T cell-dependent IgA anti-polysaccharide response in vitro

Abstract

The induction in mice of humoral antibody to purified poly-saccharides, such as dextran B1355, dextran B512 and other bacterial capsular materials, is generally regarded as being thymus independent^1–5, that is, not requiring conventional carrier-specific T-cell help⁶. Such responses are largely immunoglobulin M (IgM), often transient although occasionally cyclic, and there is little evidence of immunological memory^7–11. The selective formation of an IgG response to polysaccharides or haptenated polysaccharides (for example, dextran B512, dinitrophenol (DNP)–FicolI) has also been characterized as thymus independent^12,13. Recent reports have indicated that the murine IgG response to such antigens is restricted largely to the IgG₃ subclass^14,15 although lesser amounts of other IgG subclasses have been reported after stimulation with thymus-independent antigens such as DNP–Ficoll and DNP–Levan^16,17. In the latter study, T cells were shown to influence certain IgG subclass responses to haptens on a thymus-independent carrier¹⁷. Here we report that BALB/c mice produce a substantial IgA anti-α(l,3)dextran B1355 response in vitro that is highly T-cell dependent and age-dependent. This finding represents a significant departure from previous observations and may have particular relevance for mucosal immunity. It also suggests the need for a re-evaluation of the induction and regulation of anti-polysaccharide antibody responses.