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

Variants rs3804099 and rs3804100 in the TLR2 Gene Induce Different Profiles of TLR-2 Expression and Cytokines in Response to Spike of SARS-CoV-2

The present study aimed to identify in patients with severe COVID-19 and acute respiratory distress syndrome (ARDS) the association between rs3804099 and rs3804100 (TLR2) and evaluate the expression of TLR-2 on the cell surface of innate and adaptive cells of patients' carriers of C allele in at least one genetic variant. We genotyped 1018 patients with COVID-19 and ARDS. According to genotype, a subgroup of 12 patients was selected to stimulate peripheral blood mononuclear cells (PBMCs) with spike and LPS + spike. We evaluated soluble molecules in cell culture supernatants. The C allele in TLR2 (rs3804099, rs3804100) is not associated with a risk of severe COVID-19; however, the presence of the C allele (rs3804099 or rs3804100) affects the TLR-2 ability to respond to a spike of SARS-CoV-2 correctly. The reference group (genotype TT) downregulated the frequency of non-switched TLR-2+ B cells in response to spike stimulus; however, the allele's C carriers group is unable to induce this regulation, but they produce high levels of IL-10, IL-6, and TNF-α by an independent pathway of TLR-2. Findings showed that TT genotypes (rs3804099 and rs3804100) affect the non-switched TLR-2+ B cell distribution. Genotype TT (rs3804099 and rs3804100) affects the TLR-2's ability to respond to a spike of SARS-CoV-2. However, the C allele had increased IL-10, IL-6, and TNF-α by stimulation with spike and LPS.

Advances in phage display based nano immunosensors for cholera toxin

Cholera, a persistent global public health concern, continues to cause outbreaks in approximately 30 countries and territories this year. The imperative to safeguard water sources and food from Vibrio cholerae, the causative pathogen, remains urgent. The bacterium is mainly disseminated via ingestion of contaminated water or food. Despite the plate method's gold standard status for detection, its time-consuming nature, taking several days to provide results, remains a challenge. The emergence of novel virulence serotypes raises public health concerns, potentially compromising existing detection methods. Hence, exploiting Vibrio cholerae toxin testing holds promise due to its inherent stability. Immunobiosensors, leveraging antibody specificity and sensitivity, present formidable tools for detecting diverse small molecules, encompassing drugs, hormones, toxins, and environmental pollutants. This review explores cholera toxin detection, highlighting phage display-based nano immunosensors' potential. Engineered bacteriophages exhibit exceptional cholera toxin affinity, through specific antibody fragments or mimotopes, enabling precise quantification. This innovative approach promises to reshape cholera toxin detection, offering an alternative to animal-derived methods. Harnessing engineered bacteriophages aligns with ethical detection and emphasizes sensitivity and accuracy, a pivotal stride in the evolution of detection strategies. This review primarily introduces recent advancements in phage display-based nano immunosensors for cholera toxin, encompassing technical aspects, current challenges, and future prospects.

Long-Term Kinetics of Serological Antibodies against Vibrio cholerae Following a Clinical Cholera Case: A Systematic Review and Meta-Analysis

BACKGROUND

Approximately 2.9 million people worldwide suffer from cholera each year, many of whom are destitute. However, understanding of immunity against cholera is still limited. Several studies have reported the duration of antibodies following cholera; however, systematic reviews including a quantitative synthesis are lacking.

OBJECTIVE

To meta-analyze cohort studies that have evaluated vibriocidal, cholera toxin B subunit (CTB), and lipopolysaccharide (LPS) antibody levels following a clinical cholera case.

METHODS

Design: Systematic review and meta-analysis. We searched PubMed and Web of science for studies assessing antibodies against Vibrio cholerae in cohorts of patients with clinical cholera. Two authors independently extracted data and assessed the quality of included studies. Random effects models were used to pool antibody titers in adults and older children (aged ≥ 6 years). In sensitivity analysis, studies reporting data on young children (2-5 years) were included.

