IN-VIVO AND IN-VITRO STUDY OF THE PRIMARY AND SECONDARY ANTIBODY-RESPONSE TO A BACTERIAL-ANTIGEN IN AGED MICE

One of the most important manifestations of aging in both humans and l aboratory animals is a gradual decline in immune effectiveness. Howeve r, it is not clear as to how general is this decline. We here report t hat aged BALB/c mice showed no decline in the magnitude of the in vivo primary antibody response to phosphorylcholine (PC), an immunodominan t epitope of the Streptococcus pneumoniae R36a (Pn). Often it appeared that aged mice responded better than young syngeneic mice. In contras t, the secondary antibody response had a different profile, with aged mice showing a marked decrease in PC-specific antibody. Further in vit ro studies were conducted in order to determine the cause of the decli ne of the secondary antibody response in aging. We noted that B cells from young and aged donors, either primed or twice immunized with the antigen, when cultured without T cells and in the presence of antigen did not display any significant difference in their antibody response to PC. However, L3T4 cells from aged BALB/c mice, previously immunized twice with Pn, failed to augment the in vitro B cell response as comp ared to L3T4 cells from young mice. Moreover, we found that Lyt 2 cell s from young and aged mice had no regulatory effects on the anti-PC re sponse in vitro. Further in vivo experiments demonstrated that alterat ion of the idiotypic network may not be related to a decline in the se condary antibody response since two injections of the antigen are unab le to elicit an anti-idiotypic antibody response in either young or ag ed mice. These data demonstrate that the decline of the anti-PC respon se after a secondary challenge with Pn is linked to defects in the T c ell compartment.