cells express B7‐2 molecules on their surface, whereas naive CD4+ T cells do not. Neither memory nor naive CD4+ T cells expressed B7‐1 molecule on their surface, although B7‐1 mRNA was faintly expressed in memory T cells. B7‐2 molecules expressed on memory T cells co‐stimulated CD4+ naive T cells stimulated with plate‐coated anti‐CD3 to produce IL‐2. Naive CD4+ T cells were shown to express B7‐2 after co‐stimulation with B7‐2 and TCR ligation, because the naive T cells stimulated with anti‐CD3 and B7‐2CHO expressed B7‐2 on their surface, although it remained to be studied whether the co‐stimulation with B7‐2 directly induced B7‐2 expression on naive T cells. Our present results indicate that memory CD4+ T cells play some role in the activation of naive CD4+ T cells through the co‐stimulation with B7‐2 molecules.

Impairment in the Expression and Activity of Fyn During Differentiation of Naive CD4+ T Cells into the Th2 Subset

We previously showed that the amounts of Fyn protein in Th2 clones were approximately one-third to one-fifth of those in Th1 clones. In this study we examined the role of Fyn in the polarization of naive CD4+ T cells toward the Th2 subset using fyn−/− mice. The fyn−/− naive CD4+ T cells efficiently produced Th2 cytokines and polarized toward the Th2 subset even in the absence of IL-4 and IL-13. The expression of Fyn in wild-type CD4+ T cells decreased at a transcription level concomitant with polarization toward the Th2 subset. These results suggest that Fyn plays a role in the down-regulation of the differentiation of naive CD4+ T cells into the Th2 subset.

Positive and negative regulation of IL-12 receptor expression of naive CD4 + T cells by CD28/CD152 co-stimulation

IL‐12 is a critical cytokine for polarizing naive CD4+ T cells toward Th1 subset. Therefore, it is important to elucidate the mechanism of IL‐12R expression of naive CD4+ T cells. In this report, we present evidence to show that expression of both IL‐12Rβ1 and β2 mRNA is regulated by signals mediated through CD28 and CD152. Naive CD4+ T cells stimulated with anti‐CD3 alone neither expressed IL‐12Rβ2 mRNA nor bound detectable level of rIL‐12, although they expressed a very low level of IL‐12Rβ1 mRNA when stimulated with a high dose of anti‐CD3. Expression of IL‐12Rβ1 and β2 mRNA was induced by the co‐ligation of CD3 and CD28, and it was down‐regulated by the ligation of CD152. CD28 ligation induced not only IL‐12Rβ1 and β2 mRNA expression, but also enhanced IFN‐γR to mediate up‐regulation of IL‐12R by IFN‐γ.

Induction of IL-2 receptor expression and proliferation of T cell clones by a novel cytokine(s)

We found a unique T cell IL-2 receptor (IL-2R)3-inducing activity in the supernatant (SN) of the TH1 clone stimulated with antigen on spleen cells as antigen-presenting cells (APC). We have tentatively named this activity the IL-2R-inducing factor (IL-2RIF) and have characterized the activity. The SN induced IL-2R and proliferation of TH1 clones stimulated with B cell APC, which could not induce IL-2R in the absence of the SN. Other known cytokines were examined for a IL-2RIF activity; however, none of cytokines examined exerted a similar activity. Moreover, the neutralizing antibodies against the known cytokines tested did not block the IL-2RIF activity in the SN. When TH1 clones were stimulated with immobilized anti-CD3 or with fixed B cell APC in the presence of partially purified IL-2RIF, these clones expressed IL-2R and showed IL-2-dependent proliferation, whereas they induced neither IL-2R expression nor proliferation in the absence of IL-2RIF activity. These observations suggest that IL-2RIF activity is mediated by a novel cytokine(s) and the cytokine plays an important role as a second signal in the activation of the TH1 clone.

Impaired delayed-type hypersensitivity response in mutant mice secreting soluble CD4 without expression of membrane-bound CD4

Delayed‐type hypersensitivity (DTH) is an important in vivo manifestation of cell‐mediated immunity. We examined the DTH response to methylated bovine serum albumin of a novel mutant strain of mice that have soluble CD4 (sCD4) in their circulation without expression of CD4 on the cell surface. The DTH response of the mutant mice was severely impaired, although the response of CD4 knockout (KO) mice, generated by homologous recombination, was comparable to that of wild‐type mice. The response of the mutant mice was restored by the neutralization of sCD4 with anti‐CD4, and that of CD4KO mice was markedly reduced by the implantation of a diffusion chamber containing sCD4 cDNA transfectant cells. The restored DTH response of the mutant mice treated with anti‐CD4 was abolished by treatment with anti‐interferon‐γ (IFN‐γ). IFN‐γ production by CD4 mutant and CD4KO mice was consistent with their DTH response and inversely related to the presence of sCD4 in their circulation, indicating that sCD4 impairs the DTH response by blocking the production of IFN‐γ in our mutant mice. These results raise the possibility that sCD4 could impair cell‐mediated immunity. Our mutant mice would provide a useful tool with which to analyse the mechanisms of the DTH reaction.