Murine NKT cells produce Th17 cytokine interleukin-22

Natural killer T (NKT) cells are known to produce Th17 cytokine IL-17 in addition to Th1/2 cytokines. In this study, the ability of NKT cells to produce IL-22, another Th17 cytokine, was examined in mice. When murine spleen cells were stimulated with α-galactosyl ceramide, a ligand for NKT cells, not only Th1/2 cytokines (IFN-γ, IL-4) but Th17 cytokines (IL-17, IL-22) were produced. NKT cells isolated from splenocytes released IL-17 and IL-22 following CD3, CD3/IL-2 or CD3/CD28 stimulation, in which CD3/CD28 costimulation was most effective. Production of IL-17 and IL-22 in CD4+ and CD8+ T cells from splenocytes was little, if any, even after CD3/CD28 costimulation. Treatment with IL-6/TGF-β decreased CD3/CD28-stimulated production of IL-22, but not that of IL-17, in NKT cells. These findings show for the first time that NKT cells are a cell source of IL-22, and that expression of two Th17 cytokines might be regulated in NKT cells by different mechanisms.     

Synergistic effect of IL-2, IL-12, and IL-18 on thymocyte apoptosis and Th1/Th2 cytokine expression

In the periphery, IL-18 synergistically induces the expression of the Th1 cytokine IFN-gamma in the presence of IL-12 and the Th2 cytokines IL-5 and IL-13 in the presence of IL-2. Although the expression of these cytokines has been described in the thymus, their role in thymic development and function remains uncertain. We report here that freshly isolated thymocytes from C57BL/6 and BALB/c mice stimulated in vitro with IL-2-plus-IL-18 or IL-12-plus-IL-18 produce large amounts of IFN-gamma and IL-13. Analysis of the thymic subsets, CD4(-)CD8(-) (DN), CD4(+)CD8(+), CD4(+)CD8(-), and CD4(-)CD8(+) revealed that IL-18 in combination with IL-2 or IL-12 induces IFN-gamma and IL-13 preferentially from DN cells. Moreover, DN2 and DN3 thymocytes contained more IFN-gamma(+) cells than cells in the later stage of maturation. Additionally, IL-18 in combination with IL-2 induces CCR4 (Th2-associated) and CCR5 (Th1-associated) gene expression. In contrast, IL-18-plus-IL-12 specifically induced CCR5 expression. The IL-2-plus-IL-18 or IL-12-plus-IL-18 effect on IFN-gamma and IL-13 expression is dependent on Stat4 and NF-kappaB but independent of Stat6, T-bet, or NFAT. Furthermore, IL-12-plus-IL-18 induces significant thymocyte apoptosis when expressed in vivo or in vitro, and this effect is exacerbated in the absence of IFN-gamma. IL-12-plus-IL-18-stimulated thymocytes can also induce IA-IE expression on cortical and medullary thymic epithelial cells in an IFN-gamma-dependent manner. Thus, the combination of IL-2, IL-12, and IL-18 can induce phenotypic and functional changes in thymocytes that may alter migration, differentiation, and cell death of immature T cells inside the thymus and potentially affect the Th1/Th2 bias in peripheral immune compartments.     

Constitutive expression of CIITA directs CD4 T cells to produce Th2 cytokines in the thymus

We generated mice expressing a human type III CIITA transgene (CIITA Tg) under control of the CD4 promoter to study the role of CIITA in CD4 T cell biology. The transgene is expressed in peripheral CD4 and CD8 T cells, as well as in thymocytes. When CD4 T cells were differentiated towards the Th2 lineage, both control and CIITA Tg Th2 cells expressed similar levels of Th2 cytokines. Th1 cells from control and CIITA Tg mice cells produced comparable levels of IFN-gamma. CIITA Tg Th1 cells also expressed IL-4, IL-5, and IL-13 in the absence of Stat6. There was an approximate 10-fold increase in the number of peripheral na?ve CD4 T cells and NK1.1- thymocytes producing IL-4 from CIITA Tg mice compared to control mice. Finally, Th1 cells from irradiated control mice reconstituted with CIITA Tg bone marrow displayed the same cytokine production profiles as Th1 cells from CIITA Tg mice. Together, our data demonstrate that CIITA expression pre-disposes CD4 T cells to produce Th2 type cytokines. Moreover, phenotypic similarities between Th1 cells expressing the CIITA transgene and CIITA deficient Th1 cells suggest that the role of CIITA in cytokine regulation is complex and may reflect both direct and indirect mechanisms of T cell development and differentiation.     

Suppression of early IL-4 production underlies the failure of CD4 T cells activated by TLR-stimulated dendritic cells to differentiate into Th2 cells

Dendritic cells (DCs) activated through TLRs provide a potent negative signal for Th2 cell development that is independent of positive signals for Th1 cell development such as IL-12 and IFN-gamma. In this study we demonstrate that the ability of TLR-activated DCs to suppress Th2 cell development is Ag dose-independent and unique to DCs that have been activated through TLRs vs by cytokines. We show that TLR-activated DCs inhibit early IL-4 production by CD4 T cells and thus inhibit their ability to subsequently increase GATA-3 expression and commit to the Th2 lineage. This occurs independently of expression of the GATA-3 antagonist T-bet. Although CD4 T cells activated by TLR-activated DCs make IL-2, they are not capable of phosphorylating STAT5 in response to this cytokine. This inhibition of responsiveness to IL-2 appears to underlie the failure to make early IL-4. Our findings suggest that DCs provide instructional signals for T cell differentiation before cytokine-mediated Th cell selection and outgrowth.