RESULTS

Nine studies met our inclusion criteria for systematic review and seven for meta-analysis. The pooled mean of vibriocidal antibody titers in adults and older children (aged ≥ 6 years) was 123 on day 2 post-symptom onset, which sharply increased on day 7 (pooled mean = 6956) and gradually waned to 2247 on day 30, 578 on day 90, and 177 on day 360. Anti-CTB IgA antibodies also peaked on day 7 (pooled mean = 49), followed by a rapid decrease on day 30 (pooled mean = 21), and further declined on day 90 (pooled mean = 10), after which it plateaued from day 180 (pooled mean = 8) to 360 (pooled mean = 6). Similarly, anti-CTB IgG antibodies peaked in early convalescence between days 7 (pooled mean = 65) and 30 (pooled mean = 69), then gradually waned on days 90 (pooled mean = 42) and 180 (pooled mean = 30) and returned to baseline on day 360 (pooled mean = 24). Anti-LPS IgA antibodies peaked on day 7 (pooled mean = 124), gradually declined on day 30 (pooled mean = 44), which persisted until day 360 (pooled mean = 10). Anti LPS IgG antibodies peaked on day 7 (pooled mean = 94). Thereafter, they decreased on day 30 (pooled mean = 85), and dropped further on days 90 (pooled mean = 51) and 180 (pooled mean = 47), and returned to baseline on day 360 (pooled mean = 32). Sensitivity analysis including data from young children (aged 2-5 years) showed very similar findings as in the primary analysis.

CONCLUSIONS

This study confirms that serological antibody (vibriocidal, CTB, and LPS) titers return to baseline levels within 1 year following clinical cholera, i.e., before the protective immunity against subsequent cholera wanes. However, this decay should not be interpreted as waning immunity because immunity conferred by cholera against subsequent disease lasts 3-10 years. Our study provides evidence for surveillance strategies and future research on vaccines and also demonstrates the need for further studies to improve our understanding of immunity against cholera.

A non-inferiority trial comparing two killed, whole cell, oral cholera vaccines (Cholvax vs. Shanchol) in Dhaka, Bangladesh

Bangladesh remains cholera endemic with biannual seasonal peaks causing epidemics. At least 300,000 severe cases and over 4,500 deaths occur each year. The available oral cholera vaccineshave not yet been adopted for cholera control in Bangladesh due to insufficient number of doses available for endemic control. With a public private partnership, icddr,b initiated a collaboration between vaccine manufacturers in Bangladesh and abroad. A locally manufactured Oral Cholera Vaccine (OCV) named Cholvax became available for testing in Bangladesh. We evaluated the safety and immunogenicity of this locally produced Cholvax (Incepta Vaccine Ltd) inexpensive OCV comparatively to Shanchol (Shantha Biotechnics-Sanofi Pasteur) which is licensed in several countries. We conducted a randomized non-inferiority clinical trial of bivalent, killed oral whole-cell cholera vaccine Cholvax vs. Shanchol in the cholera-endemic area of Mirpur, Dhaka, among three different age cohorts (1-5, 6-17 and 18-45 years) between April 2016 and April 2017. Two vaccine doses were given at 14 days apart to 2,052 healthy participants. No vaccine-related serious adverse events were reported. There were no significant differences in the frequency of solicited (7.31% vs. 6.73%) and unsolicited (1.46% vs. 1.07%) adverse events reported between the Cholvax and Shanchol groups. Vibriocidal antibody responses among the overall population for O1 Ogawa (81% vs. 77%) and O1 Inaba (83% vs. 84%) serotypes showed that Cholvax was non-inferior to Shanchol, with the non-inferiority margin of -10%. For O1 Inaba, GMT was 462.60 (Test group), 450.84 (Comparator group) with GMR 1.02(95% CI: 0.92, 1.13). For O1 Ogawa, GMT was 419.64 (Test group), 387.22 (Comparator group) with GMR 1.12 (95% CI: 1.02, 1.23). Cholvax was safe and non-inferior to Shanchol in terms of immunogenicity in the different age groups. These results support public use of Cholvax to contribute for reduction of the cholera burden in Bangladesh. ClinicalTrials.gov number: NCT027425581.

Protection afforded by previous Vibrio cholerae infection against subsequent disease and infection: A review

BACKGROUND

Cholera is an acute, diarrheal disease caused by Vibrio cholerae O1 or 139 that is associated with a high global burden.

METHODS

We analyzed the estimated duration of immunity following cholera infection from available published studies. We searched PubMed and Web of Science for studies of the long-term immunity following cholera infection. We identified 22 eligible studies and categorized them as either observational, challenge, or serological.

