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 B13558 (Dex) is well characterized as thymus independent (TI type 2) and Igh a linked. The antisera consist of mainly IgM/ antibodies directed against the λ(1 → 3) glucosidic linkage. This study describes the immune reponse against the α(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 carrier. Whereas athymic BALB/c‐nu/nu mice did not respond to the TD antigens N4‐CSA and N7‐CSA, euthymic BALB/c showed high anti‐Dex antibody titres of IgM and, after 2° immunization, a class switch to IgG (mainly IgGl) isotypes with λ light chains. The hapten N4 inhibited Dex‐binding of M104E or of antisera from Dex or N4‐CSA or N7‐CSA immunized mice at 1.7–10 × 10 4 M. The idiotype composition of these antibodies resembled those after Dex immunization. We conclude that the 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 is the limiting step in ontogeny.