Drawing on the mechanisms described in other types of monoclonal immunoglobulin-associated C3GN (8, 13), we speculate that IgM-kappa free light chains, derived from the lymphoma, may function as mini-autoantibodies targeting the N-terminus of CFH, thereby disrupting its cofactor activity, overactivating the alternative pathway of the complement system and inhibiting the function of complement regulatory proteins. The gene discussed is CFH; the disease is lymphoma.