Interpreting immunoglobulin A evidence for the mucosal origins of rheumatoid arthritis autoimmunity

Immunoglobulin A (IgA) links barrier immunity, preclinical autoimmunity, and inflammatory effector pathways in rheumatoid arthritis (RA), but these associations support different biological and clinical claims. This critical narrative review synthesizes selected human, structural, cellular, and animal studies through six dimensions: molecular identity, compartmental enrichment, local synthesis, clonal continuity, temporal order, and perturbation. Evidence coverage is distinguished from study credibility. Three judgments organize the synthesis. First, secretory component (SC)-associated anti-citrullinated protein antibody (ACPA) signals require isotype resolution: early-RA depletion experiments implicate IgM, and SC association does not by itself locate initial activation. Second, IgA1-associated progression and stronger IgA2-mediated macrophage activation suggest that predictive and effector features may differ, but comparisons across designs do not establish subclass-specific clinical roles. Third, absence of detectable autoantibodies in the tested intestinal secretions constrains luminal output in the sampled RA populations; disease stage, treatment, and antibody-specific analytical sensitivity limit extrapolation to disease initiation. Antibody assembly and longitudinal clonal relationships provide complementary information without automatically establishing anatomical origin. Clinically, SC-ACPA may enrich risk among symptomatic IgG ACPA-positive individuals, including an RF-negative subgroup. Additional diagnostic or prognostic information from IgA-RF and IgA-ACPA is assay- and decision-dependent, and current evidence does not establish IgA-guided treatment selection. A clinical schematic separates target populations, observed associations, and proposed actions requiring validation. The framework connects each interpretation to its supporting observation, limitations, and next discriminating study.