Padman S. Sarma

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.

An avian leucosis group-specific complement fixation reaction. Application for the detection and assay of non-cytopathogenic leucosis viruses

Abstract Sera of hamsters bearing large primary or transplanted subcutaneous fibrosarcomas induced by the Schmidt-Ruppin (S-R) strain of Rous sarcoma virus contain complement-fixing (CF) antibodies reactive not only with the homologous virus, but also with antigens of other avian leucosis viruses. Using this group-specific reaction, a complement fixation test (the COFAL test) was developed for the specific detection and assay of viruses of the avian leucosis group; the test appears to be at least as sensitive and useful as the resistance-inducing factor (RIF) interference procedure. Virus was assayed by inoculating decimal dilutions of virus into chicken embryo fibroblast cultures grown in petri dishes or in roller tubes and testing the inoculated cultures for the development of CF viral antigens. End points for virus assays were obtained in petri dish cultures after one or two cell transfers and also in roller tube cultures without cell transfers. In both systems, virus diluted 10−4 to 10−5 was detected within 10 days of virus inoculation and final titration end points were often reached within 2 weeks. Rous-associated virus (RAV) was readily demonstrated in the Bryan strain but not in the S-R strain of Rous sarcoma virus. The test was effective in demonstrating naturally occurring avian lymphomatosis virus.

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.

Feline Leukemia and Sarcoma Viruses: Susceptibility of Human Cells to Infection

Human embryonic cells are highly susceptible to infection with feline leukemia and sarcoma viruses. These viruses were propagated in human cultures without antigenic modification or loss of infectivity for cat or human cells. Virus stocks contained at least 106 infectious units of virus per milliliter for human cells. Virus present in 10-6 dilution of virus stock replicated to detectable amounts as early as 7 days after virus infection. The feline sarcoma virus induced morphological transformation of human cells.

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.

Complement-fixation test for feline leukemia and sarcoma viruses (the COCAL test)

Abstract A feline leukemia and sarcoma group-specific complement-fixation (CF) test has been developed, analogous to the COFAL test for the avian leukosis viruses and the COMUL test for the murine leukemia viruses. CF viral antibodies used in this test were prepared by immunizing rabbits with ether-disrupted feline leukemia virus and by the induction of fibrosarcoma in beagle dogs with the GA strain of the feline fibrosarcoma virus. The dog CF antibodies contained viral envelope antibodies as well as antibodies to the ether-resistant, nonsedimentable antigens (gs antigen) of the virus. A tissue culture CF viral antigen induction test was devised for the detection and assay of infectious virus and viral-neutralizing antibodies. The test was useful and sensitive for the routine detection and assay of various field strains of feline leukemia virus. High titers of infectious virus and/or viral antigen were found in various preparations from cats with lymphosarcoma and cultures of feline, canine, and human cells inoculated with the virus. The presence in feline sarcoma virus stocks of 100- to 1000-fold excess of noncytopathogenic feline leukemia virus was detected. The CF test for feline leukemia and sarcoma viruses (the COCAL test), may be useful as a routine laboratory tool in the studies of the natural occurrence and transmission of feline leukemia and sarcoma viruses in cats and other species.

A Simplified Tissue Culture Tube Neutralization Test for Rous Sarcoma Virus Antibodies

Summary A simplified tube neutralization test for assay of antibodies to Rous sarcoma virus and related avian leucosis viruses was described which appears to be suitable for differentiating serotypes and for surveys for naturally occurring antibodies against these viruses. The test was used in preliminary surveys for antibodies to Rous virus in sera of various species. Most hens in 3 commercial flocks of laying chickens were found to be positive for antibody. One of 3 hens without detectable antibodies was found to have RIF viremia. No antibodies were found in limited numbers of sera from turkeys, Japanese quail, pigeons or in sera from human subjects with or without leukemia.

A survey of cats and humans for prevalence of feline leukemia-sarcoma virus neutralizing serum antibodies.

Summary Sera of adult domestic cats and humans (veterinarians and laboratory workers) were surveyed for the presence of virus neutralizing antibodies against feline leukemia-sarcoma viruses of subgroups A, B and C. A focus neutralization test was used based on the neutralization of feline cell transforming effects of approximately 100 focus forming units of feline leukemia pseudotypes of Harvey strain of murine sarcoma virus (Harvey strain of murine sarcoma virus with the viral envelopes of the described serotypes of feline leukemia virus). Virus neutralizing envelope antibodies against one or more envelope antigenic types were found in the sera of 13 of 59 (22%) cats without neoplasia and in 9 of 38 (23.7%) cats with neoplastic disease but not in the sera of 36 veterinarians or in 33 laboratory personnel working in two laboratories engaged in feline leukemia virus research. The implications of these findings are discussed. We are indebted to Drs. Roger Wilsnack and Jack Gruber for providing the goat antiserum against FL-74 virus and to Dr. Paul Arnstein for providing the dog antiserum against GA strain of feline sarcoma virus.

The SM Strain of Feline Sarcoma Virus. Biologic and Antigenic Characterization of Virus

Summary The SM strain of feline sarcoma virus (SM-FSV) isolated by in vivo methods from a naturally occurring case of feline fibrosarcoma was characterized in vitro. The virus propagated and induced morphologic transformation of homologous feline host cells as well as heterologous host cells of human, canine and porcine origin. The virus propagated in feline cultures retained its oncogenic potential for newborn cats. The SM-FSV was found to contain an associated nontransforming feline C-type virus at a concentration of approximately ten fold higher level than the cell transforming virus. The sarcoma virus transformed feline cells with one-hit kinetics suggesting that this associated nontransforming virus is not required for the initiation of the cell transforming event. Viral interference tests and viral neutralization tests with type-specific antisera suggested that the SM-FSV consisted of a mixture of antigenic types of the feline leukemia-sarcoma virus subgroups A and B. Isolation of a A subgroup nontransforming virus from virus stocks of the nontransforming SM-FSV associated virus was achieved by virus cloning techniques.

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.