Immunity against

ABSTRACTVibrio choleraeO1 causes cholera, a dehydrating diarrheal disease. We have previously shown thatV. cholerae-specific memory B cell responses develop after cholera infection, and we hypothesize that these mediate long-term protective immunity against cholera. We prospectively followed household contacts of cholera patients to determine whether the presence of circulatingV. choleraeO1 antigen-specific memory B cells on enrollment was associated with protection againstV. choleraeinfection over a 30-day period. Two hundred thirty-six household contacts of 122 index patients with cholera were enrolled. The presence of lipopolysaccharide (LPS)-specific IgG memory B cells in peripheral blood on study entry was associated with a 68% decrease in the risk of infection in household contacts (P= 0.032). No protection was associated with cholera toxin B subunit (CtxB)-specific memory B cells or IgA memory B cells specific to LPS. These results suggest that LPS-specific IgG memory B cells may be important in protection against infection withV. choleraeO1.

BackgroundMucosal Associated Invariant T (MAIT) cells are innate-like T cells found in abundance in the intestinal mucosa, and are thought to play a role in bridging the innate-adaptive interface.MethodsWe measured MAIT cell frequencies and antibody responses in blood from patients presenting with culture-confirmed severe cholera to a hospital in Dhaka, Bangladesh at days 2, 7, 30, and 90 of illness.ResultsWe found that MAIT (CD3+CD4−CD161hiVα7.2+) cells were maximally activated at day 7 after onset of cholera. In adult patients, MAIT frequencies did not change over time, whereas in child patients, MAITs were significantly decreased at day 7, and this decrease persisted to day 90. Fold changes in MAIT frequency correlated with increases in LPS IgA and IgG, but not LPS IgM nor antibody responses to cholera toxin B subunit.ConclusionsIn the acute phase of cholera, MAIT cells are activated, depleted from the periphery, and as part of the innate response against V. cholerae infection, are possibly involved in mechanisms underlying class switching of antibody responses to T cell-independent antigens.

h Cholera caused by Vibrio cholerae O1 confers at least 3 to 10 years of protection against subsequent disease regardless of age, despite a relatively rapid fall in antibody levels in peripheral blood, suggesting that memory B cell responses may play an important role in protection. The V. cholerae O1-specific polysaccharide (OSP) component of lipopolysaccharide (LPS) is responsible for serogroup specificity, and it is unclear if young children are capable of developing memory B cell responses against OSP, a T cell-independent antigen, following cholera. To address this, we assessed OSP-specific memory B cell responses in young children (2 to 5 years, n ‫؍‬ 11), older children (6 to 17 years, n ‫؍‬ 21), and adults (18 to 55 years, n ‫؍‬ 28) with cholera caused by V. cholerae O1 in Dhaka, Bangladesh. We also assessed memory B cell responses against LPS and vibriocidal responses, and plasma antibody responses against OSP, LPS, and cholera toxin B subunit (CtxB; a T cell-dependent antigen) on days 2 and 7, as well as days 30, 90, and 180 after convalescence. In all age cohorts, vibriocidal responses and plasma OSP, LPS, and CtxB-specific responses peaked on day 7 and fell toward baseline over the follow-up period. In comparison, we were able to detect OSP memory B cell responses in all age cohorts of patients with detectable responses over baseline for 90 to 180 days. Our results suggest that OSP-specific memory B cell responses can occur following cholera, even in the youngest children, and may explain in part the age-independent induction of long-term immunity following naturally acquired disease. C holera is a severe diarrheal disease that is endemic in 50 countries and associated with recurrent outbreaks and epidemics, especially in resource-limited settings (1). Vibrio cholerae can be classified into approximately 200 serogroups, and epidemic cholera can be caused by V. cholerae O1 and O139 serogroups (1, 2). V. cholerae O1 organisms can be biochemically typed into classical and El Tor biotypes. The O1 serogroup consists of Ogawa and Inaba serotypes, depending, respectively, on the presence or absence of a 2-O-methyl group in the nonreducing (upstream) terminal sugar of the O-specific polysaccharide (OSP) component of the lipopolysaccharide (LPS) (3, 4). Protection against cholera is serogroup specific, with serogroup specificity being determined by the OSP component of LPS (5-10). Previous infection with V. cholerae O1 provides no protection against cholera caused by V. cholerae O139 and vice versa (9,11,12). Ogawa and Inaba serotypes frequently fluctuate during cholera outbreaks, switching most commonly from Ogawa to Inaba (13). Immune responses against Inaba and Ogawa OSP cross-react, with higher immune responses targeting the homologous infecting serotype. Currently, a hybrid strain of V. cholerae O1 El Tor expressing classical cholera toxin (CT) predominates globally (14,15).Children under 5 years of age in regions where cholera is endemic have the highest burden of disease (16,17), although both children...

ABSTRACTCurrent oral cholera vaccines induce lower protective efficacy and shorter duration of protection against cholera than wild-type infection provides, and this difference is most pronounced in young children. Despite this, there are limited data comparing immune responses in children following wild-type disease versus vaccination, especially with regard to memory responses associated with long-term immunity. Here, we report a comparison of immune responses in young children (2 to 5 years of age;n= 20) and older children (6 to 17 years of age;n= 20) given two doses of an oral killed cholera vaccine containing recombinant cholera toxin B subunit (CtxB) 14 days apart and compare these responses to those induced in similarly aged children recovering from infection withVibrio choleraeO1 Ogawa in Bangladesh. We found that the two vaccine groups had comparable vibriocidal and lipopolysaccharide (LPS)-specific plasma antibody responses. Vaccinees developed lower levels of IgG memory B cell (MBC) responses against CtxB but no significant MBC responses against LPS. In contrast, children recovering from natural cholera infection developed prominent LPS IgG and IgA MBC responses, as well as CtxB IgG MBC responses. Plasma LPS IgG, IgA, and IgM responses, as well as vibriocidal responses, were also significantly higher in children following disease than after vaccination. Our findings suggest that acute and memory immune responses following oral cholera vaccination in children are significantly lower than those observed following wild-type disease, especially responses targeting LPS. These findings may explain, in part, the lower efficacy of oral cholera vaccination in children.