NATURAL ANTIBODIES IN SERA FROM HEALTHY HUMANS TO ANTIGENS ON SURFACES OF TYPE-C RNA VIRUSES AND CELLS FROM PRIMATES

Sera from healthy humans contained naturally occurring antibody against group- or subgroup-specific antigen on the envelope of the following type C viruses isolated from primates: gibbon ape leukemia virus, simian (woolly monkey) sarcoma virus, baboon endogenous type C virus and putative human type C viruses [HL23V isolated from blood cells of a patient with acute myelogenous leukemia (HL23) and HEL-12V from human embryonic diploid cells (CIH-32)]. Two sera also reacted with C57BL/6 mouse leukemia induced by Friend virus. These results were obtained by indirect immunoelectron microscopy [IIEM] with various virus-producing cells and by absorption tests using as targets gibbon lymphosarcoma cells that release gibbon ape leukemia virus. In a previous report, the presence of natural antibody in sera from healthy gibbon apes was demonstrated. When the specificities of the human and gibbon natural antibodies were compared, the human natural antibody reacted with 2 nonproducing culture cell lines of human lymphocytic leukemia (CEM-A and MOLT) and with human embryonic diploid CIH-1(V-) cells [which became type C virus-producing CIH-32(V+) cells after many passages], but did not react with normal gibbon spleen monolayer cells. Gibbon natural antibody showed no reaction with CEM-A, MOLT and CIH-1(V-) cells but reacted with gibbon spleen monolayer cells. Neither human nor gibbon natural antibody that was reactive with gibbon ape leukemia virus crossreacted with feline leukemia virus and mouse wild-type AKR leukemia virus. The gibbon lymphosarcoma cells releasing gibbon ape leukemia virus were used in a screening study of sera from healthy humans. Of 72 sera screened by IIEM using this system, 55 were positive (76%); i.e., 26 of 35 males (74%) and 29 of 37 females (78%). The highest incidence of antibody production was in 1-10 yr olds and 31-40 yr olds, with the adults exhibiting higher levels. Differences in incidence of natural antibody were not sex-linked. Type C RNA viruses related to the gibbon ape leukemia virus, simian (woolly monkey) sarcoma virus family and the baboon endogenous type C virus family may be widespread in humans.