CD79A and infection: In addition to counteracting pathogenic infections at mucosal surfaces, IgA can establish and stabilize intestinal commensal colonization and internal symbiosis.301 Specifically, the commensal colonization factor system in B. fragilis modulates the expression of capsular polysaccharide on the surface of the bacteria to induce close binding to IgA, which makes bacteria themselves enter the intestinal mucus layer and become a stable component of the gut microbiome.71