Age‐Dependence of the IgA Anti‐α(1→3) Dextran B1355 Response in Vitro

The magnitude of the Balb/c mouse IgA anti‐α(1→3) dextran B1355 (anti‐dex) response in vivo was recently found to be markedly T‐cell‐dependent and age‐dependent. This report demonstrates that the in vitro IgA anti‐dex response by mesenteric lymph nodes (MLN) is highly age‐dependent and that there is an age‐dependent increase of the background IgA anti‐dex plaque‐forming cell (PFC) response occurring in the absence of added antigen which correlates significantly with the magnitude of the antigen‐stimulated response. In aging mice both background and antigen‐stimulated IgA anti‐dex responses appeared to be significantly higher in MLN than in spleen cultures. Moreover, it is shown that there is a striking increase with age of natural antibody in the serum of normal Balb/c to α(1→3) film‐in determinants, particularly IgA and lesser amounts of IgM and IgG3.