Antigen-Specific Memory B-Cell Responses to Vibrio cholerae O1 Infection in Bangladesh

Cholera, caused by Vibrio cholerae, is a noninvasive dehydrating enteric disease with a high mortality rate if untreated. Infection with V. cholerae elicits long-term protection against subsequent disease in countries where the disease is endemic. Although the mechanism of this protective immunity is unknown, it has been hypothesized that a protective mucosal response to V. cholerae infection may be mediated by anamnestic responses of memory B cells in the gut-associated lymphoid tissue. To characterize memory B-cell responses to cholera, we enrolled a cohort of 39 hospitalized patients with culture-confirmed cholera and evaluated their immunologic responses at frequent intervals over the subsequent 1 year. Memory B cells to cholera antigens, including lipopolysaccharide (LPS), and the protein antigens cholera toxin B subunit (CTB) and toxin-coregulated pilus major subunit A (TcpA) were enumerated using a method of polyclonal stimulation of peripheral blood mononuclear cells followed by a standard enzyme-linked immunospot procedure. All patients demonstrated CTB, TcpA, and LPS-specific immunoglobulin G (IgG)and IgA memory responses by day 90. In addition, these memory B-cell responses persisted up to 1 year, substantially longer than other traditional immunologic markers of infection with V. cholerae. While the magnitude of the LPS-specific IgG memory B-cell response waned at 1 year, CTB- and TcpA-specific IgG memory B cells remained significantly elevated at 1 year after infection, suggesting that T-cell help may result in a more durable memory B-cell response to V. cholerae protein antigens. Such memory B cells could mediate anamnestic responses on reexposure to V. cholerae.Vibrio cholerae, the etiologic agent of cholera, causes an estimated 3 to 5 million cases of secretory diarrhea, resulting in over 100,000 deaths annually (24). Strains of V. cholerae can be differentiated serologically by the O side chain of the lipopolysaccharide (LPS) component of the outer membrane. Although more than 200 different serogroups have been isolated from the environment, the vast majority of strains that produce cholera belong to serogroup O1 or O139, both of which consist of noninvasive pathogens that colonize the mucosal surface of the small intestine (19). V. cholerae O1 biotype El Tor is currently the predominant cause of cholera globally and in Bangladesh.The mechanisms of protective immunity to cholera are not known. Volunteer and epidemiologic studies demonstrate that clinically apparent infection with V. cholerae confers long-term protection of at least 3 years against subsequent disease (7, 12, 13). The best-studied marker of protective immunity is the vibriocidal antibody, a complement-dependent bactericidal antibody; however, there is no vibriocidal antibody titer at which complete protection is achieved (20). Furthermore, the vibriocidal response wanes rapidly, and it is hypothesized that the vibriocidal antibody may reflect other longer-lasting, protective immune responses occurring at the mucosal surface (3).Patients with cholera develop additional humoral immune responses to several antigens including cholera toxin subunit B (CTB), toxin-coregulated pilus major subunit A (TcpA), and LPS (1). We have recently shown that serum anti-CTB immunoglobulin A (IgA) antibody levels are also associated with protective immunity independent of the vibriocidal antibody on exposure to cholera, but serum IgA levels also wane rapidly after infection (10). Although levels of serum anti-LPS and anti-CTB IgG antibodies increase considerably after infection, these have not been shown to correlate with protection from V. cholerae infection in humans (8, 10).Cholera patients develop substantial mucosal immune responses after infection. These can be measured by the transient increase of antigen-specific IgA antibody-secreting cells (ASC) in the circulation. The ASC assay quantifies lymphocytes that are activated in the gut-associated lymphoid tissue (GALT) when they transiently circulate in blood before rehoming to mucosal effector sites (6, 16, 17). These predominantly gut-homing ASC peak in the circulation between 5 and 10 days after onset of illness but are no longer detected during late convalescence as they return to populate the GALT (1, 11). Because V. cholerae is a noninvasive pathogen, it is hypothesized that protective immunity is derived from the activity of the secretory IgA system of the GALT (14, 22, 23). Volunteer studies of subjects receiving CTB orally demonstrate local and systemic generation of anti-CTB IgA antibodies that peak at 7 days following ingestion but decline to baseline by 15 months; however, these volunteers mount anamnestic responses with a rapid return to peak mucosal antibody titers in as few as 3 days after subsequent challenge with oral CTB (22, 23). It is thus hypothesized that protection from cholera may be mediated by rapid anamnestic responses of memory B cells in the GALT to V. cholerae antigens.In this study, we examined the memory B-cell immune responses to V. cholerae infection, using a polyclonal stimulation method to enhance the detection of memory B cells in the circulation by inducing their proliferation and differentiation into antibody-secreting plasmablasts (4, 5). A standardized two-color enzyme-linked immunospot (ELISPOT) assay allows for the quantification of small numbers of circulating V. cholerae antigen-specific memory B cells as a proportion of total memory B cells (2, 4, 5, 21). Using this system, we have previously shown that cholera patients develop CTB-specific IgG memory B-cell responses that persist for at least 3 months after infection (11). The present study further characterizes memory B-cell responses to CTB, TcpA, and LPS for both IgA and IgG isotypes for a period of 1 year following acute infection and examines differences between the memory B-cell responses to the T-cell-dependent protein antigens CTB and TcpA and the T-cell-independent antigen LPS.     

