title: C56 formation in the reaction mixture of isolated complement components through the classical complement pathway.
abstract: The mechanism of hemolysis of unsensitized erythrocytes by a mixture of 9 isolated, human-derived complement components, C1s, C4, C2, C3, C5, C6, C7, C8 and C9 (C1s-C9) was studied. Of the tested erythrocytes, guinea pig erythrocytes (Egp) were the most susceptible to lysis by C1s-C9, followed by human and sheep erythrocytes. Contamination of the isolated complement components by C56 was ruled out. It was determined that a factor was generated in the reaction mixture of C1s, C4, C2, C3, C5 and C6 (C1s-C6), which had lytic activity against Egp when C7, C8 and C9 were added. We found that the lytic factor was similar to C56 in the following properties: (1) the activity of the lytic factor decreased when incubated with isolated C7 prior to its reaction with Egp; (2) the lytic factor did not bind to Egp by itself but it did bind in the presence of C7; (3) EDTA did not have any inhibitory effect on the lytic factor; (4) the activity of the lytic factor decreased by treatment with anti-C5 and anti-C6 but not by treatment with anti-C3 and anti-C4, and (5) gel filtration of the reaction mixture (C1s-C6) indicated that the elution volumes of the lytic factor and of isolated C56 were similar. Thus, it is likely that C56 is generated in the reaction mixture of C1s-C6 and the lytic factor binds to unsensitized erythrocytes together with C7, to form an intermediate EC567 which is susceptible to lysis by the action of C8 and C9.
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D002850:Chromatography, Gel; D003167:Complement Activation; D003182:Complement C5 / Q000502:physiology*; D003183:Complement C6 / Q000502:physiology*; D003184:Complement C7; D003171:Complement Pathway, Classical; D003165:Complement System Proteins / Q000276:immunology / Q000502:physiology; D006168:Guinea Pigs; D006461:Hemolysis; D006801:Humans; D008274:Magnesium / Q000494:pharmacology
chemical_list: D000906:Antibodies; D003182:Complement C5; D003183:Complement C6; D003184:Complement C7; D003165:Complement System Proteins; D008274:Magnesium