SLE is a systemic autoimmune disease that affects the skin, joints, kidney, lung, heart and brain. SLE patients exhibit a characteristic rash that gives the disease its name. The rash is red in color (erythematous) and is concentrated on the cheeks such that some patients have a “wolfish” appearance (lupus is Latin for “wolf”). Multiple elements of the immune system may be disrupted in SLE patients such that these individuals are usually vulnerable to opportunistic infections.
A signature feature of SLE is the production of high levels of “anti-nuclear” autoantibodies, which are directed against dsDNA and small nuclear proteins. Affected individuals may also produce auto-antibodies to RBCs, platelets, leukocytes, IgG, membrane phospholipids, and clotting factors. Auto-antibodies specific for RBCs and platelets can lead to complement-mediated lysis, resulting in hemolytic anemia and thrombocytopenia, respectively. When immune complexes of auto-antibodies with various nuclear antigens are deposited along the walls of small blood vessels, a type III hypersensitivity reaction develops. The complexes activate the complement system and generate membrane-attack complexes and complement fragments (C3a and C5a) that damage the wall of the blood vessel, resulting in vasculitis and glomerulonephritis.