CD45−podoplanin+ SSCL were negative for most leukocyte or non-stromal markers, indicating that they were of stromal origin. In addition to podoplanin, CD45−podoplanin+ SSCL were strongly positive for LTβ receptor, TNF receptor 1, VCAM-1, collagen-I and ERTR7. Interestingly, CD45−podoplanin+ SSCL expressed mRNA for the T-zone chemokine CCL19 but not CCL21. Although expression of BP-3 was not detected by immunofluorescence, expression at the mRNA level was detected by quantitative PCR (data not shown). CD45−podoplanin+

SSCL were negative for the vascular endothelial marker CD31 and lymphatic endothelial marker Prox1. Furthermore, they were negative for Foxn1, an epithelial marker, suggesting that CD45−podoplanin+ SSCL are stromal cells GPCR Compound Library ROCK inhibitor of fibroblastic origin. Collectively, these data suggested that CD45−podoplanin+ SSCL display many of the phenotypic features of splenic white pulp T-zone stromal cells. Link et al. have recently described TRC as the only stromal cell subset in LN capable of keeping T cells alive though IL-7 and CCL19 17. To test whether the CD45−podoplanin+ SSCL behave like TRC functionally, their ability to support

T-lymphocyte survival was investigated. T- or B-lymphocytes from the spleen of WT mice were purified by FACS (99±0.5%) and cultured on an adherent monolayer of CD45−podoplanin+ SSCL. After 4 days co-culture, 16±2% of the T cells were still alive when cultured with stroma, compared with less than 2% of T cells cultured without stroma and there was no survival of B cells co-culture with stroma (Fig. 2E). We have previously shown that adult

LTi-like cells interact with T-zone stromal cells 6. To investigate whether the CD45−podoplanin+ SSCL were also able to support adult LTi-like cell survival, we cultured adult LTi-like cells with Aspartate CD45−podoplanin+ SSCL. After 4 days co-culture, almost all the hematopoietic cells surviving in culture were adult LTi-like cells (data not shown). Their survival was significantly better than that of adult LTi-like cells cultured in media alone. Although culture with recombinant IL-7 improved adult LTi-like cell survival, it was significantly less than that achieved with CD45−podoplanin+ SSCL co-culture (Fig. 3A). Since T-zone stroma isolated from the adult LN maintains T-cell survival in vitro through IL-7 17 and the CD45−podoplanin+ SSCL express IL-7 mRNA (Supporting Information Table 1), we wondered whether adult LTi-like cell survival in vitro might also be mediated by IL-7. Anti-IL-7 blocking antibodies that significantly inhibited recombinant IL-7-mediated survival, had no significant effect on LTi-like cells co-cultured with CD45−podoplanin+ SSCL (Fig. 3B). Furthermore, 60±6.3% of LTi-like cells survived when cultured with the splenic stromal cells versus 25±2.4% when cultured with recombinant IL-7 alone (data not shown).