Perdiguero, Pedro, Martín-Martín, Alba, Benedicenti, Ottavia, Díaz-Rosales, Patricia, Morel, Esther, Muñoz-Atienza, Estefanía, García-Flores, Mónica, Simón, Rocío, Soleto, Irene, Cerutti, Andrea, and Tafalla, Carolina
Immunoglobulin D (IgD) is an ancient antibody with dual membrane-bound and fluid-phase antigen receptor functions. The biology of secreted IgD remains elusive. Here, we demonstrate that teleost IgD+IgM−plasmablasts constitute a major lymphocyte population in some mucosal surfaces, including the gut mucosa. Remarkably, secreted IgD binds to gut commensal bacteria, which in turn stimulate IgD gene transcription in gut B cells. Accordingly, secreted IgD from gut as well as gill mucosae, but not the spleen, show a V(D)J gene configuration consistent with microbiota-driven clonal expansion and diversification, including mild somatic hypermutation. By showing that secreted IgD establishes a mutualistic relationship with commensals, our findings suggest that secreted IgD may play an evolutionary conserved role in mucosal homeostasis.