Role of Local IgA Antitoxin-Producing Cells for Intestinal Protection against Cholera Toxin Challenge

Abstract

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. We also found that the build-up of strong local immunity in the gut was more dependent on repeated exposures to antigen than on immune maturation over time after oral immunizations. Our findings confirm that intestinal IgA antitoxin formation and protection against toxin challenge after oral immunization with CT are closely correlated, and that this correlation also holds true for CT-adjuvanted CTB administered by the oral route.

Analysis of the roles of antilipopolysaccharide and anti-cholera toxin immunoglobulin A (IgA) antibodies in protection against Vibrio cholerae and cholera toxin by use of monoclonal IgA antibodies in vivo

“…IgA antibodies directed against CT have also been implicated in protection against V. cholerae-induced disease (7,10,16,19), but the relative importance of anti-CT IgA in protection has not been well defined (13,14). In several experimental systems, the presence of anti-CT IgA antibodies in secretions was associated with protection of the intestine against orally administered CT (16-18, 28-30, 37).…”

“…After ingestion, V. cholerae enters the small intestine, adheres to mucosal surfaces, and forms colonies that secrete cholera toxin (CT), the agent responsible for the massive secretory diarrhea that is the hallmark of the disease (7,14,22). Colonization of the intestine by V. cholerae evokes a mucosal immune response in the host, including secretion of immunoglobulin A (IgA) antibodies (sIgA) that are thought to be involved in limiting the duration of the primary infection and in imparting resistance to subsequent oral challenge (10,13,(16)(17)(18)(19)(20)33). This response includes polyclonal sIgA antibodies directed against both CT and bacterial surface components including the outer membrane lipopolysaccharide (LPS) (10,15,19).…”

Monoclonal immunoglobulin A antibodies directed against cholera toxin prevent the toxin-induced chloride secretory response and block toxin binding to intestinal epithelial cells in vitro

“…There is considerable evidence, however, that antitoxin antibodies play the primary role in protection against oral toxin challenge. Polyclonal anti-CTB antibodies have been shown to be capable of toxin neutralization in both rabbit skin permeability tests and ligated intestinal loop models (26,33). Recently, it was demonstrated that protection of intestinal loops against intraluminally injected CT in animals orally immunized with CT is CD4 T cell dependent (14).…”

Protection of rat intestine against cholera toxin challenge by monoclonal anti-idiotypic antibody immunization via enteral and parenteral routes

“…It was demonstrated (24) that even repeated oral immunizations with CT-B devoid of any CT did not induce any significant protection, despite the presence of some anti-CT Ab responses. To obtain significant, but weak, gut protection, the CT-B oral immunizations required the presence of at least 5% CT (24). Hence, the mean degree of intestinal protection observed after our anti-id MAb2 immunizations was indeed remarkable.…”

“…A potential problem with our data could be the lack of correlation (data not shown) between individual serum or biliary anti-CT Ab3 titers, on the one hand, and the percentage of protection against the gut CT challenge in the same animals on the other hand. Such a correlation, which has been obtained with oral immunizations directly with CT or CT-B mixed with traces of CT (24), would nevertheless seem desirable if anti-id vaccination is to become more generally acceptable. On the other hand, when protection was obtained with other anti-id immunization models, correlations between degree of protection and Ab titers were rather poor (29) or not even mentioned.…”