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 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 two 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. In contrast, 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. Out of 72 sera screened by indirect immunoelectron microscopy using this system, 55 were positive (76%), i.e., 26 out of 35 males (74%) and 29 out of 37 females (78%). The highest incidence of antibody production was in 1- to 10-year-olds and 31- to 40-year-olds, with the adults exhibiting higher levels. Differences in incidence of natural antibody were not found to be sex-linked. These findings suggest that type C RNA viruses related to the gibbon ape leukemia virus and simian (woolly monkey) sarcoma virus family as well as the baboon endogenous type C virus family may be widespread in humans.

Streptococcus pyogenes preparation OK-432: immunoprophylactic and immunotherapeutic effects on the incidence of spontaneous leukemia in AKR mice.

An inactivated and lyophilized preparation of a low virulence strain (Su) of Streptococcus pyogenes (group A) was designated OK-432. When 2- and 5-month-old AKR mice were inoculated im with OK-432 twice weekly throughout their life-spans, spontaneous leukemias occurred later and at a lower incidence than in control groups. By virus neutralization and cytotoxicity tests and by immunoelectron microscopy, antibodies against virus and cell-surface antigens of transplanted AKR leukemia were not detectable in sera of nonleukemic mice of any group. Whereas sera from mice treated with OK-432 were the only positive for interferon, viremia was clearly demonstrated in control groups by reverse transcriptase assays of the plasma.

Specificity of naturally occurring antibody in normal gibbon serum.

Gibbon natural antibody examined by immunoelectron microscopy reacted with the entire envelope of type C virus and with areas on the cell surface equivalent to or smaller than the diameter of a virion in gibbon and human culture cells infected with or releasing type C viruses. The antibody activity was absorbed completely by two cell cultures infected with gibbon ape leukemia virus and by the virus itself, and partially by normal gibbon spleen cells and dog thymus-derived cells infected with baboon endogenous type C virus, and fresh white blood cells obtained from a patient with chronic myelogenous leukemia in acute blastic crisis.

Cell-mediated immunity to Friend virus-induced leukemia. II. Characteristics of primary cell-mediated cytotoxic response.

The primary cell-mediated cytotoxic response to a Friend virus-induced leukemia, FBL-3, in C57BL/6 mice was measured by the 125IUdR release assay. Intraperitoneal (i.p.) inoculation of 1 x 10(1) FBL-3 cells produced progressive tumor growth (progressors); subcutaneous (s.c.) inoculation of as many as 5 x 10(6) FBL-3 cells produced only transient tumor growth (regressors), and these mice would subsequently resist i.p. challenge of FBL-3 cells at 3 days after s.c. inoculation. The kinetics of the primary cell-mediated cytotoxic response of regressors was biphasic. Significant cytotoxicity could be detected at 3 to 5 days after s.c. inoculation of 5 x 10(6) FBL-3 cells peaked at days 10 to 14, declined to a very low level or became undetectable around days 20 to 30; then the reactivity reappeared and persisted at least up to 60 days. In progressors, the kinetics of the cell-mediated cytotoxic response was similar to the regressors, but the reactivity was much lower. The cytotoxic response was found to be T cell dependent, during both the first peak (days 10 to 14) and the second peak (days 40 to 60). In adoptive transfer experiments, lymphocytes from regressors gave 90% protection against i.p. challenge of FBL-3; lymphocytes from progressors only gave 40% protection.

Cell-mediated immunity to Friend virus-induced leukemia. I. Modification of 125IUdR release cytotoxicity assay for use with suspension target cells.

Cell-mediated cytotoxic reactivity of C57BL/6 mice against syngeneic FBL-3 cells, a Friend virus-induced leukemia, was measured by the 125IUdR release assay with tumor target cells in suspension. The tests could be performed either with Linbro tissue culture plates(16-mm wells) or with Microtest II plates (6-mm wells). The former could only be harvested manually; the latter could be harvested mechanically by an automatic harvesting apparatus which permitted larger scale tests. With either plate, it was found that careful preparation of the target cells and of the attacker cells has important effects on the results obtained. When performed under optimal test conditions, the 125IUdR assay can be used as a very simple, objective, and reproducible assay for testing cell-mediated cytotoxicity.