Immune response against the T-independent antigen alpha (1 leads to 3) dextran. I. Demonstration of an unexpected IgG response of athymic and germ-free-raised euthymic BALB/c mice.

The primary antibody response in BALB/c mice to the T-independent bacterial antigen dextran B1355S [alpha(1 leads to 3)dextran] (Dex) was studied by means of isoelectric focusing, hemagglutination and immunodiffusion techniques. In response to a single immunization with 10 micrograms Dex all mice produce specific IgM antibodies. In addition, about 30% of conventionally raised BALB/c and BALB/c nu/ + mice, but 95% of germ-free (GF)-raised normal BALB/c and 100% of athymic BALB/c nu/nu mice produce specific IgG class anti-Dex antibodies. These antibodies include all IgG subclasses, carry predominantly the lambda light chain and the cross-reactive J558 idiotype and are specific for the alpha(1 leads to 3)glucosidic linkage. As compared to athymic and GF-raised mice, conventionally raised mice exhibit only a weak IgG response. The pronounced IgG production of GF-raised mice was not altered when adult mice were removed from their GF environment and housed under conventional conditions for several weeks prior to immunization with Dex. Reconstitution with isolated splenic T cells from conventionally raised, unprimed BALB/c mice reduces the remarkable capacity of BALB/c nu/nu mice to produce IgG anti-Dex antibodies. These findings suggest that the reduced capacity of conventionally raised BALB/c mice to mount an IgG response to the T-independent antigen Dex is due to a T cell-mediated suppressive mechanism which is neonatally induced by contact with environmental, i.e. bacterial, antigens.