Cytotoxic T lymphocytes (CTL) are crucial for the host defense against viral infection. In many cases, this anti‐viral immune response contributes to host pathogenesis, through inflammation and tissue destruction. Few studies have explored the relative susceptibility of infected cells to CTL killing, and the range of cell types that may be effectively killed by CTLs in vivo, both of which are key to understanding both immune control of infection and immune‐related pathogenesis.

We developed and optimized a highly sensitive method to quantify the relative susceptibility of leukocyte subsets to CTL‐mediated killing. Maximal sensitivity was achieved by uniquely measuring cell death occurring during the assay culture.

We found that leukocyte subsets have a wide range of susceptibility to antigen‐specific CTL‐mediated lysis. Generally, T cells were more susceptible than B or NK cells, with CD4 T cells being more susceptible than CD8 T cells. In all lymphocyte lineages, susceptibility was greater for more differentiated subsets compared with their naïve counterparts; however, for dendritic cells, immature cells are more susceptible than mature cells. We focused on the susceptibility of T cell subsets, and found that naïve cells are far more resistant than memory cells, and in particular, CCR5+ or HLA‐DR+ memory cells are highly susceptible to CTL‐mediated killing.

These results provide an explanation for the observation that certain subsets of CD4 T cells are ablated during chronic HIV infection, and indicate which subsets are most likely to contain the persistent viral reservoir. Published 2007 Wiley‐Liss, Inc.