Anti-Ia serum blocking of macrophage function in the in vitro humoral response.

Antisera directed at I-region gene products coded for by genes in the I-J subregion effectively block macrophage function in the primary in vitro response to burro erythrocytes. Pretreatment of macrophages with normal serum, nonappropriate anti-Ia antibodies, or anti-H-2 serum had no inhibitory effect. Similar antiserum pretreatment of macrophage-depleted cells did not affect their ability to function with untreated adherent splenic macrophages. The results suggest that the Ia molecule has an active role in antigen presentation by the macrophage or in macrophage-lymphocyte interaction in the primary IgM response.