[The complement system. Normal values and congenital deficiencies in the adult Mexican population].

Five hundred mexican mestizos, healthy blood donors were evaluated regarding the hemolytic activity of their serum, to assess the function of the complement (C) system. One of them was hypocomplementemic and his serum was unable to promote hemolysis by either classical or alternative pathway. It had normal protein concentrations of C3 and C4, as well as immunoreactive C1, C4, C5, C6, C7 and C8, and lytic factor D. Factor B was not recognizable. It is possible that a genetic deficiency linked to genes codifying for class III products of the major histocompatibility complex is responsible for our findings.