Abstract
We examined the proliferative and cytokine-producing activities of CD4+ T cells from young mice of the senescence-accelerated mouse strain SAMP1, which had shown markedly low T-dependent antibody-producing responses. When splenic T cells were cultured with concanavalin A (Con A), the percentage of CD4+ cells decreased earlier in SAMP1 than in C3H/He mice. At 40 hr of culture, the percentage of BrdU-labelled proliferating CD4+ cells increased strongly in C3H/He, but only slightly in SAMP1. When purified CD4+ T cells were cultured with Con A, the percentage of 5-bromo-2'-deoxyuridine (BrdU)-labelled cells peaked at around 48 hr of culture in both strains, but decreased significantly at 64 hr in SAMP1. The production of interleukin (IL)-2 but not IL-4 or interferon-gamma (IFN-gamma) was significantly lower in SAMP1 than in C3H/He at 48 hr of culture. IL-2 production was also markedly low in SAMP1, even under the stimulation of anti-CD3 with anti-CD28 antibodies. The frequency of cells producing IL-2 was significantly lower in SAMP1 than in C3H/He at 6-24 hr of culture with Con A. The percentage of annexin-positive and propidium iodide (PI)-negative apoptotic cells was significantly higher in SAMP1 than in C3H/He at 96 hr of culture. Exogenous IL-2 prevented the decrease in BrdU-labelled cells and the increase in apoptotic cells in the SAMP1 cell culture. These results indicate that SAMP1 CD4+ T cells cannot produce IL-2 at levels sufficient to support cell proliferation and survival. This may account for the weak T-dependent antibody response in SAMP1 mice.