Alternative pathway for complement activation triggered by human liver plasma membranes

Liver plasma membranes (LPM) prepared from normal hepatocytes by centrifugation in sucrose discontinuous gradient, are capable of haemolysing PNH-like cells in the presence of complement or complement plus EGTA or MG2+ ions. In contrast, EDTA or Ca2+ ions inhibit the lysis. The total complement lytic activity is reduced by some 40% when fresh serum is incubated with LPM, whereas the total amount of C4 remains constant. The cross-immunoelectrophoresis studies of fresh serum incubated with LPM demonstrate the appearance of C3 breakdown products, which suggests the activation of the alternative complement pathway. In contrast, the sucrose test, which proceeds mainly through the classical complement pathway, is inhibited by LPM. The possible role of complement in liver disease is discussed.