Occupational exposure assessment using antibody levels: exposure to avian leukosis/sarcoma viruses in the poultry industry

Avian leukosis/sarcoma viruses (ALSV) infect and cause cancers in chickens. Poultry workers are exposed to ALSV and other infectious agents in the workplace. This study examines if industrial hygiene assessment of antibody levels in poultry workers can identify risky job tasks at the higher exposure risk to an infectious agent, i.e., ALSV. We compared ALSV antibody levels in poultry workers and control subjects. Occupational and demographical factors were examined for an association with the exposure risk in poultry workers. We found that the antibody levels were significantly higher in poultry workers than in control subjects. Job category and age together were significantly associated with the antibody levels in workers. Certain job tasks were identified with significantly higher antibody levels as compared to others, implying that recommendations should be made to protect workers at these jobs. The findings of this study indicate that the measurement of antibody levels in workers can be useful for industrial hygiene assessment of exposure to infectious agents.

Occupational exposure to poultry and prevalence of antibodies against Marek's disease virus and avian leukosis retroviruses

OBJECTIVES

To compare the prevalence of antibodies against Marek's disease herpes virus (MDV) and against avian leukosis viruses type C (ALV) in groups of workers exposed to poultry and in unexposed groups.

METHODS

Antibodies directed against avian viral proteins were detected by enzyme linked immunosorbent assay in 549 subjects. Exposure to chickens was high in two subgroups: farmers on intensive chicken farms and workers at chicken slaughterhouses. One subgroup, traditional farmers on dairy or pig farms with poultry, had moderate exposure to poultry. Another subgroup, farmers and slaughterhouse workers on quail farms, had high exposure to quails. Three subgroups were not exposed to chickens: farmers on dairy or pig farms without poultry, workers at cattle slaughterhouses, and white collar workers. Also, MDV antibodies were tested after serum sample adsorption with chicken antigens in 134 serum samples.

RESULTS

The prevalence of antibodies against MDV was significantly higher in the exposed subgroups than in unexposed groups (odds ratio (OR) 6.17; 95% confidence interval (95% CI) 3.91-9.75). No association was found between seroprevalence and age. However, higher prevalence was found among women and was related to duration of exposure to chickens. The concentration of antibodies from a few subjects remained very high after adsorption. Significant differences between the men and women were found for the prevalence of antibodies for ALV but were not related to exposure to chickens.

CONCLUSIONS

The prevalence of antibodies against MDV was significantly higher among workers exposed to chickens and was related to sex and duration of exposure. The higher prevalence of antibodies against avian oncogenic viruses found among women compared with men may be induced by differences in exposure or by genetic factors. The meaning of these high titres could be related to the presence of MDV in humans. Because the involvement of animal oncogenic viruses in human cancer is indicated by epidemiological and some experimental studies, the integration of viral DNA in human cells needs to be investigated.

Variable response to a candidate cancer vaccine antigen: MHC control of the antibody response in the rat to avian erythroblastosis virus (AEV)-encoded epithelial growth factor receptor but not AEV-encoded thyroid hormones receptor

BACKGROUND

A problem likely to be encountered in any cancer immunotherapy based on vaccination with a single protein or peptide is variation in the host response. A particularly informative example is provided by the two oncogenic proteins, one intracellular and the other extracellular, encoded by the avian erythroblastosis virus (AEV), homologs of the thyroid hormones receptor (THsR) and the epithelial growth factor receptor (EGFR), respectively.

MATERIALS AND METHODS

Antibodies to these two proteins were assayed by radioimmune precipitation (RIP) in sera from MHC-congenic rats immunized by virally induced tumors.

RESULTS

Among the four haplotypes tested, RT1(1) rats exhibited a significantly lower response to the EGFR homolog than the high responders RT1c and RT1u, while RT1a rat strains had an intermediate response. Analysis of the recombinant haplotype RT1ac indicated that the response is controlled, as expected, by the class II locus of the MHC. In contrast, these rat strains responded uniformly to the intracellular THsR homolog.

CONCLUSIONS

These results support the hypothesis that MHC restriction of the response to self-related proteins reflects mainly a tolerance mechanism. They sound a note of warning for cancer vaccine development, and also one of positive advice. The likelihood of MHC restriction suggests that a widely applicable polyvalent vaccine should be the final aim in cancer immunotherapy. Yet, paradoxically, evidence of MHC restriction can help establish that a candidate vaccine is likely to prove effective.

