CD8+ T cells are vital for the control and clearance of intracellular pathogens. Activation of naïve T cells initiates a program of proliferation and differentiation resulting in the acquisition of lineage-specific effector functions. Following the clearance of infection, the effector cell population contracts, leaving a population of self-renewing memory cells. These cells are capable of rapid expansion and acquisition of effector activity upon secondary infection, providing the basis of T cell mediated immunity.
Recent reports suggest that the bone marrow is a major reservoir for memory T cells. Using influenza infection of B6 mice as a model, we examined both the number and quality of of influenza A virus-specific CD8+ memory T cells isolated from this site. To gain further insight into the function of T cells derived from this tissue, we first demonstrate that transfer of naïve, bone marrow (BM) derived CD8+ OT-I T cells failed to effectively recirculate into the lymph nodes and were short lived compared to lymph node derived naïve OT-I CTL. This may be attributable to the removal of BM cells from their anatomical niche and loss of survival signals. Interestingly, of those naive CTL that did respond to influenza A virus infection, effector CTL were found to have a similar phenotype and function irrespective of where they were derived from. In an analysis of bone marrow derived memory CTL, we showed that while there were significantly larger numbers of resting memory T cells found in the bone marrow compared to other secondary lymphoid tissues, that memory CTL derived from either BM or lymph nodes also showed equivalent phenotypes and function, and were both capable of similar recall responses after secondary infection. Our data are consistent with the notion of the bone marrow serving as a reservoir of CD8+ memory cells, but suggest that aside from their residing in the bone marrow, these cells are functionally indistinguishable from lymph node-derived memory cells.