Antibody-Secreting Cell Responses after Vibrio cholerae O1 Infection and Oral Cholera Vaccination in Adults in Bangladesh

Infection with Vibrio cholerae and oral cholera vaccines (OCVs) induce transient circulating plasmablast responses that peak within approximately 7 days after infection or vaccination. We previously demonstrated that plasmablast responses strongly correlate with subsequent levels of V. cholerae-specific duodenal antibodies up to 6 months after V. cholerae infection. Hence, plasmablast responses provide an early window into the immunologic memory at the mucosal surface. In this study, we characterized plasmablast responses following V. cholerae infection using a flow cytometrically defined population and compared V. cholerae-specific responses in adult patients with V. cholerae O1 infection and vaccinees who received the OCV Dukoral (Crucell Vaccines Canada). Among flow cytometrically sorted populations of gut-homing plasmablasts, almost 50% of the cells recognized either cholera toxin B subunit (CtxB) or V. cholerae O1 lipopolysaccharide (LPS). Using a traditional enzyme-linked immunosorbent spot assay (ELISPOT), we found that infection with V. cholerae O1 and OCVs induce similar responses to the protein antigen CtxB, but responses to LPS were diminished after OCV compared to those after natural V. cholerae infection. A second dose of OCV on day 14 failed to boost circulating V. cholerae-specific plasmablast responses in Bangladeshi adults. Our results differ from those in studies from areas where cholera is not endemic, in which a second vaccination on day 14 significantly boosts plasmablast responses. Given these results, it is likely that the optimal boosting strategies for OCVs differ significantly between areas where V. cholerae infection is endemic and those where it is not.     

Increased Levels of Inflammatory Mediators in Children and Adults Infected with Vibrio cholerae O1 and O139

Investigations were carried out to study the production of factors associated with the innate immune response in the systemic and mucosal compartments in adults and children infected with Vibrio cholerae O1 and V. cholerae O139. The levels of nonspecific mediators of the innate defense system, i.e., prostaglandin E₂ (PGE₂), leukotriene B₄ (LTB₄), and lactoferrin (Lf), as well as myeloperoxidase (MPO), were elevated at the acute stage of the disease in stools obtained from both O1- and O139-infected adults and children. In the systemic compartment, the levels of Lf were increased after onset of disease, which in children remained elevated up to convalescence compared to the healthy controls. Increased concentrations of C-reactive protein were seen in the sera of adult cholera patients at the acute stage of infection. Elevated levels of the nitric oxide (NO^·) metabolites (nitrite and nitrate [NO₂⁻ and NO₃⁻]) were detected in plasma but not in urine. The activity of the scavenger of reactive oxygen species, superoxide dismutase, was higher in the plasma of adults immediately after the onset of disease, suggesting that an active scavenging of reactive oxygen species was taking place. The concentration of 8-iso-prostaglandin F_2α remained unchanged in the systemic and mucosal compartments in the study subjects. After the recovery of patients from cholera, the concentration of the majority of the metabolites decreased to baseline levels by day 30 after the onset of infection. Immunohistochemical staining showed increased tissue expression of MPO, Lf, and inducible nitric oxide synthase at the acute stage in the duodenal biopsies of adults and rectal biopsies obtained from children with cholera. Very little difference was seen in the levels of the different inflammatory mediators in patients infected with V. cholerae O1 or the encapsulated V. cholerae O139. In summary, these results suggest that elevated concentrations of Lf, MPO, PGE₂, LTB₄, and NO^·, as well as other metabolites, during the acute stage of the disease indicate that the innate defense system, as well as the inflammatory process, is activated in both adults and pediatric patients infected with V. cholerae O1 and O139.     