RESULTS

We found strong evidence of protection at 3 years after infection in observational and challenge studies. However, serological studies show that elevated humoral markers of potential correlates of protection returned to baseline within 1 year. Additionally, a subclinical cholera infection may confer lower protection than a clinical one, as suggested by 3 studies that found that, albeit with small sample sizes, most participants with a subclinical infection from an initial challenge with cholera had a symptomatic infection when rechallenged with a homologous biotype.

CONCLUSIONS

This review underscores the need to elucidate potential differences in the protection provided by clinical and subclinical cholera infections. Further, more studies are warranted to bridge the gap between the correlates of protection and cholera immunity. Understanding the duration of natural immunity to cholera can help guide control strategies and policy.

Vibrio cholerae at the Intersection of Immunity and the Microbiome

Vibrio cholerae is a noninvasive pathogen that colonizes the small intestine and produces cholera toxin, causing severe secretory diarrhea. Cholera results in long lasting immunity, and recent studies have improved our understanding of the antigenic repertoire of V. cholerae Interactions between the host, V. cholerae, and the intestinal microbiome are now recognized as factors which impact susceptibility to cholera and the ability to mount a successful immune response to vaccination. Here, we review recent data and corresponding models to describe immune responses to V. cholerae infection and explain how the host microbiome may impact the pathogenesis of V. cholerae In the ongoing battle against cholera, the intestinal microbiome represents a frontier for new approaches to intervention and prevention.

Immune responses to O-specific polysaccharide (OSP) in North American adults infected with Vibrio cholerae O1 Inaba

Background

Antibodies targeting O-specific polysaccharide (OSP) of Vibrio cholerae may protect against cholera; however, little is known about this immune response in infected immunologically naïve humans.

Methodology

We measured serum anti-OSP antibodies in adult North American volunteers experimentally infected with V. cholerae O1 Inaba El Tor N16961. We also measured vibriocidal and anti-cholera toxin B subunit (CtxB) antibodies and compared responses to those in matched cholera patients in Dhaka, Bangladesh, an area endemic for cholera.

Principal findings

We found prominent anti-OSP antibody responses following initial cholera infection: these responses were largely IgM and IgA, and highest to infecting serotype with significant cross-serotype reactivity. The anti-OSP responses peaked 10 days after infection and remained elevated over baseline for ≥ 6 months, correlated with vibriocidal responses, and may have been blunted in blood group O individuals (IgA anti-OSP). We found significant differences in immune responses between naïve and endemic zone cohorts, presumably reflecting previous exposure in the latter.

Conclusions

Our results define immune responses to O-specific polysaccharide in immunologically naive humans with cholera, find that they are largely IgM and IgA, may be blunted in blood group O individuals, and differ in a number of significant ways from responses in previously humans. These differences may explain in part varying degrees of protective efficacy afforded by cholera vaccination between these two populations.

Trial registration number

ClinicalTrials.gov NCT01895855.

Cholera is an acute, secretory diarrheal disease caused by Vibrio cholerae O1. There is a growing body of evidence that immune responses targetting the O-specific polysaccharide (OSP) of V. cholerae are associated with protecton against cholera. Despite this, little is known about immune responses targeting OSP in immunologically naive individals. Cholera affects populations in severely resource-limited areas. To address this, we assessed anti-OSP immune responses in North American volunteers experimentally infected with wild type V. cholerae O1 El Tor Inaba strain N16961. We found that antibody responses were largely IgM and IgA, cross-reacted to both Inaba and Ogawa serotypes, and correlated with vibriocidal responses. We found no association of responses to severity of disease, but did find that blood group O individuals mounted lower IgA fold-changes to OSP than did non-blood group O individuals. Individuals with blood group O are at particular risk for severe cholera, and are less well protected against cholera following oral vaccination. We also compared anti-OSP responses in previously unexposed individuals to responses in matched endemic zone patients, and found a number of significant differences. Such differences may explain in part the varying degrees of protective efficacy afforded by cholera vaccination between these two populations.

