PNH E have an unexplained membrane defect making them highly susceptible to complement (C) lysis. Studies by others have found: 1) equal binding of antibody (Ab), C1 and C4, and similar C2 Tmax and decay, on PNH and normal human E; 2) markedly increased C3 binding by PNH E relative to Ab or C4 binding; 3) supranormal lysis per unit of C3 bound; 4) comparable numbers of 10nm electron microscopic (EM) ring lesions on lysed PNH and normal E membranes; and 5) in the presence of fluid phase and C5–C9, increased lysis of and C5 binding to PNH E, but equal lysis of PNH and normal E for a given quantity of C5 bound.

Our studies sought to further define the lytic behavior of PNH E. The PNH patients studied included cases with predominant populations of highly C-sensitive E (“type III”), or with intermediately sensitive E (“type II”), or with mixtures of E types.

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