The heterogeneity of the age-related decline in immune response: Impairment in delayed-type hypersensitivity and cytotoxic T-lymphocyte activity occur independently

Abstract

Aged mice are known to have a heterogeneous cytotoxic T-lymphocyte (CTL) response to an influenza challenge. We sought to determine whether delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) was also heterogeneous in aging and, if so, whether this correlated with anti-influenza CTL activity. Aged mice developed mean footpad swelling of 0.24 ± 0.09 mm following SRBC challenge and mean CTL activity of 35 ± 18%. Even though these values were significantly lower than those from young mice (0.54 ± 0.10 mm and 51 ± 2%, respectively), no correlation was found between anti-influenza CTL activity and DTH to SRBC ( r = 0.01). We believe the most likely reason for this independent decline in immune response is because different activation signals are required for DTH and CTL activity. Our data thus suggest an age-related functional mosaicism in the immune system.