A recent study by Vogt et al., using highly specific antibody against a cleavage neoepitope in C4d, identified pigment epithelium-derived factor (PEDF) from synovial fluid of rheumatoid arthritis patients as an activator of classical complement pathway, which belongs to the serine proteinase inhibitor family. The gene discussed is SERPINF1; the disease is rheumatoid arthritis.