Age-related increases in mitogenic responses and natural immunity to a syngeneic fibrosarcoma in rats

An increase in natural (innate) immunity with age (through 65 weeks) of NBR rats to a syngeneic methylcholanthrene-induced fibrosarcoma (MCA) is described. This increase is characterized by the appearance of spontaneous tumor regressor animals and an increase in the incidence of tumor non-takes by rats 45 weeks of age and older when compared to younger animals. Age-related changes were observed in the in vitro proliferative responses of normal unfractionated and nylon wool fractionated spleen cells to Con A, PHA and irradiated MCA tumor cells. Certain of these different proliferative responses either increased and/or decreased independently at different ages. Relative to normal spleen cell proliferative responses, tumor progressors have decreased proliferative responses and tumor regressors display increased proliferative responses. The significance of this in light of current aging research is discussed.