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.

Aerobic training increases the stimulated percentage of CD4+CD25+ in older men but not older women

“…2, 3), in agreement with others (Brock 1987;Pati et al 1987). As with seasonal changes in leukocyte concentration, the changes in CD25 expression may be due to seasonal variations in cortisol, melatonin and prolactin production (Brock 1987;Maes et al 1997), and suggest that March-April is a period of reduced lymphocyte responsiveness and proliferation, while August-September and January are periods of increased lymphocyte responsiveness.…”

“…2, 3), in agreement with others (Brock 1987;Pati et al 1987). As with seasonal changes in leukocyte concentration, the changes in CD25 expression may be due to seasonal variations in cortisol, melatonin and prolactin production (Brock 1987;Maes et al 1997), and suggest that March-April is a period of reduced lymphocyte responsiveness and proliferation, while August-September and January are periods of increased lymphocyte responsiveness. Others have also reported an increase in PHA lymphocyte proliferative responses from September to November (Pati et al 1987), and deWnite seasonal variations in both T and NK cell function (Brock 1987;Maes et al 1994).…”

“…We were not able to measure cortisol concentration during the study, but we found that CD4 + lymphocyte concentration decreased for all groups during April and again during late September, in agreement with others (Brock 1987;Maes et al 1994;Mann et al 2000), suggesting that individuals might be at more risk of infection during these months.…”

“…Moderate intensity training did not increase CD25 density in either the male or female group post-study, but we did Wnd signiWcant sequential monthly changes in both percentage of CD4 + CD25 and CD25 density during the study for male and female UT and TR groups, which suggest that there may be seasonal variations in CD25 + expression. Seasonal decreases in mitogenic responsiveness and CD25 expression may be associated with increased risk of infection during these seasons (Brock 1987).…”

“…Monthly and seasonal changes in leukocyte concentration have been attributed to seasonal changes in cortisol, prolactin and melatonin concentration (Brock 1987;Maes et al 1994Maes et al , 1997, with increased cortisol production inversely related to leukocyte concentration.…”