Complement‐mediated lysis of type‐C virus: Effect of primate and human sera on various retroviruses

Antibody‐independent complement‐mediated lysis of type‐C RNA tumor viruses (retroviruses) was measured in the sera of humans and other primates using the reverse transcriptase release assay. In this assay, preincubated mixtures of test serum and virus are assayed for the presence of viral reverse transcriptase released from disrupted virions. Serum decomplemented by heating possesses no such activity. Sera containing non‐specific heat‐labile factors inhibitory to the reverse transcriptase release assay are excluded from consideration. According to this assay, both normal and leukemic human sera, as well as sera from several other primate species including apes, Old World monkeys and New World monkeys, are all capable of lysing both endogenous and infectious primate and murine type‐C viruses. At least two non‐primate species (cat and rabbit) also possess this activity, although several other non‐primates do not. There is no appreciable viral specificity; each test serum possessing complement‐mediated virolytic activity can lyse all classes of retroviruses against which it is tested. Those primate species which spontaneously release retroviruses (baboon, squirrel monkey), as well as those primate species which are infected with exogenous retroviruses (rhesus, gibbon ape), are all capable of lysing their respective viruses. In addition, the relative efficiency of complement‐mediated viral lysis correlates better with primate phylogeny than with the relative ease of type‐C virus release or transmission. This would seem to suggest that complement‐mediated viral lysis does not, in fact, play a primary role in blocking the release or transmission of type‐C viruses among primates.