Paroxysmal nocturnal hemoglobinuria. Increase in proteins of the alternative complement pathway

: Increased activity of the complement alternative pathway proteins C3, B and H was found in the sera of 16 patients with paroxysmal nocturnal haemoglobinuria (PNH). This increased activity might depend on protein hypersynthesis secondary to in vivo low-grade complement consumption by abnormal erythrocytes in PNH patients, despite the fact that serum levels of C3d were found to be normal. B and H activities were directly related; however, the B/H ratio was higher in patients whose sera had been taken early after an episode of haemoglobinuria. Activation of the alternative pathway, which is known to result in vitro lysis of PNH erythrocytes, only accounts for part of the events leading to chronic haemolysis and haemoglobinuria in vitro.