Effects of age on cellular immune responses in BALB/cJ mice: Increase in antibody-dependent T lymphocyte mediated cytotoxicity

Two in vitro cell-mediated immune (CMI) responses of splenic lymphocytes of BALB/cJ mice of various ages (1.25, 2.5, 4, 10.5 and 30 months) were examined. These were the antibody-dependent lymphocyte-mediated cytotoxicity (ADLMC) responses, mediated by the K cell subclass of T lymphocytes, and phytohemagglutinin (PHA) induced mitogenesis, mediated by the theta (θ) positive T lymphocytes. ADLMC responses increased with age, culminated at 10.5 months, then slowly declined. Lymphocytes of young mice (2.5 or 4 months of age) were significantly more responsive to PHA than lymphocytes of mature (10.5 months) or aged adults (30 months) (p < 0.01), indicating progressive suppression of this type of CMI response with age, as observed previously. The difference in time of maturation and extent of suppression of ADLMC and PHA responses was not influenced by changes in numbers of specific effector cells, since percentages of these did not change with age (as measured by immunofluorescence and rosetting techniques). The increase with age of ADLMC responses may be due to deregulation of earlier suppressor activity which allows the K cell to be fully responsive, but other mechanisms may be involved.