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Subgroup classification of feline leukemia and sarcoma viruses by viral interference and neutralization tests

Abstract Diverse strains of naturally occurring feline leukemia and sarcoma viruses share the species-specific group specific antigen (gs-1), but reveal similarities and differences between individual members of the group with respect to viral envelope antigens. Such antigens can be demonstrated by viral interference and viral neutralization tests. The occurrence of three envelope antigens enabled us to classify the feline type C viruses into three subgroups of A, B and C. The property of initial viral infectivity (viral attachment and penetration into cells) and the induction of type-specific virus neutralizing antibodies appear to be controlled by the same envelope antigen. Thus, the replication of a feline leukemia virus in feline embryo cell cultures was accompanied by the development in these cultures of a viral resistance to the cell-transforming effects of antigenically related but not unrelated feline sarcoma viruses and feline leukemia pseudotypes of murine sarcoma virus. The presently known naturally occurring feline leukemia and sarcoma viruses of B and C subgroups were found to be antigenic mixtures containing an A subgroup virus as one of the components. These studies suggest that feline type C viruses may gain entry into cells at cell receptor sites specific for each major envelope antigen.

Viral interference in feline leukemia-sarcoma complex

Feline leukemia viruses replicate in feline embryo fibroblast cultures without causing visible effects. The virus-infected cultures acquire a resistance to superinfection with the closely related focus-forming feline leukemia pseudotypes of murine sarcoma virus and the feline sarcoma viruses. This induction of viral interference in tissue cultures with the cell-transforming effects of the challenge viruses can be used as a quantitative in vitro assay for the detection of feline leukemia viruses. Preliminary observations indicate that the interference is virus strain-specific (type-specific) and suggest the existence of distinct differences in viral envelope characteristics demonstrable in the viral interference tests.

Differential host range of viruses of feline leukemia-sarcoma complex

Abstract Selected strains of feline leukemia and sarcoma viruses of subgroups A, B, and C show a differential pattern in their ability to cross species barrier and productively infect cells of heterologous host species. A virus of subgroup B showed the widest host range; it caused productive infection of cells of diverse host species including cells from cat, human, monkey, dog, bovine, pig, and hamster species. Two virus strains of subgroup A showed the narrowest host range; of the cells of several mammalian species examined, they only caused productive infection of cat and dog cells. Preliminary studies indicated that certain other strains of subgroup A viruses cause productive infection of whole human embryo cells. One strain of subgroup C virus examined showed a host range that was intermediate between that of A and B subgroup viruses. This strain caused productive infection of cat, dog, and certain human cells. In addition, the subgroup C virus caused productive infection of guinea pig cells found to be resistant to subgroup A as well as subgroup B virus strains examined. Preliminary studies suggested that certain, but not all, virus mixtures of A and B viruses can be purified into B type by passage of virus in heterologous human cells. The factor(s) that may govern the differential susceptibilities of heterologous host cells to the described strains of feline viruses are discussed.

ST feline sarcoma virus. Biological characteristics and in vitro propagation.

Summary The biological properties and in vitro growth behavior of the Snyder-Theilen strain of feline sarcoma virus (ST-FSV) were determined. The virus replicated and induced cell transformation in feline embryo fibroblast cultures as well as in heterologous host cultures of human, canine, and porcine origin. Virus stocks were found to contain an excess of an associated, noncytopathogenic virus identical with the feline leukemia virus. Focus assays in feline embryo cultures gave “nondefective” “one-hit” titration patterns. The viral envelope characteristics established by viral neutralization and viral interference tests indicated that the ST-FSV is similar or identical with the Gardner-Arnstein strain of feline sarcoma virus and is a member of the subgroup B of the feline leukemia-sarcoma viruses.

Characterization of Xenotropic and Dual-tropic Type C Retroviruses Isolated from Abelson Tumour

Tumours induced in Balb/c mice by Abelson virus complex were found to contain a xenotropic virus (A-X-MuLV) and an NB-tropic, dual-tropic virus (NBX), in addition to the Moloney leukaemia virus (M-MuLV) and the defective, transforming Abelson virus genome. Both A-X-MuLV and NBX virus were presumably present in a genomically masked form and could be recovered only by co-cultivation of tumour cells with permissive cells. Only about 0.87% and 0.13% of the viruses in the co-culture supernatant represented A-X-MuLV and NBX virus respectively; the majority were M-MuLV. The NBX virus acted more efficiently than the HIX virus (Fischinger et al., 1975) as helper to rescue murine sarcoma virus (MSV) from S+L-cells of hamster, rat and mouse origin, whereas the converse was true for those of cat and human origin. The interference and nuetralization patterns suggested that the NBX virus was an env gene recombinant between A-X-MuLV and M-MuLV. The fact that NBX virus cross-reacted in radioimmunoassays with gp70s of both M-MuLV and Balb: virus-2 provides evidence for the recombinant nature of the NBX gp 70-coding gene which was probably derived from both M-MuLV and a virus similar to Balb: virus-2 or A-X-MuLV. The presence of a unique antigenic determinant on the gp70 of NBX virus is also suggested. Both A-X-MuLV and NBX virus cross-reacted with type-specific p12s of M-MuLV and Balb: virus 2- suggesting that the gag gene coding for p12 of NBX virus was derived from the A-X-MuLV, which was itself a recombinant, its p12-coding gene being derived from both Balb: virus-2-like virus and M-MuLV. The NBX virus was not oncogenic when tested in newborn Balb/c mice.

Enzyme immunoassay for feline oncornavirus-associated cell membrane antigen (FOCMA) and detection of FOCMA in cell extract by enzyme immunoassay inhibition test

An enzyme immunoassay (EIA) for FOCMA has been developed. The assay uses alkaline phosphatase-conjugated rabbit anti-cat IgG as the second antibody and p-nitrophenyl phosphate as the substrate for the enzyme to detect cat FOCMA antibody bound to the target cells. In comparison with the indirect immunofluorescence (IIF) test, which was originally used for FOCMA assay, our results showed a good correlation between the two methods. The EIA gives a more objective measure of FOCMA reactivity than does IIF. FOCMA was successfully extracted from FOCMA-positive cell membranes by 0.5% Triton X-100 and further fractionated by ammonium sulfate. The FOCMA activity was assayed by IIF and EIA inhibition test. Most of the FOCMA activity was found in the fractions precipitated by 30% and 50% ammonium sulfate saturation.

Production of antibodies against feline leukemia and sarcoma viruses and the feline oncovirus-associated cell membrane antigen in strain 2 guinea pigs

Abstract Cloned cell lines of guinea pig tumor induced by the Snyder-Theilen strain of feline sarcoma virus with feline leukemia virus subgroup C as helper, ST-FeSV (FeLV-C), have been established. The cell line releases high titers of ST-FeSV (FeLV-C) (10 3 −10 4 FFU/0.2 ml) and 1 log excess of FeLV-C. In vivo studies of one of the cell lines, GPTC C1 1 , showed that as little as 100 cells could induce tumors in weanling guinea pigs. The tumors progressively grew and eventually killed the animals within 23 days. Sera from guinea pigs carrying tumors contain antibodies to FeLV group-specific antigen, FeLV-C virus envelope antigen, and feline oncovirus-associated cell membrane antigen (FOCMA). The three groups of antibodies seem to be distinct as demonstrated in the absorption tests with appropriate antigens.