A 42-year-old Caucasian man had SLE since 1992, manifested by malar rash, arthritis, serositis, proteinuria, leukopenia, lymphopenia, thrombocytopenia, positive immunology for ANA (1:640, homogenous/speckled pattern), anti-dsDNA, lupus anticoagulant, anticardiolipin, anti-Smith, anti-RNP, low C3, and C4. Here, C3 is linked to arthritic joint disease.