Bivalent oral cholera vaccination induces a memory B cell response to the V. cholerae O1-polysaccharide antigen in Haitian adults

The bivalent killed whole-cell oral cholera vaccine (BivWC) is being increasingly used to prevent cholera. The presence of O-antigen-specific memory B cells (MBC) has been associated with protective immunity against cholera, yet MBC responses have not been evaluated after BivWC vaccination. To address this knowledge gap, we measured V. cholerae O1-antigen MBC responses following BivWC vaccination. Adults in St. Marc, Haiti, received 2 doses of the BivWC vaccine, Shanchol, two weeks apart. Participants were invited to return at days 7, 21, 44, 90, 180 and 360 after the initial vaccination. Serum antibody and MBC responses were assessed at each time-point before and following vaccination. We observed that vaccination with BivWC resulted in significant O-antigen specific MBC responses to both Ogawa and Inaba serotypes that were detected by day 21 and remained significantly elevated over baseline for up to 12 months following vaccination. The BivWC oral cholera vaccine induces durable MBC responses to the V. cholerae O1-antigen. This suggests that long-term protection observed following vaccination with BivWC could be mediated or maintained by MBC responses.

Oral cholera vaccines are being increasingly used throughout the world as a key component of cholera prevention programs. While several recent studies suggest oral cholera vaccines may provide durable protection, the potential mechanism that generates this long lasting immune memory and protection are unknown. Unlike antibody and antibody secreting cell responses, memory B cells are thought to be an important part of the immune responses because although these cells do not produce antibody, they are long lived and can be rapidly stimulated to produce antibodies upon re-exposure to infection. Previous studies have shown that memory B cell responses to the Vibrio cholerae O-antigen are associated with protection against cholera infection. In this study, we found that oral cholera vaccine generated long lasting antibody and memory B cell responses to the Vibrio cholerae O-antigen that remained elevated for 6 to 12 months. These findings show that oral cholera vaccination does induce a strong memory B cell response, which could play a role in the generation and maintenance of long-term protection following BivWC vaccination.

Anti-O-specific polysaccharide (OSP) immune responses following vaccination with oral cholera vaccine CVD 103-HgR correlate with protection against cholera after infection with wild-type Vibrio cholerae O1 El Tor Inaba in North American volunteers

Background

Cholera is an acute voluminous dehydrating diarrheal disease caused by toxigenic strains of Vibrio cholerae O1 and occasionally O139. A growing body of evidence indicates that immune responses targeting the O-specific polysaccharide (OSP) of V. cholerae are involved in mediating protection against cholera. We therefore assessed whether antibody responses against OSP occur after vaccination with live attenuated oral cholera vaccine CVD 103-HgR, and whether such responses correlate with protection against cholera.

Methodology

We assessed adult North American volunteers (n = 46) who were vaccinated with 5 × 10⁸ colony-forming units (CFU) of oral cholera vaccine CVD 103-HgR and then orally challenged with approximately 1 × 10⁵ CFU of wild-type V. cholerae O1 El Tor Inaba strain N16961, either 10 or 90 days post-vaccination.

Principal findings

Vaccination was associated with induction of significant serum IgM and IgA anti-OSP and vibriocidal antibody responses within 10 days of vaccination. There was significant correlation between anti-OSP and vibriocidal antibody responses. IgM and IgA anti-OSP responses on day 10 following vaccination were associated with lower post-challenge stool volume (r = −0.44, P = 0.002; r = −0.36, P = 0.01; respectively), and none of 27 vaccinees who developed a ≥1.5 fold increase in any antibody isotype targeting OSP on day 10 following vaccination compared to baseline developed moderate or severe cholera following experimental challenge, while 5 of 19 who did not develop such anti-OSP responses did (P = 0.01).

Conclusion

Oral vaccination with live attenuated cholera vaccine CVD 103-HgR induces antibodies that target V. cholerae OSP, and these anti-OSP responses correlate with protection against diarrhea following experimental challenge with V. cholerae O1.

Trial registration

ClinicalTrials.gov NCT01895855

Cholera is a severe watery diarrheal disease, caused by pathogenic strains of V. cholerae. Protective immunity against cholera is serogroup specific, and serogroup specificity is determined by the O-specific polysaccharide (OSP) of V. cholerae lipopolysaccharide (LPS). Despite this, no previous work has directly assessed correlation of OSP-immune responses and protection against cholera. In this study, we assessed adult North American volunteer’s antibody responses targeting OSP after vaccination with live attenuated oral cholera vaccine CVD 103-HgR, and we assessed correlation of protection against cholera with such antibody responses. Oral vaccination was associated with the induction of significant IgM and IgA responses against OSP, and these responses correlated with vibriocidal responses. There was significant negative correlation of OSP responses and post-challenge stool volume, and none of the volunteers who developed an anti-OSP antibody responses of any isotype of ≥1.5 fold developed moderate or severe cholera following experimental challenge. In summary, vaccination with live attenuated oral cholera vaccine CVD 103-HgR induces antibodies that target V. cholerae OSP, and these responses highly correlate with protection against cholera.