Memory T-Cell Responses to Vibrio cholerae O1 Infection

Vibrio cholerae O1 can cause diarrheal disease that may be life-threatening without treatment. Natural infection results in long-lasting protective immunity, but the role of T cells in this immune response has not been well characterized. In contrast, robust B-cell responses to V. cholerae infection have been observed. In particular, memory B-cell responses to T-cell-dependent antigens persist for at least 1 year, whereas responses to lipopolysaccharide, a T-cell-independent antigen, wane more rapidly after infection. We hypothesize that protective immunity is mediated by anamnestic responses of memory B cells in the gut-associated lymphoid tissue, and T-cell responses may be required to generate and maintain durable memory B-cell responses. In this study, we examined B- and T-cell responses in patients with severe V. cholerae infection. Using the flow cytometric assay of the specific cell-mediated immune response in activated whole blood, we measured antigen-specific T-cell responses using V. cholerae antigens, including the toxin-coregulated pilus (TcpA), a V. cholerae membrane preparation, and the V. cholerae cytolysin/hemolysin (VCC) protein. Our results show that memory T-cell responses develop by day 7 after infection, a time prior to and concurrent with the development of B-cell responses. This suggests that T-cell responses to V. cholerae antigens may be important for the generation and stability of memory B-cell responses. The T-cell proliferative response to VCC was of a higher magnitude than responses observed to other V. cholerae antigens.Vibrio cholerae is a gram-negative bacterium that can cause a severe, acute secretory diarrhea. Serological differentiation of V. cholerae strains is based on the O-side chain of the lipopolysaccharide (LPS) component of the outer membrane. Of the more than 200 serogroups of V. cholerae identified, only the O1 and O139 serogroups can cause epidemic cholera (44). These pathogens are noninvasive and colonize the mucosal surface of the small intestine (44).Natural infection with V. cholerae is known to provide protection against subsequent disease, but the mechanism of this protective immunity is not fully characterized. The vibriocidal antibody is a complement-dependent bactericidal antibody that is associated with protection from infection. However, no known threshold level of the vibriocidal antibody confers complete protection from V. cholerae infection, and some individuals with low serum vibriocidal antibody titers are still protected. This suggests that the vibriocidal titer may be a surrogate marker (16, 45). Elevated serum immunoglobulin A (IgA) antibody levels specific for the B subunit of cholera toxin (CTB), the major structural subunit of a type IV pilus (TcpA), and LPS are also associated with protective immunity in areas where cholera is endemic (19). However, after natural infection, the serum levels of these antibodies wane more rapidly than protective immunity (19). Patients with cholera develop memory B-cell responses of both the IgG and the IgA isotype to at least two V. cholerae protein antigens, CTB and TcpA. These responses are detectable for at least 1 year after infection and persist even after V. cholerae antigen-specific antibody-secreting cells and serum antibody titers have returned to baseline (18). B-cell memory responses also develop for the T-cell independent antigen LPS, but these responses wane more rapidly than memory B-cell responses to protein antigens, suggesting that durable memory B-cell responses to some V. cholerae antigens may be T-cell dependent (18).We have recently demonstrated that cholera patients mount a primed T-cell response in the mucosa after V. cholerae O1 infection (6). We hypothesize that protection from cholera may be mediated by memory B cells capable of an anamnestic response in the gut mucosa and that these memory B cells may depend on stimulation provided by memory T cells for their development and maintenance. T cells may contribute to the activation of B cells during V. cholerae infection by secreting stimulatory cytokines and direct contact with B cells in lymph nodes. Therefore, T cells may have an important role in protective immunity to V. cholerae infection.We characterized the memory T-cell responses to V. cholerae antigens following natural V. cholerae infection and compared these with serological responses to the same antigens. Previously, our group has studied various V. cholerae antigens, including mannose-sensitive hemagglutinin, TcpA, CTB, and LPS (22, 33, 37). We also included in the present study responses to a novel antigen, V. cholerae cytolysin/hemolysin (VCC) (31, 32). The hly gene that encodes the VCC protein is widespread across both pathogenic and environmental strains of V. cholerae, suggesting that VCC may impart an advantage to the organism (42). Although the precise role of VCC in V. cholerae infection is unknown, VCC is the primary virulence factor in V. cholerae infection with non-O1, non-O139 strains that do not produce cholera toxin (12, 46). The immune response to VCC is not well understood; however, recent studies suggest that VCC may promote a Th2 response in V. cholerae infection (2). In addition, the cytolytic activity of VCC may generate epithelial destruction that allows other V. cholerae antigens to penetrate the mucosa and promote the inflammatory response observed in V. cholerae infection (35, 39).     

Memory B Cell Responses to Vibrio cholerae O1 Lipopolysaccharide Are Associated with Protection against Infection from Household Contacts of Patients with Cholera in Bangladesh

Vibrio cholerae O1 causes cholera, a dehydrating diarrheal disease. We have previously shown that V. 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 circulating V. cholerae O1 antigen-specific memory B cells on enrollment was associated with protection against V. cholerae infection 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 with V. cholerae O1.     

