Cholera holotoxin and its B subunit enhance Peyer's patch B cell responses induced by orally administered influenza virus: disproportionate cholera toxin enhancement of the IgA B cell response

In these studies we analyzed the adjuvant effect of cholera holotoxin or cholera toxin (CT) B subunit on the B cell response to mucosal antigens. Purified Peyer's patch B cells obtained from mice at varying periods of time after oral administration of inactivated influenza virus, with or without a CT preparation, were stimulated in vitro in the absence or presence of various lymphokines. Responses were measured by an antigen- and isotype-specific ELISPOT assay. In this system cultures containing a combination of lymphokines [interleukin 5 (IL 5), interferon-gamma (IFN-gamma), IL 4] gave comparable responses to those containing T cells from immunized mice or supernatant of concanavalin A-stimulated T cells and therefore were assumed to express optimum or near optimum B cell responses. Administration of a CT preparation along with influenza virus increased the number of B cells producing anti-influenza antibodies of both the IgM and IgA isotypes, with the effect on the IgA response at least threefold greater than the effect on the IgM response. These results thus indicate that CT preparations enhance the memory B cells response in Peyer's patches and, in addition, suggest that CT enhances isotype switching. In this antigen-specific B cell system IL 4 augmented responses in cultures containing IL 5 but not IFN-gamma; in addition, IL 5 and IFN-gamma acted in an additive fashion. Thus, these findings suggest that the effects of IL 5 and IFN-gamma are at least in part, mediated via different cellular differentiation pathways.