Relationship of complement activation route with clinical manifestations in Japanese patients with systemic lupus erythematosus: a retrospective observational study.

OBJECTIVES: To assess the relationship between the complement activation route and clinical manifestations in systemic lupus erythematosus (SLE).

METHODS: Patients with SLE in whom complement activation occurred were divided into two groups: those in whom the complement system was mainly activated through the classical pathway (low serum C3 and C4 levels; CP group); and those in whom the complement system was solely activated through the alternative pathway (low serum C3 with normal C4 levels; AP group). Clinical manifestations were compared between the groups.

RESULTS: The CP group had higher frequencies of arthritis, serositis, and nephritis, and a higher prevalence of anti-DNA antibodies compared to the AP group (arthritis: 50.0% vs. 13.0%, p = 0.0014; serositis: 37.5% vs. 13.0%, p = 0.0257; nephritis: 63.6% vs. 21.7%, p = 0.0003; anti-DNA antibodies: 73.9% vs. 30.4%, p = 0.0001). In contrast, the AP group had a higher frequency of anti-phospholipid (anti-PL) antibodies and a higher prevalence of antiphospholipid syndrome (APS) (anti-PL antibodies: 70.6% vs. 37.3%, p = 0.0136; APS: 39.1% vs. 5.7%, p < 0.0001).

CONCLUSIONS: Our results suggest that a different complement system mechanism may act in the pathogenesis of APS in patients with SLE.