Age-associated deficiency in activation-induced up-regulation of telomerase activity in CD4+ T cells.

For lymphocytes, the ability to undergo clonal expansion is crucial for effective immune function. Telomerase activity compensates for telomere erosion during cell division and contributes to the capability of lymphocytes to maintain cellular proliferation. In addition, telomerase activity may have a fundamental role in cell growth and survival. To determine whether age-related immune dysfunction is associated with an abnormality in telomerase activity, we investigated telomerase activity in T cell populations from young adult and aged mice. Our data show that the ability of T cells from aged mice to up-regulate telomerase activity after activation was significantly diminished. This age-related deficiency in telomerase induction is restricted to CD4(+) T cells, as CD8(+) T cells retain the capability to up-regulate telomerase activity. These findings reinforce the notion that age-related immune dysfunction results mainly from impairment of helper T cells, and may have important implications for designing novel means to improve immune responses in aged individuals by enhancing CD8(+) T cell functions, which are crucial in both viral and tumour immunity.