THE INITIATION AND ENHANCEMENT OF HUMAN RED CELL LYSIS BY ACTIVATORS OF THE FIRST COMPONENT OF COMPLEMENT AND BY FIRST COMPONENT ESTERASE; STUDIES USING NORMAL RED CELLS AND RED CELLS FROM PATIENTS WITH PAROXYSMAL NOCTURNAL HEMOGLOBINURIA.

* Submitted for publication July 31, 1964; accepted December 3, 1964. This work was supported in part by the Helen and Joseph Regenstein Foundation. t John and Mary R. Markle Scholar in Academic Medicine. Address requests for reprints to: Dr. Stanley Yachnin, Department of Medicine, The University of Chicago, 950 East 59th St., Chicago 37, Ill. t Operated by the University of Chicago for the United States Atomic Energy Commission. 1 The following abbreviations are used: C', complement; anti-C', anticomplementary; C'Hw, 50% hemolytic unit of complement; C'1, C'2, C'3, C'4, the first, second, third, or fourth component of complement; R1, R2, R3, R4, RP, serum lacking the designated complement component or properdin; C'la, C'2a, activated first or second complement components; C'lq, C'ls, subcomponents of the first component of complement; C'3a, C'3b, C'3c, C'3d, four factors that together comprise total third component activity; E, erythrocytes; S, antigen site on the red cell membrane; A, antibody or amboceptor; EA, sensitized erythrocytes (usually sheep red cells); EAC'. , sensitized erythrocytes bearing complement components as designated by numerical subcripts; E*, red cells irreversibly damaged by the action of complement; S*, red cell membrane site damaged by complement; C'1EI, the serum inhibitor of first component esterase; PNH, paroxysmal nocturnal hemoglobinuria; PNHE, red cells from patients with paroxysmal nocturnal hemoglobinuria; NHE, normal human red cells; poly I, poly A, poly U, poly C, biosynthetic homopolymers of inosinic, adenylic, uridylic, and cytidylic acids; poly (I + A), poly (I + C), double stranded hydrogen bonded helices composed of equimolar amounts of polyinosinic and polyadenylic acids or polyinosinic and polycytidylic acids; EDTA, ethylenediamine tetraacetate. C'lq (11 S) (3) portion of the C'1 molecule, thereby preventing the attachment of C'1 to the sensitized red cell (4). Addition of poly I to C' also results in inactivation of C'4. The latter effect is mediated via activation of the C'1 molecule and the conversion of C'1 proesterase (C'ls) to the active esterase form (5). This conclusion, although based on indirect evidence, is strengthened by the observation that poly I shares with C'la and purified C'1 esterase the ability to evoke vascular permeability in guinea pig skin (6, 7). On the basis of this evidence an analogy has been drawn between the effects of poly I on the C' system, and those of antigen-antibody complexes or heat aggregated gammaglobulin (5, 6). After having thus defined in detail the mechanism of poly I inhibition of immune red cell lysis, attention was turned to the effects of this material on the hemolysis in vitro of red cells from patients afflicted with PNH. There can be little doubt that the C' system participates in PNHElysis, since removal or inactivation of any one of the four major components of C' will destroy the capacity of human serum to support PNHElysis (8). It was naturally anticipated that poly I, being an anti-C' substance, would inhibit the PNHE hemolytic system. In fact, it was found that the addition of poly I to human serum provoked substantial stimulation of PNHEhemolysis. In addition it was found that the addition of poly I to human serum could, under appropriate conditions, induce substantial in vitro hemolysis of normal human erythrocytes (NHE). Other activators of C'1, as well as C'la and C'1 esterase, behaved in a similar manner. This paper describes these hemolytic systems with respect to kinetics, pH optima, cat-