Human in vivo-activated CD45R0+ CD4+ T cells are susceptible to spontaneous apoptosis that can be inhibited by the chemokine CXCL12 and IL-2, -6, -7, and -15

The number of T cells that have undergone proliferation after antigen stimulation in vivo must be controlled to prevent excessive accumulation of T cells, autoimmunity, and T cell neoplasia. We describe here that primary human adenotonsillar memory phenotype CD45R0+ CD4+ T cells, but not adenotonsillar naive-phenotype CD45RA+ CD4+ T cells, or peripheral blood naive or memory CD4+ T cells, express high levels of activation-associated antigens CD38, CD69, CD71, and HLA-DR. These in vivo-activated CD45R0+ CD4+ T cells were susceptible to spontaneous and rapid apoptosis in vitro. Apoptosis could not be inhibited by the disruption of Fas-Fas ligand engagement or by the pan-caspase inhibitor ZVAD. Cross-linking of the T cell antigen receptor did not rescue cells from apoptosis. Apoptosis could be partially inhibited by the chemokine CXCL12/SDF-1, by IL-6, and by the IL-2 receptor common γ chain-signaling cytokines IL-2, -7, and -15. Inhibitors of phosphatidylinositol 3-kinase accelerated apoptosis. We conclude that after in vivo activation of CD45R0+ CD4+ T cells, the cells experience a period of intrinsically elevated sensitivity to apoptosis and that multiple external signals control their survival.