Age-related changes in circannual rhythms of lymphocyte blastogenic responses in mice

Abstract

Blastogenic responses to T- and B-lymphocyte mitogens were tested in suspensions of splenocytes from 15- and 24- to 28-mo-old C57BL/6 mice and compared with analogous responses in young animals. The mice were housed under constant environmental conditions with alternating light-dark cycles (LD 12:12). Single cell suspensions were cultured in vitro with mitogens, and the induced incorporation of tritiated thymidine by dividing cells was determined. Increases in periodicity of responses to concanavalin A and phytohemagglutinin by T cells and to lipopolysaccharide by B cells and lower mean levels of activation characterized rhythms in cells from 15-mo-old and senescent mice compared with young animals. Amplitudes of the rhythms were unchanged at 15 mo, but by 24 mo of age rhythmic responses of T but not B cells were damped. The separable effects of age on expression of circannual rhythms by T and B lymphocytes suggest another mechanism for imbalance in the immune system. Phases of depressed responses that are extended for several months in populations of older mice could provide increased opportunities for environmental assaults.