STIMULATION OF THE SAME B-CELL POPULATION BY THYMUS-INDEPENDENT DEXTRAN AND BY THYMUS-DEPENDENT OLIGOSACCHARIDE-CARRIER

The immune response of adult BALB/c mice against the bacterial antigen dextran B1355S (Dex) is well characterized as thymus independent (TI type 2) and Igh(a) linked. The antisera consist of mainly IgM/lambda a ntibodies directed against the alpha(1-->3) glucosidic linkage. This s tudy describes the immune reponse against the alpha(1-->3) linkage in the thymus dependent form (TD), i.e. tetra- or heptasaccharides (N4 or N7) of glucose as hapten coupled to chicken serum albumin (CSA) as ca rrier. Whereas athymic BALB/c-nu/nu mice did not respond to the TD ant igens N4-CSA and N7-CSA, euthymic BALB/c showed high anti-Dex antibody titres of IgM and, after 2 degrees immunization, a class switch to Ig G (mainly IgG1) isotypes with lambda light chains. The hapten N4 inhib ited Dex-binding of M104E or of antisera from Dex or N4-CSA or N7-CSA immunized mice at 1.7-10 x 10(-4) M. The idiotype composition of these antibodies resembled those after Dex immunization. We conclude that t he same Dex-specific precursor B cells have been stimulated by either form of antigen. The ontogenic development of a Dex-specific response could not be accelerated by the aid of T cells, even of adult origin. It seems, therefore, that the maturation of antigen specific B cells i s the limiting step in ontogeny.