Inhibition of immune haemolysis by a serum factor found in C3-deficient subjects.
A serum factor, which inhibits haemolysis of the buffer control used in a C3 haemolytic assay, was found in a C3-deficient subject (C3D). Since the buffer control consisted of EAC142, C5 and C6-9 reagent (C6-9R, prepared by treatment of guinea-pig serum with KSCN and hydrazine hydrate), the factor seems to be an inhibitor of C3-independent immune haemolysis. Gel filtration and CM cellulose column chromatography of C3D serum suggested that the inhibitor may be C8. The inhibition was not observed in C8-depleted C3D serum. Furthermore, isolated C8 was found to inhibit haemolysis of EAC142 by C5 and C6-9R in a dose-dependent fashion. Thus, C8 was found to be an inhibitor of C3-independent immune haemolysis in the assay. Further studies revealed that C8 also inhibits haemolysis of EAC142 by C3, C5 and C6-9R (C3 assay system) or that of EAC1423 by C5 and C6-9R (C5 assay system), indicating that C3 or C5 haemolytic activity can be underestimated by the presence of C8 in a sample. C8 did not inhibit haemolysis in the assay system when isolated C6-C9 of human origin were used, but did inhibit haemolysis when isolated C6-C9 of guinea-pig origin was used instead of C6-9R. Thus, it was suggested that the incompatibility of human C8 with guinea-pig C6-C9 might be responsible for this phenomenon. Additional experiments for the mechanism clearly showed that human C8 inhibits the haemolysis of EAC1-7 (EA bearing human C1-C5 and guinea-pig C6 and C7) by guinea-pig C8 and C9 by binding to EAC1-7 prior to guinea-pig C8.
Kitamura
H
H
Department of Immunology, Center for Adult Diseases, Osaka, Japan.
Tsuboi
M
M
D000818:Animals; D003176:Complement C3 / Q000172:deficiency*; D003183:Complement C6 / Q000502:physiology; D003185:Complement C8 / Q000502:physiology*; D003186:Complement C9 / Q000502:physiology; D004912:Erythrocytes / Q000276:immunology; D005260:Female; D006168:Guinea Pigs; D006461:Hemolysis / Q000187:drug effects*; D006801:Humans
D003176:Complement C3; D003183:Complement C6; D003185:Complement C8; D003186:Complement C9