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

Immunity against Vibrio cholerae O1 is serogroup specific, and serogrouping is defined by the O-specific polysaccharide (OSP) part of lipopolysaccharide (LPS). Despite this, human immune responses to V. cholerae OSP have not previously been characterized. We assessed immune responses against V. cholerae OSP in adults with cholera caused by V. cholerae O1 El Tor serotype Inaba or Ogawa in Dhaka, Bangladesh, using O1 OSP-core–bovine serum albumin (OSPc:BSA) conjugates; responses targeted OSP in these conjugates. Responses of Inaba-infected patients to Inaba OSP and LPS increased significantly in IgG, IgM, and IgA isotypes from the acute to convalescent phases of illness, and the responses correlated well between OSP and LPS (R = 0.86, 0.73, and 0.91, respectively; P < 0.01). Plasma IgG, IgM, and IgA responses to Ogawa OSP and LPS in Ogawa-infected patients also correlated well with each other (R = 0.60, 0.60, and 0.92, respectively; P < 0.01). Plasma IgM responses to Inaba OSP and Ogawa OSP correlated with the respective serogroup-specific vibriocidal antibodies (R = 0.80 and 0.66, respectively; P < 0.001). Addition of either OSPc:BSA or LPS, but not BSA, to vibriocidal assays inhibited vibriocidal responses in a comparable and concentration-dependent manner. Mucosal IgA immune responses to OSP and LPS were also similar. Our study is the first to characterize anti-OSP immune responses in patients with cholera and suggests that responses targeting V. cholerae LPS, including vibriocidal responses that correlate with protection against cholera, predominantly target OSP. Induction of anti-OSP responses may be associated with protection against cholera, and our results may support the development of a vaccine targeting V. cholerae OSP.     

Haitian variant Vibrio cholerae O1 Ogawa caused cholera outbreaks in Odisha

PurposeDiarrheal disorders particularly cholera cause a significant threat resulting in high morbidity and mortality in the coastal and tribal areas of Odisha. Two sequential diarrheal outbreaks reported in 2016 from Balasore and Rayagada districts of Odisha were investigated to find out the causative organisms, antibiogram profile and molecular analysis of the isolated pathogens.MethodBacteriological analysis and antibiogram profiles of the pathogens were carried out as per the standard procedure followed. The double mismatch amplification mutation (DMAMA) PCR for ctxB gene, sequencing and pulse-field gel electrophoresis (PFGE) were carried out on Vibrio cholerae O1 strains.ResultsThe rectal swabs and water samples from these districts were positive for V. cholerae O1 Ogawa biotype El Tor. The V. cholerae O1 strains isolated from Balasore district were multidrug resistant to many antibiotics which differed from the isolates of Rayagada district. The DMAMA PCR assay on all clinical and water isolates from these areas and some strains from other districts exhibited ctxB7 allele of V. cholerae O1 which correlates with the sequencing results having different pulsotypes. The Haitian variant of V. cholerae O1 strains which were compared with the V. cholerae O1 strains of 1999 and 2000 exhibited different pulsotypes.ConclusionThe present study reports cholera outbreaks due to multidrug resistant ctxB7 allele of V. cholerae O1 from both coastal (Balasore) and tribal (Rayagada) areas of Odisha.     

O1群小川型霍乱弧菌单克隆抗体的制备与鉴定

目的制备抗O1群小川型霍乱弧菌(VibriocholeraeO1serotypeOgawa)特异性单克隆抗体(McAb),为霍乱的早期快速诊断提供有力的抗体工具。方法以灭活的O1群小川型霍乱弧菌免疫Balbc小鼠,通过杂交瘤技术制备针对O1群小川型霍乱弧菌的McAb,以间接ELISA法对所需的杂交瘤细胞株进行筛选,分析其亚类,检测其效价及相对亲和力,以间接ELISA和Westernblot鉴定McAb特异性,并进行McAb结合表位分析。结果融合了602株能分泌抗O1群小川型霍乱弧菌McAb的杂交瘤细胞株,最后得到5株能稳定分泌特异性的针对该McAb的细胞株,其抗体亚类分别为3株IgG1,1株IgG2b,1株IgG3;腹水效价均达1×10-6;亲和常数在1×108～1×109之间。间接ELISA法及Westernblot证实所获的McAb可与O1群小川型霍乱弧菌发生特异性反应。ELISA相加实验结果显示除有2株McAb识别相同的抗原表位外,其余均识别不同的抗原表位。结论获得霍乱弧菌O1群小川型特异性McAb,为O1群小川型霍乱早期快速诊断和发病机理的研究提供基础。     

Comparison of memory B cell, antibody-secreting cell, and plasma antibody responses in young children, older children, and adults with infection caused by Vibrio cholerae O1 El Tor Ogawa in Bangladesh

