Diseases associated with aging are now the primary causes of death in
developed countries. This is in part due to the long recognized expone
ntial association of cancer with age and perhaps to a deterioration of
the immune system with advanced age. Both prevention of tumorigenesis
and immune function are critically dependent on apoptosis. In this st
udy we examined apoptosis in mice of various age following gamma irrad
iation. We found a striking age-dependent decrease in radiation-induce
d apoptosis in splenic lymphocytes but not in colorectal epithelial ce
lls. These observations may therefore provide a clue to the decline of
immune function with age.