Cooperative control of IgA synthesis and secretion by MZB1 and the J chain

, loss of MZB1, the J chain, or both altered IgA abundance and form, differentially affected susceptibility to DSS-induced colitis, and reshaped gut microbiota composition. These findings define a cooperative mechanism by which MZB1 and the J chain orchestrate IgA biogenesis, with MZB1 regulating quantity and the J chain determining quality, and reveal how variation in IgA form and abundance contributes to mucosal immune protection.