Mucosal Immunologic Responses in Cholera Patients in Bangladesh

Abstract

Vibrio cholerae O1 causes dehydrating diarrhea with a high mortality rate if untreated. The infection also elicits long-term protective immunity. Since V. cholerae is noninvasive, mucosal immunity is likely important for protection. In this study, we compared humoral immune responses in the duodenal mucosa and blood of cholera patients at different time points after the onset of disease and compared them with those of healthy controls (HCs). Immune responses to lipopolysaccharide (LPS) and the recombinant cholera toxin B subunit (rCTB) were assessed by enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immunospot (ELISPOT) assay. Significant increases in V. cholerae LPS-specific IgA and IgG antibody levels were seen in duodenal extracts on day 30, but the levels decreased to baseline by day 180; plasma V. cholerae LPS-specific IgA levels remained elevated longer. Levels of mucosal CTB antibodies also peaked on day 30, but the increase reached statistical significance only for IgG. A significant correlation was found between the CTB antibodysecreting cell (ASC) response in the circulatory system on day 7 and subsequent CTB-specific IgA levels in duodenal extracts on day 30 and the numbers of CTB-specific IgA ASCs in duodenal tissues on day 180. The proportion (0.07%) of mucosal V. cholerae LPS IgA ASCs peaked on day 30 and remained elevated through day 180 compared to that of HCs (P ‫؍‬ 0.03). These results suggest that protective immunity against V. cholerae is not likely mediated by the constitutive secretion of antibodies at the mucosal surface; our results are consistent with those of other studies that suggest instead that anamnestic immune responses of mucosal lymphocytes may play a major role in protection against cholera.

Comparison of Immune Responses to the O-Specific Polysaccharide and Lipopolysaccharide of Vibrio cholerae O1 in Bangladeshi Adult Patients with Cholera

“…The immune response at the surface of the gut is believed to play a critical role in mediating protection from cholera, and previously infected patients may have an anamnestic immune response by mucosal lymphocytes (1,47). After initial interaction with pathogen, antigen-specific lymphocytes from the gut can be transiently detected in the circulation while in transit to other mucosal organs.…”

“…Although the vibriocidal response is currently the most used marker of immunity to cholera, it is believed to be a surrogate marker for another yet to be fully defined immune response at the mucosal surface (10,43). In previous studies, we have shown that there are significant IgA antibody-secreting cells specific for LPS in duodenal biopsy specimens of patients out to day 180 after infection, suggesting a persisting mucosal immune response to this antigen (47). Furthermore, following cholera, patients develop a circulating memory B-cell response to LPS that persists out to days 180 to 270 after infection but wanes by 1 year postinfection.…”

Rapid Effects of a Protective O-Polysaccharide-Specific Monoclonal IgA on Vibrio cholerae Agglutination, Motility, and Surface Morphology

“…Although there is mounting evidence that OPS-specific IgA antibodies are the primary contributor to mucosal immunity against V. cholerae, the mechanisms by which these antibodies interfere with V. cholerae's ability to colonize the intestinal epithelium remain poorly understood (3,9,(17)(18)(19)35). In this study, we examined the interaction between V. cholerae O395 and 2D6, a murine polymeric IgA MAb directed against the nonreducing terminal residue of Ogawa OPS (11,12,25).…”

“…Others have confirmed the importance of LPS-specific IgA in interfering with V. cholerae colonization of the intestinal epithelium in the neonatal mouse model and with tissue section overlay assays (13-16). LPS-specific fecal IgA levels are also implicated as a primary correlate of immunity to V. cholerae in humans (3,(17)(18)(19).Despite the evidence that LPS-specific IgA antibodies play a central role in protective immunity to V. cholerae, it is still not clear how they impede the ability of the bacterium to colonize the intestinal epithelium. IgA is not vibriocidal, nor does it promote Fc-mediated uptake of opsonized bacteria in the intestinal lumen (12).…”

“…Others have confirmed the importance of LPS-specific IgA in interfering with V. cholerae colonization of the intestinal epithelium in the neonatal mouse model and with tissue section overlay assays (13)(14)(15)(16). LPS-specific fecal IgA levels are also implicated as a primary correlate of immunity to V. cholerae in humans (3,(17)(18)(19).…”