We showed that CD127 downmodulation in the BM was retained in mice lacking IL-7 but not in those lacking either IL-15 or IL-15Rα. In IL-7 KO mice, the difference in CD127 membrane expression between spleen and BM CD44high CD8+ T cells was even more pronounced than in normal mice, possibly due to the severe lymphopenia and the relative increased Ivacaftor manufacturer availability of cytokines other than IL-7 for the remaining T cells. As regards IL-15- and IL-15Rα-KO mice, there was no CD127 difference among

spleen, LNs, and BM in IL-15Rα KO mice, whereas CD127 membrane expression was even higher in the BM compared with that in spleen and LNs in IL-15 KO mice. Separate analysis of CD122high and CD122int/low cells revealed that the normal CD127 downmodulation in the BM was always impaired in both KO strains; in the case of CD122int/low cells, CD127 expression was again higher in the BM than in spleen and LNs only in IL-15 KO mice. Subtle differences between the two KO strains were observed also in other contexts [[26, 29, 34]]. More importantly, after adoptive

transfer of conventional WT CD44high CD8+ T cells into either IL-15 or IL-15Rα KO mice, CD127 membrane expression was similar in the spleen, LNs, and BM of recipient mice and no differences were observed between the two KO strains. It might be unexpected that CD127 downmodulation by CD122int/low cells in the BM was lost in both IL-15- and IL-15Rα-KO mice, as these cells are usually considered IL-15-independent and are RAS p21 protein activator 1 certainly less responsive to IL-15 than CD122high cells. Still, purified WT CD44high CD122int/low cells display a weak proliferative response to IL-15 in vitro [[27]] this website and it is possible that in

normal mice the CD122int/low subset comprises cells that downregulated their CD122 in vivo, probably in response to IL-15 [[28]]. Interestingly, immunofluorescent staining of human BM sections demonstrated close contacts between CD8+ T cells and IL-15-producing cells, comprising both myeloid and stromal cells [[35]]. Moreover, BM CD11c+ dendritic cells (DCs) had higher expression of membrane IL-15 as compared with that of spleen CD11c+ DCs from BALB/c mice [[36]]. In further studies, we will approach the role played by DCs in our system by generating IL-15 KO mice in which IL-15 gene expression is restored only in CD11c+ cells (under investigation). The reduced CD127 expression in the BM could lead to impaired IL-7 responsiveness, in agreement with our previous data showing that freshly purified CD8+ T cells from the BM had a lower proliferative response to IL-7, but not to IL-15, as compared with their spleen counterparts [[11]]. Such IL-7 in vitro results are in contrast with in vivo findings by us and others, showing that under physiological conditions both total CD8+ and memory CD8+ T cells have a higher proliferation in the BM as compared with corresponding cells in spleen and LNs [[10-12]].