Intraperitoneal delivery of cholera toxin B subunit enhances systemic and mucosal antibody responses

Although cholera toxin (CT) is a potent mucosal adjuvant, its activity in systemic immunity is relatively undocumented. In the present study, we investigated its adjuvant effect on systemic and mucosal antibody responses following intraperitoneal immunization of mice with BSA. CT increased levels of anti-BSA specific IgG1, IgM, and IgA antibodies in the peritoneum and serum, as well as IgA and IgG1 antibodies in the intestinal fluids. The B subunit of CT (CTB) was as potent as CT itself, with potency comparable to that of incomplete Freund's adjuvant. CTB also increased the number of BSA-specific Ig secreting cells in the spleen and mesenteric lymph node, and stimulated expression of B7.2 but not of MHC class II molecules on peritoneal macrophages, particularly in the presence of IFN-gamma. Our results imply that intraperitoneally administered CTB enhances systemic and mucosal antibody responses, in part at least via effects on macrophages.