In summary, the presence of IgA against Candida albicans in plasma from patients with plaque psoriasis without clinical signs of infection identifies subjects that have been exposed to this microbe, which preferentially activates skin-homing CLA+ T cells to secrete IL17F and IL17A, two cytokines that are clinically demonstrated to be relevant in psoriasis immunopathogenesis. The gene discussed is IL17A; the disease is infection.