Teleost IgD+IgM− B cells mount clonally expanded and mildly mutated intestinal IgD responses in the absence of lymphoid follicles

Acknowledgments Lucia González and Beatriz Abós are greatly acknowledged for technical assistance. This work was supported by the European Research Council (ERC Consolidator Grant 725061), the Spanish Ministry of Science, Innovation, and Universities (project AGL2017-85494-C2-1-R), and the Comunidad de Madrid (grant 2016-T1/BIO-1672).
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.
European Commission
Ministerio de Ciencia, Innovación y Universidades (España)
Comunidad de Madrid
Depto. de Genética, Fisiología y Microbiología
Fac. de Ciencias Biológicas
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