Deficiencies of the complement system in man.

Deficiencies of components of the complement system in man are described. Clq was reconstituted in patients with severe combined immunodeficiency after bone marrow transplantation. Clr deficiency is associated with vascular disease and upper respiratory infections. Reconstitution of complement occurred in one patient with Clr deficiency after kidney transplantation. Our C2-deficient patient who developed systemic lupus erythematosus had elevated levels of C3. Following blood transfusion, ie by providing C2, dramatic activation of complement occurred in vivo.