Immunogenicity of a Glycoconjugate from Hydrazine-Detoxified Lipopolysaccharide of Vibrio cholerae O139

A glycoconjugate (dLPS-CBSA) from hydrazine-detoxified lipopolysaccharide (LPS) of Vibrio cholerae O139 and BSA was used for immunization of BALB/c mice. The immunogenicity (concentration of induced IgG antibodies) of the conjugate was determined by enzyme-linked immunosorbent assay. The highest level of LPS-specific IgGs was found in sera collected 2 weeks after the third immunization. Both IgM and IgG antibodies present in the anti-V. cholerae O139-specific sera showed long-lasting vibriocidal activity. The glycoconjugate also stimulated production of IL-4, IL-6, IFNγ, TNFα and IL-10. Immunization with the conjugate induced significant production of both Th1 and Th2 cytokine sets, indicating balanced Th1/Th2 immune response polarization. The quantitative analysis of total and LPS-specific IgM and IgG antibodies production by B lymphocytes (from both the spleen and the bone marrow) was performed by ELISPOT assay. From the analysis of antibodies produced directly by B lymphocytes in the bone marrow (of dLPS-CBSA immunized mice), we were able to identify the IgM-IgG switch in the antibodies produced.

O-Specific Polysaccharide-Specific Memory B Cell Responses in Young Children, Older Children, and Adults Infected with Vibrio cholerae O1 Ogawa in Bangladesh

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.

Immune responses to O-specific polysaccharide and lipopolysaccharide of Vibrio cholerae O1 Ogawa in adult Bangladeshi recipients of an oral killed cholera vaccine and comparison to responses in patients with cholera

Protective immunity to cholera is serogroup specific, and serogrouping is defined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). We characterized OSP-specific immune responses in adult recipients of an oral killed cholera vaccine (OCV WC-rBS) and compared these with responses in patients with cholera caused by Vibrio cholerae O1 Ogawa. Although vaccinees developed plasma immunoglobulin G (IgG), IgM, IgA antibody and antibody secreting cell (ASC, marker of mucosal response) to Ogawa OSP and LPS 7 days after vaccination, responses were significantly lower than that which occurred after cholera. Similarly, patients recovering from cholera had detectable IgA, IgM, and IgG memory B cell (MBC) responses against OSP and LPS on Day 30 and Day 90, whereas vaccinees only developed IgG responses to OSP 30 days after the second immunization. The markedly lower ASC and MBC responses to OSP and LPS observed among vaccinees might explain, in part, the lower protection of an OCV compared with natural infection.

The teleost humoral immune response

Over the past 10 years our knowledge of cellular and molecular dynamics of teleost humoral immunity has increased enormously to now include: the existence of multiple isotypes, affinity-driven modulation of antibody structure and function, the unique trafficking patterns of each stage of B cell differentiation (including the plasma blast, short-lived and long-lived plasma cell, and the memory cell). Unfortunately the work which has generated the bulk of this information has generally employed defined antigens rather than vaccines. Thus, the focus of this review is to relate these aspects of immunity that are requisite for a mechanistic understanding of the generation of prophylactic immunity to the necessary analysis of responses to vaccines and vaccine candidates.

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.

Frequency of reexposure to Vibrio cholerae O1 evaluated by subsequent vibriocidal titer rise after an episode of severe cholera in a highly endemic area in Bangladesh

Vibriocidal antibody is a marker of recent exposure to Vibrio cholerae O1 infection. We examined vibriocidal titers for 1 year after an episode of severe cholera in patients in Dhaka, Bangladesh; 16 of 53 (30%) patients had a fourfold or greater increase in vibriocidal titer between 6 and 12 months after an episode of severe cholera, suggesting reexposure to the organism. Among patients with rises in titers during follow-up, the patients initially infected with serotype Ogawa had earlier rises in titer than the patients initially infected with serotype Inaba. These data and others suggest that an episode of severe cholera protects against symptomatic disease for several years, but reexposure to the organism occurs frequently in an endemic area, with immunological boosts beginning as early as 6 months after severe disease. Repeated exposures to V. cholerae in endemic areas may be a necessary component for long-lasting protection against severe disease.