Children bear a large component of the global burden of cholera. Despite this, little is known about immune responses to cholera in children, especially those under 5 years of age. Cholera vaccine studies have demonstrated lower long-term protective efficacy in young children than in older children and adults. Memory B cell (MBC) responses may correlate with duration of protection following infection and vaccination. Here we report a comparison of immune responses in young children (3 to 5 years of age; n = 17), older children (6 to 17 years of age; n = 17), and adults (18 to 60 years of age; n = 68) hospitalized with cholera in Dhaka, Bangladesh. We found that young children had lower baseline vibriocidal antibody titers and higher fold increases in titer between day 2 and day 7 than adults. Young children had higher baseline IgG plasma antibody levels to Vibrio cholerae antigens, although the magnitudes of responses at days 7 and 30 were similar across age groups. As a surrogate marker for mucosal immune responses, we assessed day 7 antibody-secreting cell (ASC) responses. These were comparable across age groups, although there was a trend for older age groups to have higher levels of lipopolysaccharide-specific IgA ASC responses. All age groups developed comparable MBC responses to V. cholerae lipopolysaccharide and cholera toxin B subunit at day 30. These findings suggest that young children are able to mount robust vibriocidal, plasma antibody, ASC, and MBC responses against V. cholerae O1, suggesting that under an optimal vaccination strategy, young children could achieve protective efficacy comparable to that induced in adults.     

Development of Immunoglobulin M Memory to Both a T-Cell-Independent and a T-Cell-Dependent Antigen following Infection with Vibrio cholerae O1 in Bangladesh

Vibrio cholerae O1 can cause severe watery diarrhea that can be life-threatening without treatment. Infection results in long-lasting protection against subsequent disease. Development of memory B cells of the immunoglobulin G (IgG) and IgA isotypes to V. cholerae O1 antigens, including serotype-specific lipopolysaccharide (LPS) and the B subunit of cholera toxin (CTB), after cholera infection has been demonstrated. Memory B cells of the IgM isotype may play a role in long-term protection, particularly against T-cell-independent antigens, but IgM memory has not been studied in V. cholerae O1 infection. Therefore, we assayed acute- and convalescent-phase blood samples from cholera patients for the presence of memory B cells that produce cholera antigen-specific IgM antibody upon polyclonal stimulation in in vitro culture. We also examined the development of serological and antibody-secreting cell responses following infection. Subjects developed significant IgM memory responses by day 30 after infection, both to the T-cell-independent antigen LPS and to the T-cell-dependent antigen CTB. No significant corresponding elevations in plasma IgM antibodies or circulating IgM antibody-secreting cells to CTB were detected. In 17 subjects followed to day 90 after infection, significant persistence of elevated IgM memory responses was not observed. The IgM memory response to CTB was negatively correlated with the IgG plasma antibody response to CTB, and there was a trend toward negative correlation between the IgM memory and IgA plasma antibody responses to LPS. We did not observe an association between the IgM memory response to LPS and the vibriocidal titer.Vibrio cholerae continues to be a significant global health burden as a cause of severe secretory diarrhea, resulting in an estimated three to five million annual cases, with more than 100,000 deaths from rapid dehydration (47); cholera has recently become endemic in new regions (44, 45). V. cholerae is a noninvasive pathogen that colonizes the mucosal surface of the small intestine. Strains can be distinguished serologically by the O antigen of the lipopolysaccharide (LPS); V. cholerae O1 is the most common cause of cholera in South Asia as well as globally. The O1 serogroup has two major biotypes, El Tor and classical, and two major serotypes, Inaba and Ogawa (35). Natural infection with V. cholerae O1 El Tor induces protective immunity that lasts for at least 3 to 10 years in both areas where cholera is not endemic and areas where it is endemic (21). It remains unknown, however, what aspects of the adaptive immune response to cholera confer this long-term protection.V. cholerae-infected patients mount immunologic responses to both protein and polysaccharide antigens, including rises in both serum immunoglobulin G (IgG) and IgA antibodies (14). A number of these serological responses have been shown to correlate with protection against reinfection; these include the complement-dependent serum vibriocidal antibody (14) and IgA (but not IgG) responses to LPS, cholera toxin B subunit (CTB), and toxin coregulated pilus A (TcpA) (17). These serological responses, however, are short-lived (4, 32), and the association of the vibriocidal titer with protection is not absolute (36), suggesting that these responses may reflect protection from more recent exposure but that other immunologic mechanisms mediate longer-term protection. In addition to serological responses, development of mucosal immune responses to intestinal antigens can be detected in the blood, when B cells activated by antigen in the gut-associated lymphoid tissues circulate transiently in the blood as antibody-secreting cells (ASCs), before homing back to intestinal mucosal surfaces (11, 26). Circulation of ASCs specific to both LPS and CTB is seen after cholera infection, peaking around the seventh day after infection and declining by day 11 (32).Responses of the IgM isotype to cholera antigens have been less thoroughly investigated than the IgG and IgA responses. However, IgM defenses may be an important component of the overall immunologic response to cholera, since vibriocidal antibodies are principally of the IgM isotype (22) and IgM levels of pooled convalescent-phase serum samples correspond closely with vibriocidal activity (24), which in turn correlates with immunity (14). The pentameric structure of IgM facilitates strong cross-linking of antigens and activation of complement in the defense against other gram-negative enteric bacteria (2).We have recently shown development of memory B cells of both the IgG and IgA isotypes to LPS, CTB, and TcpA; these cells persisted in the circulation beyond 1 year for the protein antigens CTB and TcpA, but were not measurably above baseline levels by 9 to 12 months after infection for the polysaccharide-containing antigen LPS (16, 18). These circulating memory B cells can be detected by ex vivo polyclonal stimulation of peripheral blood mononuclear cells (PBMCs); stimulated memory B cells mature into ASCs detectable by enzyme-linked immunospot (ELISPOT) assay. Alternatively, memory B-cell responses can be detected by measuring antigen-specific antibodies secreted by maturing ASCs during the ex vivo stimulation of PBMCs in the memory B-cell assay (18).Memory B cells relevant for cholera immunity may include IgM⁺ as well as switched-memory (IgA⁺ and IgG⁺) populations. The majority of circulating IgM⁺ cells are naïve B cells, but some IgM⁺ cells bear the memory cell marker CD27⁺, and recent evidence suggests that these IgM⁺CD27⁺ cells are true memory B cells whose immunoglobulin variable region genes have undergone somatic hypermutation in response to antigen in early-stage germinal centers (39). IgM⁺ memory cells can undergo isotype switching to produce IgG, IgA, or IgE antibody, but they also have a role in producing rapid, high-affinity IgM antibody responses to acute infection (19, 37, 46). In this study, we have measured the development of memory B-cell responses of the IgA, IgG, and IgM isotypes to both a protein (CTB) and a nonprotein (LPS) antigen, and we compared these memory responses with other immunologic responses in patients after V. cholerae infection in Bangladesh.     

