Studies on B-cell memory. IV. Effects of lipopolysaccharide on primary and secondary antibody responses to T-independent type-2 (TI-2) antigen in mice

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 Igha linked. The antisera consist of mainly IgM/lambda antibodies directed against the alpha(1-->3) glucosidic linkage. This study describes the immune response 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 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 degrees immunization, a class switch to IgG (mainly IgG1) isotypes with lambda 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 x 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.

The thymus-independent antigen alpha(1-3) dextran elicits proliferation of precursors for specific IgM antibody-producing cells (memory cells), which are revealed by LPS stimulation in soft agar cultures and detected by immunoblot

Single antibody-forming cells (AFC) specific for alpha(1-3) dextran (Dex) from i.p.-immunized BALB/c mice were enumerated in soft agar cultures by blotting on antigen-precoated membranes and subsequent staining via enzyme-coupled anti-IgM antibodies. Short cultures (2 h) revealed AFC as harvested ex vivo, while in long-term cultures (4 days), in the presence of lipopolysaccharide (LPS) as B cell mitogen, cells or colonies developed by differentiation in vitro. Whereas the spleen contained most AFC ex vivo in a sharp-peak response at 4 and 5 days after i.p. injection of Dex in aqueous solution, peritoneal exudate cells (PEC) contained only very few AFC. However, the same PEC population developed Dex-specific cells or colonies after 4 days of culture. The isotype of antibodies was IgM. The frequency of these Dex-specific LPS-inducible precursor cells rose exponentially in the course of the immune response to a broad plateau and was still, 11 weeks after Dex injection, approximately 40-fold higher than in non-immunized mice. Since these cells increased in frequency after antigen injection, and since they could not be detected as AFC during 2 h ex vivo, they were regarded as memory cells. They seemed to be arrested in vivo, but could be induced to differentiation and/or proliferation in vitro. Although these cells had the functional characteristics of memory cells as defined above, they produced anti-Dex antibodies of IgM isotype. Their population might be critical for the protection of the peritoneal cavity against microbial invasion from the intestines, and it may be significant in this context that we could evoke a peritoneal memory cell response only when antigen was injected intraperitoneally, but not intravenously. In athymic BALB/c-nu/nu mice only few of these Dex-specific memory cells were found. It is possible that T cells exert a regulatory influence on this pathway of differentiation.