Temporal order vs. variability in activation of lymphocytes from aging mice

Changes in patterns of circannual rhythms in the in vitro activation of splenic lymphocytes from aging C57BL/6 mice may account both for reports of conflicting results in tests of immune function and for the assumed increase in variability in data obtained using cells from older mice. Single cell suspensions from 4-6, 15 and 24-28-month-old mice living in presumably constant environments were cultured in vitro with mitogens, and the incorporation of tritiated thymidine by dividing cells was determined. Free-running periods of T and B lymphocyte rhythms of blastogenic responses increased in cells from both older groups; amplitudes of the T but not B cell rhythms were reduced in senescent mice. This results in continuously changing phase relationships of both T and B cell rhythms, without consistently higher levels of activation of cells from young animals, thus obscuring at intervals the age-related declines in function. Because data were collected for several years, it was clear from the patterns of the rhythms and also the combined data that the greatest ranges in levels of activation ("variability") characterized T and B cells from the youngest mice rather than older animals.