Transcutaneous Immunization with a Vibrio cholerae O1 Ogawa Synthetic Hexasaccharide Conjugate following Oral Whole-Cell Cholera Vaccination Boosts Vibriocidal Responses and Induces Protective Immunity in Mice

A shortcoming of currently available oral cholera vaccines is their induction of relatively short-term protection against cholera compared to that afforded by wild-type disease. We were interested in whether transcutaneous or subcutaneous boosting using a neoglycoconjugate vaccine made from a synthetic terminal hexasaccharide of the O-specific polysaccharide of Vibrio cholerae O1 (Ogawa) coupled to bovine serum albumin as a carrier (CHO-BSA) could boost lipopolysaccharide (LPS)-specific and vibriocidal antibody responses and result in protective immunity following oral priming immunization with whole-cell cholera vaccine. We found that boosting with CHO-BSA with immunoadjuvantative cholera toxin (CT) or Escherichia coli heat-labile toxin (LT) following oral priming with attenuated V. cholerae O1 vaccine strain O395-NT resulted in significant increases in serum anti-V. cholerae LPS IgG, IgM, and IgA (P < 0.01) responses as well as in anti-Ogawa (P < 0.01) and anti-Inaba (P < 0.05) vibriocidal titers in mice. The LPS-specific IgA responses in stool were induced by transcutaneous (P < 0.01) but not subcutaneous immunization. Immune responses following use of CT or LT as an adjuvant were comparable. In a neonatal mouse challenge assay, immune serum from boosted mice was associated with 79% protective efficacy against death. Our results suggest that transcutaneous and subcutaneous boosting with a neoglycoconjugate following oral cholera vaccination may be an effective strategy to prolong protective immune responses against V. cholerae.     

Cholera due to altered El Tor strains of Vibrio cholerae O1 in Bangladesh

We determined the types of cholera toxin (CT) produced by a collection of 185 Vibrio cholerae O1 strains isolated in Bangladesh over the past 45 years. All of the El Tor strains of V. cholerae O1 isolated since 2001 produced CT of the classical biotype, while those isolated before 2001 produced CT of the El Tor biotype.     

Emergence of Vibrio cholerae O1 biotype El Tor serotype Inaba from the prevailing O1 Ogawa serotype strains in India

The toxigenic Inaba serotype of Vibrio cholerae O1 biotype El Tor reappeared in India in 1998 and 1999, almost 10 years after its last dominance in Calcutta in 1989. Extensive molecular characterization by ribotyping, restriction fragment length polymorphism, and pulsed-field gel electrophoresis indicated that recent Inaba strains are remarkably different from the earlier Inaba strains but are very similar to the prevailing V. cholerae O1 Ogawa El Tor biotype strains. The antibiograms of the Inaba strains were also similar to those of the recent V. cholerae Ogawa strains. These V. cholerae O1 Inaba strains appear to have evolved from the currently prevailing Ogawa strains and are likely to dominate in the coming years.     

