FCGR2B and systemic lupus erythematosus: Indeed, a synthetic derivative of the vitamin B9 metabolite 6-FP (i-6FP) has been used to inhibit MAIT cell activation and improve the course of the autoimmune disease lupus in FcγRIIb−/− mice, a spontaneous model of systemic lupus erythematosus in which MAIT cells have been shown to enhance autoantibody production and tissue inflammation (45).