Sera genetically deficient in either the α-γ or the β-subunit of complement component C8 virtually lack haemolytic activity. We have studied the formation and the structural organization of the soluble terminal complement complex (TCC) assembled in these sera following activation with cobra venom factor (CVF). The TCC concentration in the activated C8α-γ and C8β-deficient samples was 0.2% and 4%, respectively, when compared with zymosan-activated normal serum. TCC was purified from the activated C8β- deficient samples by affinity chromatography and analysed by immunoblotting and enzyme immunoassay. No C8β was detected in one TCC preparation, while 7% of the normal level was present in the other. The level of the other terminal components, including that of C8α-γ, was normal. The ability of C8α-γ to promote the assembly of TCC in the presence of a limited amount of C8β or in the apparent absence of this subunit was confirmed using purified components, by mixing C5b6 and either of the purified C8 subunits together with C7 and C9. These data show that soluble TCC can be formed in C8β-deficient sera that contain little or no C8β.
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