We discuss autoimmune diseases such as ocular cicatricial pemphigoid, pemphigus, discoid and systemic lupus erythematosus, and thyroid-associated orbitopathy, focusing on the roles of T helper cell subsets, pro-inflammatory cytokines (IL-1β, IL-6, IL-17, TNF-α), and autoantibody-mediated complement activation. The gene discussed is IL17A; the disease is pemphigus.