C3 and rheumatoid arthritis: Additionally, it has been evidenced that abnormal expression of FTO in peripheral blood mononuclear cells (PBMCs) from RA patients is a risk factor for RA and is closely related to disease activity indicators [such as DAS28-erythrocyte sedimentation rate (ESR), DAS28-C-reactive protein (CRP), complement C3 (C3), immunoglobulin G (IGG), platelet-lymphocyte ratio (PLR), and lymphocyte-monocyte ratio (LMR)] (16).