Diversification of memory B cells drives the continuous adaptation of secretory antibodies to gut microbiota

Secretory immunoglobulin A (SIgA) shields the gut epithelium from luminal antigens and contributes to host-microbe symbiosis. However, how antibody responses are regulated to achieve sustained host-microbe interactions is unknown. We demonstrate that mice and humans exhibited longitudinal persistence of clonally related B cells in the IgA repertoire despite major changes in the microbiota during antibiotic treatment or infection. Memory B cells re-circulated between inductive compartments and were clonally related to plasma cells in gut and mammary glands. Our findings suggest that continuous diversification of memory B cells constitutes a central process to establish symbiotic host-microbe interactions and offer an explanation of how maternal antibodies are optimized throughout life to protect the newborn.