Reflections on the pathogenesis of diseases caused by the acute avian leukosis/sarcoma viruses with special reference to avian erythroblastosis

The various diseases that follow experimental infection with the acute and non-acute avian oncoviruses are discussed with special reference to the pathogenesis of avian erythroblastosis. One view, based on in vitro studies, sees erythroblastosis as the product of a failure in the differentiation of virus-infected stem cells to mature erythrocytes, as a result of cell 'transformation'. The results of some in vivo studies, however, point to a resemblance of the disease to a haemolytic anaemia, where cellular death is an important component. It seems probable that the disease is the result of transformation of cells of the erythroblastic series followed by the death of many of these cells due to influences that have not yet been determined. Determination of the causes of this cellular death may prove to be as important for our understanding of the problem of leukaemia as the work that has already been accomplished in explaining the causes of cell transformation. It is also suggested that the tendency of gs amino acid sequences of the avian leukosis viruses and mouse leukaemia viruses to form fusion proteins with a variety of proto-oncogenes may be part of a wider phenomenon, and that these sequences may fuse with other proteins, altering their properties. More work is required on the possibility that there is an undiscovered immunological component in the progression of the L/S diseases.

The major histocompatibility complex of chickens controls the infection of early chicken embryos by MC29 virus

Embryos from isogeneic chicken lines belonging to different haplotypes and known to be resistant to infection by avian retroviruses of subgroups A and E were infected on the 3rd (E3) and 5th day (E5) of incubation with MC29 virus (MC29-RAV-1 pseudotype; A subgroup-derived envelope). Despite the trait for resistance, E3 embryos developed the specific heart tumors previously described in outbred E3 embryos. The CB line (B12/B12, C/AE) was more susceptible than the congenic line CC (B4/B4, C/AE). In both lines, the heart was the unique target at E3 for MC29. No tumors of the heart or other organs appeared upon infection at E5 or E10. In the A subgroup susceptible line 6 (B2/B2, C/E) both heart (50%) and skin (100%) were transformed upon E3 infection. Hybrids of line 6 with the CB line expressed skin (100%) and heart (95.4%) tumors. On the other hand, the 6 x CC combination revealed 96.7% of skin tumors while heart tumors occurred only in 1 of 31 embryos (3.2%). To distinguish the respective influences of the MHC and of the tv-a allele, crosses with the la line (B7/B7, C/O) were carried out and tested with MC29. The findings indicate that resistance of the embryos to MC29 heart tumors is associated with the B4/B4 haplotype, supporting the interpretation that the MHC has a role in MC29 cell tropism and v-myc expression. The target cells in tumors were determined by immunofluorescence staining. Cells infected in the heart belonged to the myogenic lineage, as expected from previous studies. In skin anomalies the epidermal cells were double-stained with anticytokeratin and anti-env antibodies, many cells in the dermis also reacted with anti env antibodies.

Poultry oncogenic retroviruses and humans

Viruses of the avian leukosis/sarcoma group (ALSV) and reticuloendotheliosis viruses (REV) are highly prevalent in chickens and turkeys and naturally cause tumors in them. Commercial chickens are positive for antibodies, and a proportion actually carry infectious virus. Virus may be present in chicken products and in eggs, thus human exposure is virtually universal. The viruses show little potential for producing infectious viral particles in mammalian cells; nevertheless, they have the capacity to infect and transform mammalian cells (including human cells) in vitro, and to induce tumors in a variety of mammals, including primates. Most, but not all, of the serological studies in humans have been negative. Given the known behavior of these viruses in mammals, this was not unexpected. Moreover, there were methodological problems with most of the studies. There is some epidemiological evidence associating putative poultry exposure with cancer in humans. However, this has not been rigorously investigated. This paper is a comprehensive review of the extent of the carcinogenic potential these viruses show for humans. It is concluded, virological evidence indicates, that these viruses could conceivably have a carcinogenic potential for humans, but if so, at a level much less than in chickens. Whether this is insignificant, or translates to a real risk, is not known at the moment. Therefore, there is a need for definitive studies to completely rule out this possibility.

Susceptibility of thymocytes for infection by chicken anemia virus is related to pre- and posthatching development

