C3 and systemic lupus erythematosus: There are also contradictory reports of patients with juvenile onset SLE [24-27], neuropsychiatric SLE [3,28,29], lupus nephritis class V [3,27,30], high disease activity [15,16,26,31] and low levels of complement component 3 (C3) or complement component 4 (C4) [16,17,22,32].