CD4+ T cells labelled with CFSE were cultured with anti-CD3 antibody (0·5 μg/ml) Fostamatinib chemical structure for 48 or 72 hr (Fig. 2f). At each time-point examined, SD-4+/+ and SD-4−/− T cells showed almost identical patterns of cell division (as reflected from diffusion of CFSE fluorescent intensity).
Similar results were also noted with lower concentrations (0·1 and 0·3 μg/ml) of anti-CD3 antibody (see Supplementary material, Fig. S2). We then examined the effect of SD-4 deletion on the intrinsic response triggered by concanavalin A, wihch activates T cells in a non-specific manner (Fig. 2g). Again, there was no significant change in T-cell proliferation. Hence, lack of SD-4 expression does not alter the intrinsic responsiveness of T cells to TCR-dependent or non-specific Buparlisib stimulation. These features distinguish SD-4 from PD-1 and BTLA, whose respective deletions augment T-cell responses to anti-CD3 stimulation.[20, 21] Using the mixed lymphocyte reaction, we examined the impact of SD-4 deletion on T-cell reactivity in response to allogeneic DC-HIL+ APC (Fig. 3a,b). CD4+ T cells
(varying numbers) isolated from WT or KO C57BL/6 mice were co-cultured with DC (constant number) prepared from BM cells of BALB/c mice. T-cell activation was measured by secreted IL-2 (Fig. 3a) or by proliferation (Fig. 3b). SD-4−/− T cells produced IL-2 at a four-fold greater level and proliferated at a two-fold higher level, respectively, than SD-4+/+ T cells. We next used a defined antigen model of gp100 (melanoma-associated antigen). SD-4 gene deficiency was introduced into the pmel-1 TCR transgenic mice (in which all CD8+ T cells express the same TCR specific to a particular gp100 antigen peptide). With respect to relative proportions of leucocyte sub-populations in lymphoid organs, there was no significant difference between SD-4+/+ and SD-4−/− pmel-1 mice (data not shown). We then assayed the reactivity of T cells to gp100 peptide-loaded APC. Spleen cells isolated from SD-4+/+ or SD-4−/− pmel-1 mice were
stimulated by increasing doses of antigen and measured for proliferation (Fig. 3c). SD-4+/+ pmel-1 spleen cells proliferated and produced IL-2 in response to gp100 antigen in a dose-dependent manner. Similarly, SD-4−/− pmel-1 spleen cells Baricitinib responded to antigen, but with significantly elevated levels (more than twofold greater responses by SD-4−/− pmel-1 T cells) at almost every single dose of antigen. To more rigorously examine the impact of SD-4 deletion, BMDC were prepared from WT mice and allowed to stimulate SD-4+/+ or SD-4−/− CD8+ T cells (Fig. 3d). SD-4−/− CD8+ T cells produced greater levels of IL-2 than SD-4+/+ CD8+ T cells (up to twofold), consistent with the previous data (Fig. 3c). As SD-4 is also expressed by DC (unpublished data), we examined the possibility that contaminant APC in the T-cell preparation from KO mice contributed to hyperactivation (Fig. 3a).