Autoantibodies Targeting Ficolin‐2 in Systemic Lupus Erythematosus Patients With Active Nephritis

Systemic lupus erythematosus (SLE) is a multisystem inflammatory disease characterized by the production of various autoantibodies. The aim of this study was to investigate the presence of anti–ficolin‐2 antibodies in SLEpatients and to evaluate the association between the levels of these autoantibodies, clinical manifestations, and disease activity. This is a comparative study using a cohort of 165 SLEpatients and 48 healthy subjects. SLEpatients were further divided into 2 groups (low disease activity [SLEDisease Activity Index (SLEDAI) score ≤4, n = 88] and high disease activity [SLEDAIscore >4, n = 77]). Clinical manifestations were defined according to the physician in charge. Active lupus nephritis (LN) was documented by kidney biopsy. Detection of anti–ficolin‐2 antibodies was performed by enzyme‐linked immunosorbent assay. Levels of anti–ficolin‐2 autoantibodies were significantly higher in SLEpatients as compared to healthy subjects and associated with SLEDAIscore. They were found to be positive in 61 of 165 SLEpatients (37%). The presence of anti–ficolin‐2 antibodies was significantly related only to renal involvement, with a very high prevalence (86%) of anti–ficolin‐2 antibodies in SLEpatients with active LN. Patients with active proliferative LNhad significantly more positive anti–ficolin‐2 antibodies than those with nonproliferative LN. The combination of anti–ficolin‐2, anti–ficolin‐3, and anti‐C1q demonstrated a very high specificity (98%) for the diagnosis of active LN. Our results support the usefulness of anti–ficolin‐2 as a complementary serologic biomarker for the diagnosis of active lupus with renal manifestations.