Weil, A. A. | Search bioRxiv

bioRxiv2018

Cognate T and B cell interaction and association of Follicular helper T cells with B cell responses in Vibrio cholerae O1 infected Bangladeshi adults

Vibrio cholerae O1 can cause life threatening diarrheal disease if left untreated. A long lasting immune response, producing 3-5 years of protection from subsequent, symptomatic disease following natural infection, is mediated by B cell mediated humoral immunity. T cells can play critical roles in inducing such immunity. However, the mechanism of T cell dependent B cell maturation and whether a key sub-population of T cells are involved is not well established in cholera. We hypothesized that a specific population of T cells, follicular helper T (Tfh) cells, are involved in B cell maturation following cholera; we used flow cytometry, culture and colorimetric assays to address this question. We found that V. cholerae infection induces significant increase in circulating Tfh cells expressing B cell maturation associated protein CD40L early in disease. The increased Tfh cells expressing CD40L recognize cholera toxin most prominently, with lessened responses to two antigens tested, V. cholerae membrane preparation (MP) and Vibrio cholerae cytolysin (VCC). We further showed that early induction of Tfh cells and CD40L was associated with later memory B cell responses to same antigens. Lastly, we demonstrated in vitro that Tfh cells isolated after cholera can stimulate class switching of cocultured, isolated B cells from patients with cholera, leading to production of the more durable IgG antibody isotype. These studies were conducted on circulating Tfh cells; future studies will be directed at examining role of Tfh cells during cholera directly in the gut mucosa of biopsied samples, at the single cell level if feasible.

immunology↗

bioRxiv2017

Vibrio cholerae genomic diversity within and between patients

Cholera is a severe, waterborne diarrheal disease caused by toxin-producing strains of the bacterium Vibrio cholerae. Comparative genomics has revealed \"waves\" of cholera transmission and evolution, in which clones are successively replaced over decades and centuries. However, the extent of V. cholerae genetic diversity within an epidemic or even within an individual patient is poorly understood. Here, we characterized V. cholerae genomic diversity at a micro-epidemiological level within and between individual patients from Bangladesh and Haiti. To capture within-patient diversity, we isolated multiple (8 to 20) V. cholerae colonies from each of eight patients, sequenced their genomes and identified point mutations and gene gain/loss events. We found limited but detectable diversity at the level of point mutations within hosts (zero to three single nucleotide variants within each patient), and comparatively higher gene content variation within hosts (at least one gain/loss event per patient, and up to 103 events in one patient). Much of the gene content variation appeared to be due to gain and loss of phage and plasmids within the V. cholerae population, with occasional exchanges between V. cholerae and other members of the gut microbiota. We also show that certain intra-host variants have phenotypic consequences. For example, the acquisition of a Bacteroides plasmid and nonsynonymous mutations in a sensor histidine kinase gene both reduced biofilm formation, an important trait for environmental survival. Together, our results show that V. cholerae is measurably evolving within patients, with possible implications for disease outcomes and transmission dynamics.\n\nAuthor SummaryVibrio cholerae is the etiological agent of cholera, a severe diarrheal disease endemic to Bangladesh and responsible for global outbreaks, including one ongoing in Haiti. Certain bacterial pathogens can evolve and diversify within the human host, often altering virulence and antibiotic resistance. However, most examples of within-host evolution have come from chronic infections, in which the pathogen has sufficient time to mutate and diversify, and little attention has been paid to more acute infections such as the one caused by V. cholerae. The goal of this study was to measure the extent of within-host evolution of V. cholerae within individual infected patients. By sequencing multiple bacterial isolates_from each of eight patients from Bangladesh and Haiti, we found that cholera patients can harbor a diverse population of V. cholerae. As expected for an acute infection, this diversity is limited, ranging from zero to three point mutations (single nucleotide variants) per patient. However, gene gain/loss events are more prevalent than point mutations, occurring in every single patient, and sometimes involving the transfer of dozens of genes on plasmids. Even if rare, point mutations and gene gain/loss events may be maintained by natural selection, and can alter clinically-and environmentally-relevant phenotypes such as biofilm formation. Therefore, within-patient evolution has the potential to impact clinical and epidemiological outcomes. Together, our results demonstrate that within-patient evolution may be a general feature of both acute and chronic infections, and that gene gain/loss may be an important but under-appreciated feature of within-host evolution.

microbiology↗