Akkermansia muciniphila induces intestinal adaptive immune responses during homeostasis

Context shapes anticommensal immunity The gut bacterium Akkermansia muciniphila is associated with protection from obesity, enhanced wound healing, and augmented antitumor responses. Ansaldo et al. found that this microbe induces antigen-specific immunoglobulin G1 (IgG1) antibodies generated by B cells with CD4 + T cell help. This is in contrast to most anticommensal responses, which involve the T cell–independent production of IgA antibodies. In a gnotobiotic setting in which all components of the microbiome are defined, A. muciniphila –specific T cells expanded only when A. muciniphila was present. The T cells primarily displayed a phenotype associated with B cell help. However, in mice with a conventional gut microbiota, other proinflammatory A. muciniphila –specific T cell populations also expanded. Thus, anti– A. muciniphila immunity is context dependent, which may explain the variable immune responses to this microbe reported in patients. Science , this issue p. 1179