Activation-induced apoptosis in T cells from young and old Fischer 344 rats

BACKGROUND: Activation-induced apoptosis is believed to limit cell proliferation and eliminate the high number of activated cells during an immune response. METHODS: Activation-induced apoptosis was investigated in splenic T cells isolated from young (6 months) and old (24 months) male Fischer 344 rats. The cells were incubated with anti-CD3, concanavalin A or staphylococcal enterotoxin B (primary stimulus) for 72 h, followed by restimulation with anti-CD3 or concanavalin A (secondary stimulus). Apoptosis was assessed by DNA fragmentation assay and DNA gel electrophoresis. The expression of the apoptotic marker CD95 was analyzed by flow cytometry and the relative levels of CD95 ligand, Bcl-2 and Bax protein were measured by immunoblotting. RESULTS: It was shown that DNA fragmentation was very low in the unstimulated T cells from both young and old rats. However, the level of DNA fragmentation was 45-55% greater in the activated T cells from old rats than in the activated T cells from young rats. The increase in DNA fragmentation was paralleled by an increase in the proportion of cells expressing the CD95 molecule. The proportion of CD95+ cells was approximately 40% higher in T cells from old rats than in T cells from young rats. In addition, it was found that the expression of CD95 ligand and Bax increased and Bcl-2 decreased in the activated T cells from old rats compared to the activated T cells from young rats. CONCLUSION: Our data suggest that the increase in sensitivity of T cells to apoptosis with age may contribute to age-associated immune dysfunction and disorders.