The bone marrow has been known to be a source of
IL-7 in vivo.36 We therefore examined the possibility that there was preferential accumulation of CD45RA+ CD27− CD4+ U0126 T cells of a particular specificity in this lymphoid compartment. First we compared the distribution of CD4+ CD45RA/CD27 subsets in paired blood and bone marrow samples from healthy donors and observed a significant increase in the percentage of CD45RA− CD27− and CD45RA+ CD27− CD4+ T cells in the bone marrow compared with the blood of the same individuals (Fig. 7a). We investigated next whether the specificity of T cells in the bone marrow was similar to that found in the blood of the same individuals (Fig. 7b). We found that the increased proportion of CMV-specific CD4+ T
cells relative to other populations was also observed in bone marrow see more samples, indicating that the inflation of CMV-specific T cells occurs in more than one lymphoid compartment in vivo (Fig. 7b). In addition, the proportion of CMV-, VZV- and EBV-specific CD4+ T cells was not significantly different between the two compartments. However, there were significantly more PPD-specific CD4+ T cells in the bone marrow compared with the peripheral blood from the same donors, although the significance of this is not clear at present. We next investigated whether there was preferential accumulation of CD45RA− CD27− and CD45RA+ CD27− CD4+ T cells of a particular specificity in the bone marrow. We found that the proportion of CMV-, VZV-, EBV- and PPD-specific populations in the bone marrow that were CD45RA− CD27− and CD45RA+ CD27− was not different to that in the blood of the same individuals
(Fig. 7c). Therefore it appears that CD45RA− CD27− and CD45RA+ CD27− T cells of all specificities have equal propensity to accumulate in the bone marrow and that it is not a unique site for the generation of CMV-specific effector/memory CD4+ T cells. In this study we show that whereas persistent CMV infection is mainly responsible for the increase of CD45RA− CD27− and CD45RA+ CD27− CD4+ click here T cells in older subjects, both ageing as well as CMV infection contribute to the decrease of CD45RA+ CD27+ CD4+ T cells. This latter observation may reflect the impact of thymic involution compounded with persistent CMV infection during ageing.1 The majority of CD45RA− CD27− and CD45RA+ CD27− populations in CMV-infected subjects are CMV-specific but there are also increased numbers of these effector CD4+ cells that are specific for other viruses, i.e. EBV, HSV and VZV. This suggests that CMV infection may drive a global increase in CD4+ T-cell differentiation suggesting a bystander phenomenon. However, we cannot rule out the possibility that some people are particularly susceptible to the reactivation of latent viruses in general, CMV included.