To investigate the age-dependent mechanism of susceptibility for chicken anemia virus (CAV) infection, we inoculated embryos and chickens of ages between day 9 of embryonic development and day 28 after hatching with CAV. Chicken embryos inoculated at days 9 and 11 of development showed no CAV-infected cells in the thymus, nor in other lymphoid organs. Many CAV-infected cells were detected in the thymic cortex of all chicken embryos inoculated at days 13 and 16 of development and of all chickens inoculated 1, 3, and 7 days after hatching. All embryos and chickens that contained CAV-infected cells in the thymus also contained CAV-infected cells in the bone marrow, but not in the bursa of Fabricius or the spleen. In chickens inoculated at days 14 and 21, only few CAV-infected cells were detected in the thymus, whereas these cells were not detected in thymi of 28-day-old inoculated chickens. Depletion of the thymic cortex was only detected in chickens inoculated from day 16 of embryonic development till day 21 after hatching. Only hematocrit values of the chickens inoculated 1 and 3 days after hatching were below normal. The rationale for the simultaneous susceptibility of cells of the T-cell lineage and cells of the erythrocyte lineage is discussed. As far as the thymus is concerned, the absence of clinical and microscopical signs of CAV infection in older chickens and the inability of CAV to infect embryos at days 9 and 11 of embryonic development may be caused by a lack of susceptible thymocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Immune response and resistance to Rous sarcoma virus challenge of chickens immunized with cell-associated glycoproteins provided with a recombinant avian leukosis virus

The Rous-associated virus 1 env gene, which encodes the envelope gp85 and gp37 glycoproteins, was isolated and inserted in place of the v-erbB oncogene into an avian erythroblastosis virus-based vector, carrying the neo resistance gene substituted for the v-erbA oncogene, to generate the pNEA recombinant vector. A helper-free virus stock of the pNEA vector was produced on an avian transcomplementing cell line and used to infect primary chicken embryo fibroblasts (CEFs) or quail QT6 cells. These infected cells, selected with G418 (CEF/NEA and QT6/NEA, respectively) were found to be resistant to superinfections with subgroup A retroviruses. The CEF/NEA preparations were used as a cell-associated antigen to inoculate adult chickens by the intravenous route compared with direct inoculations of NEA recombinant helper-free virus used as a cell-free antigen. Chickens injected with the cell-associated antigen (CEF/NEA) exhibited an immune response demonstrated by induction of high titers of neutralizing antibodies and were found to be protected against tumor production after Rous sarcoma virus A challenge. Conversely, no immune response and no protection against Rous sarcoma virus A challenge were observed in chickens directly inoculated with cell-free NEA recombinant virus or in sham-inoculated chickens.

RRR-alpha-tocopheryl succinate enhances T cell mitogen-induced proliferation and reduces suppressor activity in spleen cells derived from AEV-infected chickens

RRR-alpha-tocopheryl succinate was demonstrated to be a potent in vitro modulator of retrovirus-induced immune abnormalities. Spleen cells from avian erythroblastosis virus (AEV)-infected chickens exhibit suppressed T cell mitogen-induced proliferative responses and elevated levels of suppressor T cell activity. In vitro addition of RRR-alpha-tocopheryl succinate resulted in amelioration of these abnormalities. Antioxidants including Trolox (a water-soluble analogue of RRR-alpha-tocopherol with antioxidant properties) and a combination of butylated hydroxyanisole and butylated hydroxytoluene were able to restore immune functions to levels similar to those achieved with RRR-alpha-tocopheryl succinate treatment. Aspirin, an irreversible inhibitor of cyclooxygenase activity, was capable of ameliorating some of the AEV-induced immune dysfunctions. These studies suggest a role for the antioxidant functions of RRR-alpha-tocopheryl succinate in modulation of retrovirus-induced immune abnormalities.

Identification of two additional v-sea-encoded proteins in avian erythroblastosis virus, S13-infected fibroblasts

Rabbit antibodies prepared against a v-sea-encoded polypeptide expressed in bacteria were used to characterize the v-sea-encoded proteins in cells transformed by the avian erythroblastosis virus, S13. In addition to the two previously described v-sea-encoded proteins, gp155 and gp70, two additional proteins were identified of molecular weights 38,000 and 36,000 Da. Interestingly, these two proteins were found only in fibroblasts infected with the S13 virus and not in S13-transformed erythroid cells. These two proteins were phosphoproteins, but, unlike the two previously characterized v-sea-encoded proteins, they did not appear to be modified by the addition of N-linked sugars. Possible mechanisms for the biosynthesis of these two new proteins are discussed.

Immunoblotting with polyclonal and monoclonal antibody to avian myeloblastosis protein p27: studies of liver proteins in chickens with erythroblastosis

An antigen detected by complement fixation with polyclonal antibody to avian myeloblastosis virus (AMV) antigen p27, appears in the livers of chickens inoculated with avian erythroblastosis virus (AEV). It can be demonstrated at the 30,000 dalton (30K) molecular weight level by Western immunoblotting of electropherograms of AEV infected liver extracts. The 30K protein reacted strongly with this polyclonal antibody but only weakly with a monoclonal antibody to the same viral antigen and possible explanations for this have been suggested. Both antibodies also appeared to react with other than viral components in the preparations of AMV used. As this apparent non-specific attachment of highly specific antibody may have as its explanation the failure of the gelatin to prevent nonimmunologically determined binding of the immunoglobulin; other blocking agents should be investigated.

