Apoptosis in T-lymphocyte subsets in human immunodeficiency virus-infectedchildren measured immediately ex vivo and following in vitro activation

Phosphatidylserine molecules are translocated to the outer plasma membrane of lymphocytes undergoing apoptosis and can be detected by the binding of f luorochrome-conjugated annexin V, Using the annexin V assay, we examined CD 4 and CD8 T cells from human immunodeficiency virus (HIV)-infected children for apoptosis upon isolation or following in vitro culture, Immediate ex v ivo analysis or overnight culture showed significantly higher levels of apo ptosis in CD8 cells than in CD4 cells. Following culture with the activatin g stimulus phytohemagglutinin or anti-CD3 monoclonal antibody, we observed an increase in the percentage of apoptotic CD4 cells, whereas there was no change in the rate of CD8 cell death. These results demonstrate that in HIV -infected children, CD8 apoptosis may occur at a greater rate than CD4 apop tosis in vivo; greater CD4 depletion may be observed due to more efficient mechanisms for peripheral lymphocyte replacement in the CD8 compartment. Fu rthermore, our data suggest that CD8 lymphocytes may be maximally activated in vivo, a condition which may lead to the exhaustion of CD8-mediated immu nity, These findings clarify the differences between the CD4 and CD8 apopto tic responses to HIV.