Here, we combined biochemical and genetic analyses to explore associations between MASP/MAP proteins, SLE manifestations and autoantibody specificities.<h4>Methods</h4>Serum concentrations of MASP-3, MAP-1 and MASP-2 were measured using ELISA in Swedish patients with SLE (n=522) and population-based matched controls (n=322). Here, MASP1 is linked to systemic lupus erythematosus.