Cholera Caused by Vibrio cholerae O1 Induces T-Cell Responses in the Circulation

Considerable effort is being made to understand the acute and memory antibody responses in natural cholera infection, while rather less is known about the roles of cellular immune responses involving T and B lymphocytes. We studied responses in adult patients hospitalized with cholera caused by Vibrio cholerae O1. Peripheral blood mononuclear cells from patients (n = 15) were analyzed by flow cytometry after stimulation with V. cholerae O1 membrane protein (MP) or toxin-coregulated pilus antigen (TcpA). The gamma interferon (IFN-γ) and interleukin-13 (IL-13) responses in stimulated-lymphocyte supernatants were studied. The responses were compared with those of healthy controls (n = 10). Patients responded with increased frequencies of gut-homing CD4⁺ T cells (CD4⁺ β7⁺), gut-homing CD8⁺ T cells (CD8⁺ β7⁺), and gut-homing B cells (CD19⁺ β7⁺) at the early and/or late convalescent stages compared to the acute stage. After stimulation with MP or TcpA, proliferation of CD4⁺ and CD8⁺ T cells was increased at the acute stage and/or early convalescent stage compared to healthy controls. Increased IL-13 and IFN-γ responses were observed after antigenic stimulation at the acute and convalescent stages compared to healthy controls. Thus, increases in the levels of gut-homing T and B cells, as well as involvement of CD8 and CD4 Th1-mediated (IFN-γ) and CD4 Th2-mediated (IL-13) cytokine responses, take place in acute dehydrating disease caused by V. cholerae O1. Further studies are needed to determine if such responses are also stimulated after immunization with oral cholera vaccines and if these responses play a role in protection following exposure to cholera.Vibrio cholerae O1 is a common causative agent of acute watery diarrhea in children and adults in the developing world (1, 3, 10, 19). After colonizing the proximal small intestine, this bacterium produces cholera toxin, which induces a profuse secretory diarrhea. Cholera remains a key public health problem that results in epidemics in resource-poor settings.It is believed that the immune response to cholera is initiated by antigen presentation in the Peyer''s patches of the gastrointestinal mucosa, followed by migration of the stimulated antigen-specific B cells to regional lymph nodes and differentiation of these cells into specific antibody-secreting cells (28). Stimulation of the common mucosal immune system leads to production of both local and systemic antibodies (2, 15, 27) to virulence antigens of V. cholerae (25, 28).Natural cholera infection is believed to give rise to long-term protection against subsequent disease. Robust systemic and mucosal antibodies are produced to the V. cholerae lipopolysaccharide, to cholera toxin, and to colonization factors, including the major subunit of the toxin-coregulated pilus, TcpA (2, 24, 25, 28). We have recently shown that there is induction of memory B-cell responses following infection, which may play a role in longer-lasting protection (14). In addition, recent evidence suggests that an innate component of the immune system may also play a role in the host response to cholera (9, 22, 26). Studies with experimental animals have shown that the mucosal immune response to cholera toxin is T cell dependent and that CD4 T helper cells have an important role (7, 12, 13). However, not much is known about the role of the adaptive cellular immune responses in patients with cholera. The aim of the present study was to decipher the role of T- and B-cell-mediated immune responses in natural cholera infection in adults hospitalized with dehydrating illness, who were followed from the acute stage to convalescence.     

霍乱弧菌O1群稻叶型流行株和非流行株的蛋白质谱特征分析

目的探讨霍乱弧菌01群稻叶型流行株和非流行株的蛋白表达的差异。方法利用裂解液处理霍乱弧菌,提取全菌蛋白;采用pH梯度等电聚焦对菌蛋白进行双向电泳;考马斯亮蓝染色后获得的双向电泳图谱,并利用ImageMaster2DElite5．0图象分析软件进行分析,找出差异蛋白;在此基础上,胰蛋白酶消化这些特殊差异蛋白,并进行质谱（MALDI-TOF—MS）分析。结果获得了（1081±16）个蛋白斑点,蛋白主要集中在pI4．00—7．20之间,重复胶的匹配点数为（1057±28）,匹配率为97．85％;发现了有明显差异的21个蛋白点,并进行了质谱鉴定。结论获得了霍乱弧菌01群稻叶型流行株和非流行株的差异表达蛋白。     

Laboratory-acquired Vibrio cholerae O1 infection in Austria, 2008

Vibrio cholerae infection is a rare but well-documented cause of laboratory-associated illness. We report on the first case of indigenous cholera documented in Austria after more than fifty years. In April 2008, the National Reference Centre for V. cholerae received an isolate of V. cholerae O1, serotype Ogawa, cultured from the stool specimen of a patient consulting a general practitioner because of watery diarrhea. The 23 year old microbiology student had been working with viable V. cholerae for 4 weeks in a practical laboratory course. Two days before onset of symptoms an open 300 mL Erlenmeyer flask with approx. 30 mL of overnight V. cholerae culture tipped over and spilled into a laboratory shaker near the student's working place. Wearing gloves and protective gowns, the student and her supervisor immediately cleaned and decontaminated the shaker. As a consequence of this laboratory incident, the institution in question replaced the clamp-less shaker plate by a traditional shaker plate with mechanical clamps.     

