The production of immunoglobulin A (IgA) in mammals exceeds all other isotypes, and it is
mostly exported across mucous membranes. The discovery of IgA and the realization that it
dominates humoral mucosal immunity, in contrast to the IgG dominance of the systemic
immune system, was early evidence for the distinct nature of mucosal immunology. It is now
clear that IgA can function in high-affinity modes for neutralization of toxins and pathogenic
microbes, and as a low-affinity system to contain the dense commensal microbiota within the …