Bacteria That Cause Enteric Diseases Stimulate Distinct Humoral Immune Responses

Biofilm formation on human immune cells is a multicellular predation strategy of Vibrio cholerae

Biofilm formation is generally recognized as a bacterial defense mechanism against environmental threats, including antibiotics, bacteriophages, and leukocytes of the human immune system. Here, we show that for the human pathogen Vibrio cholerae, biofilm formation is not only a protective trait but also an aggressive trait to collectively predate different immune cells. We find that V. cholerae forms biofilms on the eukaryotic cell surface using an extracellular matrix comprising primarily mannose-sensitive hemagglutinin pili, toxin-coregulated pili, and the secreted colonization factor TcpF, which differs from the matrix composition of biofilms on other surfaces. These biofilms encase immune cells and establish a high local concentration of a secreted hemolysin to kill the immune cells before the biofilms disperse in a c-di-GMP-dependent manner. Together, these results uncover how bacteria employ biofilm formation as a multicellular strategy to invert the typical relationship between human immune cells as the hunters and bacteria as the hunted.

Know your enemy or find your friend?-Induction of IgA at mucosal surfaces

Most antibodies produced in the body are of the IgA class. The dominant cell population producing them are plasma cells within the lamina propria of the gastrointestinal tract, but many IgA-producing cells are also found in the airways, within mammary tissues, the urogenital tract and inside the bone marrow. Most IgA antibodies are transported into the lumen by epithelial cells as part of the mucosal secretions, but they are also present in serum and other body fluids. A large part of the commensal microbiota in the gut is covered with IgA antibodies, and it has been demonstrated that this plays a role in maintaining a healthy balance between the host and the bacteria. However, IgA antibodies also play important roles in neutralizing pathogens in the gastrointestinal tract and the upper airways. The distinction between the two roles of IgA - protective and balance-maintaining - not only has implications on function but also on how the production is regulated. Here, we discuss these issues with a special focus on gut and airways.

The murine neonatal Fc receptor is required for transport of immunization-induced C. difficile-specific IgG to the gut and protection against disease but does not affect disease susceptibility

The pathology associated with C. difficile disease is caused in large part by TcdB, an intracellular bacterial toxin that inactivates small GTPases. Despite C. difficile causing an enteric disease, anti-toxin IgG is a clear correlate of protection against infection-associated pathology. Immunization with TcdB-based immunogens or passive transfer of monoclonal antibodies specific for the TcdB carboxy-terminal domain (CTD) confers protection following C. difficile infection. Whether the mechanism by which circulating IgG is delivered to the gut depends on specific receptor-mediated transport or is solely reflective of infection-induced damage to the gut remains unclear. Herein, we tested the hypothesis that neonatal Fc receptor (FcRn) is required for delivery of systemic TcdB-specific IgG to the gut and protection against C. difficile-associated pathology. FcRn-expressing mice and FcRn-deficient littermates were immunized subcutaneously with Alhydrogel adjuvant-adsorbed CTD before challenge with live C. difficile spores. FcRn was required for delivery of systemic TcdB-specific IgG to the gut, and for vaccine-induced protection against C. difficile associated disease. The lack of FcRn expression had minimal effects on composition of the gut microbiome and did not affect susceptibility to C. difficile infection in non-immunized mice. In further experiments intraperitoneal injection FcRn-deficient mice with immune sera led to transport of protective IgG to the gut independently of infection confirming a reported method of bypassing the FcRn. Our results reveal an FcRn-dependent mechanism by which systemic immunization-induced IgG protects the gut during enteric C. difficile infection. These findings may be beneficial for targeting of C. difficile -specific IgG to the gut.