Immune responses to cholera in children

Cholera is a severe acute dehydrating diarrheal disease caused by Vibrio cholerae O1 or O139 infection, and is associated with significant mortality and morbidity globally. Although young children bear a high burden of the disease, currently available oral vaccines give a lower efficacy and shorter duration of protection in this group than in adults. According to the studies of natural infection, young children achieve comparable systemic anti-V. cholerae antigen-specific antibody, gut-homing antibody-secreting cell and memory B-cell responses as adults. Studies on innate and cell-mediated immune responses are lacking in children, and may offer important insights into differences in vaccine efficacy. The impact of host factors such as malnutrition, genetics and coinfection with other pathogens also remains to be fully defined.

Emerging trends in Lassa fever: redefining the role of immunoglobulin M and inflammation in diagnosing acute infection

BACKGROUND

Lassa fever (LF) is a devastating hemorrhagic viral disease that is endemic to West Africa and responsible for thousands of human deaths each year. Analysis of humoral immune responses (IgM and IgG) by antibody-capture ELISA (Ab-capture ELISA) and Lassa virus (LASV) viremia by antigen-capture ELISA (Ag-capture ELISA) in suspected patients admitted to the Kenema Government Hospital (KGH) Lassa Fever Ward (LFW) in Sierra Leone over the past five years is reshaping our understanding of acute LF.

RESULTS

Analyses in LF survivors indicated that LASV-specific IgM persists for months to years after initial infection. Furthermore, exposure to LASV appeared to be more prevalent in historically non-endemic areas of West Africa with significant percentages of reportedly healthy donors IgM and IgG positive in LASV-specific Ab-capture ELISA. We found that LF patients who were Ag positive were more likely to die than suspected cases who were only IgM positive. Analysis of metabolic and immunological parameters in Ag positive LF patients revealed a strong correlation between survival and low levels of IL-6, -8, -10, CD40L, BUN, ALP, ALT, and AST. Despite presenting to the hospital with fever and in some instances other symptoms consistent with LF, the profiles of Ag negative IgM positive individuals were similar to those of normal donors and nonfatal (NF) LF cases, suggesting that IgM status cannot necessarily be considered a diagnostic marker of acute LF in suspected cases living in endemic areas of West Africa.

CONCLUSION

Only LASV viremia assessed by Ag-capture immunoassay, nucleic acid detection or virus isolation should be used to diagnose acute LASV infection in West Africans. LASV-specific IgM serostatus cannot be considered a diagnostic marker of acute LF in suspected cases living in endemic areas of West Africa. By applying these criteria, we identified a dysregulated metabolic and pro-inflammatory response profile conferring a poor prognosis in acute LF. In addition to suggesting that the current diagnostic paradigm for acute LF should be reconsidered, these studies present new opportunities for therapeutic interventions based on potential prognostic markers in LF.

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.

Antigen-specific memory B-cell responses in Bangladeshi adults after one- or two-dose oral killed cholera vaccination and comparison with responses in patients with naturally acquired cholera

The mediators of protective immunity against cholera are currently unknown, but memory B-cell responses may play a central role in facilitating long-term and anamnestic responses against Vibrio cholerae, the cause of cholera. We compared memory B-cell responses in adults with natural cholera in Bangladesh (n = 70) to responses in Bangladeshi adults after one-dose (n = 30) or two-dose (n = 30) administration of an oral killed cholera vaccine, WC-rBS (Dukoral; Crucell), assessing the responses at the acute stage of disease or prevaccination and then on days 3, 30, 90, 180, 270, and 360. Individuals with natural cholera developed prominent vibriocidal and plasma anti-cholera toxin B subunit (CtxB) and lipopolysaccharide (LPS) IgG and IgA responses, but these responses returned to baseline by 1 year of follow-up. Vaccinees developed plasma anti-CtxB and anti-LPS IgG and IgA responses that were generally comparable to those in individuals recovering from natural disease, but vibriocidal responses were lower in vaccinees than in infected patients. Individuals recovering from natural disease developed memory B-cell IgG and IgA anti-CtxB and anti-LPS responses by day 30, and these responses were detectable through at least days 180 to 360. In contrast, we detected no IgA or IgG memory B-cell responses to LPS in vaccinees; anti-CtxB IgA responses were only detectable on day 30, and anti-CtxB IgG responses were detectable until days 90 to 180, compared to days 270 to 360 in patients. These findings may explain in part the relatively short-term protection afforded by oral cholera vaccination compared to natural disease.