Role of local IgA antitoxin-producing cells for intestinal protection against cholera toxin challenge

We examined in mice, perorally immunized with cholera toxin (CT) or cholera B subunit (CTB), the association between protection against intestinal toxin challenge and frequency and function of gut mucosal IgA antitoxin-forming cells. The in vitro production of IgA antitoxin by isolated cells and the toxin-neutralizing ability of culture supernatants were determined. Repeated oral immunizations with CT gave rise to high numbers of IgA antitoxin 'spot-forming' cells (SFC) in the lamina propria as well as to protection against challenge with CT in ligated intestinal loops. In contrast, mice immunized with purified CTB, gave poor IgA antitoxin SFC responses in the lamina propria and little or no protection. When a small amount of CT was used to adjuvant the response to CTB, many IgA antitoxin SFC were found; however, protection in intestinal loops remained poor. This discrepancy was explained by the predominant localization of antitoxin SFC in the proximal small intestine following oral CTB/CT-adjuvant immunization, whereas relatively few SFC were found further down in the intestine where the loop-protection test was performed. Thus, when lamina propria plasma cells were isolated from challenged loops and cultured in vitro, they released only low titers of IgA antitoxin and CT-neutralizing antibodies in culture supernatants; this was in contrast to cells from optimally immunized mice which gave supernatants with high IgA antitoxin and toxin-neutralizing antibody titers. Increasing the dose of CT, added as adjuvant to the CTB, resulted in better protection and higher numbers of IgA antitoxin SFC in more distal parts of the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)