Comparative study of Vibrio cholerae non-O1 protease and soluble hemagglutinin with those of Vibrio cholerae O1.

Protease and soluble hemagglutinating activities produced by a non-O1 Vibrio cholerae strain isolated from a patient with diarrhea were compared with similar activities produced by V. cholerae O1. The soluble protease activities were indistinguishable in heat stability, immunodiffusion, inhibition by antiserum, and electrophoretic analysis. On the other hand, the soluble hemagglutinating activities of both strains were not completely identical. The hemagglutinating activity of the non-O1 V. cholerae strain was not inhibited by Zincov; it was more sensitive to inhibition by normal serum, and it had an unusual pattern of heat stability. Heating at 100 degrees C resulted in some recovery of activity of a sample previously inactivated by heating at 60 degrees C.     

Genetic diversity of El Tor strains of Vibrio cholerae O1 with hybrid traits isolated from Bangladesh and Mozambique

Vibrio cholerae O1 strains that are hybrids between the classical and El Tor biotypes were isolated during two consecutive years (2004-2005) from diarrheal patients in Mozambique. Similar variants isolated in Bangladesh and recently isolated El Tor strains were analyzed for genetic diversity. Pulsed-field gel electrophoresis (PFGE) analysis using the restriction enzyme NotI, resulted in 18-21 bands showed five closely related PFGE patterns that were distributed similarly in both years (2004-2005) among the 80 strains tested in Mozambique. Overall based on the PFGE patterns the hybrids indicated an El Tor lineage. The restriction patterns of whole-chromosomal DNA grouped the hybrid strains from Mozambique into a separate cluster from Bangladeshi clinical and environmental hybrid strains. A high molecular weight band of 398kb that contain rstR allele of the classical type was detected from all hybrid strains, which was absent in all conventional classical and El Tor strains. This band could be designated as a marker for the hybrid strains. This study suggests that hybrid strains from Mozambique are closely related to each other, different from Bangladeshi hybrid strains that are diverse in nature and all hybrid strains differed markedly from conventional classical and El Tor strains.     

Emergence of a new clone of toxigenic Vibrio cholerae O1 biotype El Tor displacing V. cholerae O139 Bengal in Bangladesh.

The emergence of Vibrio cholerae O139 Bengal in 1993, its rapid spread in an epidemic form, in which it replaced existing strains of V. cholerae O1 during 1992 and 1993, and the subsequent reemergence of V. cholerae O1 of the El Tor biotype in Bangladesh since 1994 have raised questions regarding the origin of the reemerged El Tor vibrios. We studied 50 El Tor vibrio strains isolated in Bangladesh and four other countries in Asia and Africa before the emergence of V. cholerae O139 and 32 strains isolated in Bangladesh during and after the epidemic caused by V. cholerae O139 and 32 strains isolated in Bangladesh during and after the epidemic caused by V. cholerae O139 to determine whether the reemerged El Tor vibrios were genetically different from the El Tor vibrios which existed before the emergence of V. cholerae O139. Analysis of restriction fragment length polymorphisms in genes for conserved rRNA, cholera toxin (ctxA), and zonula occludens toxin (zot) or in DNA sequences flanking the genes showed that the El Tor strains isolated before the emergence of V. cholerae O139 belonged to four different ribotypes and four different ctx genotypes. Of 32 El Tor strains isolated after the emergence of O139 vibrios, 30 strains (93.7%) including all the clinical isolates belonged to a single new ribotype and a distinctly different ctx genotype. These results provide evidence that the reemerged El Tor strains represent a new clone of El Tor vibrios distinctly different from the earlier clones of El Tor vibrios which were replaced by the O139 vibrios. Further analysis showed that all the strains carried the structural and regulatory genes for toxin-coregulated pilus (tcpA, tcpI, and toxR). All strains of the new clone produced cholera toxin (CT) in vitro, as assayed by the GM1-dependent enzyme-linked immunosorbent assay, and the level of CT production was comparable to that of previous epidemic isolates of El Tor vibrios. Further studies are required to assess the epidemic potential of the newly emerged clone of V. cholerae O1 and to understand the mechanism of emergence of new clones of toxigenic V. cholerae.