Immune response to avian leukosis virus determined by the cell-mediated focus-reduction (CEMFOR) assay

A cell-mediated focus-reduction (CEMFOR) assay was used to determine the sequential development of cell-mediated immunity to avian oncornaviruses and the nature of the cells participating in this immune reaction. Peripheral blood leukocytes of Leghorn chickens that had regressed Rous sarcoma virus-induced tumors or were immune to avian leukosis virus had CEMFOR activity. The response was biphasic early in the infection. Peripheral blood leukocytes from nonimmune chickens or viremic, immunologically tolerant chickens did not have CEMFOR activity. Sera from leukosis virus-immune chickens blocked CEMFOR activity. The early CEMFOR response was mediated by T-cells. The late response was mediated by an adherent cell population possibly augmented by the presence of T-cells.

Observations on an enzyme-linked immunosorbent assay for the detection of antibodies against avian leukosis-sarcoma viruses

In the detection of antibodies against exogenous subgroup A avian leukosis viruses (ALVs) using a representative subgroup A virus, concordance between enzyme-linked immunosorbent assays (ELISAs) and serum neutralizations ranged from 83 to 95%. In ELISAs, subgroup A- and subgroup B-specific neutralizing antisera were equally reactive against ALVs of subgroups A, B, and E. Conversely, little cross-reactivity of high-titered subgroup E antisera was observed against subgroup A viruses. Significant cross-reactivities of spontaneously induced subgroup E-neutralizing antisera were observed when tested against a representative subgroup B ALV. Because some normal chickens spontaneously mount antibodies against infectious endogenous viruses, misleading results may be obtained if subgroup B or E ALVs are the source of target antigens in ELISAs.

Monoclonal antibodies specific for the virion polypeptide, p27, of avian retroviruses

The major component of the core structure of avian sarcoma leukosis viruses is a 27 kD molecular weight polypeptide, p27. Spleen cells from mice immunized with the Schmidt-Ruppin strain of Rous sarcoma virus (RSV) were fused with mouse myeloma cells (SP2/0), and hybridoma cell lines producing monoclonal antibodies to p27 were isolated. The monoclonal antibodies were all of the IgG1 subclass with kappa light chains. These antibodies immunoprecipitated p27 and its precursor proteins from extracts of RSV-transformed cells. Reciprocal competitive binding experiments defined five nonoverlapping antigenic determinants within p27. The monoclonal antibodies also immunoprecipitated the transforming protein, p110gag-myc, from avian myelocytomatosis virus transformed cells. Their usefulness in studies of virion maturation and viral oncogenesis is discussed.

Chicken fetal and adult antigen expression on erythroleukemia cells before and after induced differentiation

Avian erythroblastosis virus strain R (AEV)-transformed, cloned erythroleukemia cells from three different ages of SC strain chickens were analyzed before and after differentiation induced by 1.0 mM butyric acid for expression of chicken fetal antigens (CFAs) and chicken adult antigens (CAAs) and for hemoglobin expression. Immunofluorescent analyses show the loss of individual CFA determinants from erythroleukemia cells with induced differentiation, although there appeared to be no correlation between CFA loss and onset of hemoglobin production. Erythroleukemia cells were examined by cell surface labeling followed by immunoprecipitation with antisera specific to CFAs and CAAs. Erythroleukemia cells expressed CFAs and CAAs on their membranes that are not reported to be expressed by the target cell of AEV. The expression of CAAs and the enhanced expression of CFAs by erythroleukemia cells may be due to limited cellular differentiation, alterations in regulatory controls of genes coding for CFAs and CAAs, or increased levels of production of previously undetected CFAs and CAAs following AEV transformation. Control and induced erythroleukemia cells expressed CFAs and CAAs that differed both quantitatively and qualitatively from normal erythroid cells. Molecular weight variations of CFAs and CAAs observed in the erythroleukemia cells may represent glycolyzation differences between AEV-transformed cells and normal erythroid cells.

Effects of dexamethasone on antigen expression and virus production in avian sarcoma virus-transformed cells

We studied the effects of dexamethasone on virus production and antigen expression in avian retrovirus-infected chick embryo fibroblast (CEF) cells. The presence of specific receptors for this hormone in both normal and infected CEF cells could only be demonstrated using cultures that were at or near confluence. Dexamethasone, while not toxic to the cells, exerted a growth-retarding influence when employed at concentrations of 10(−8) or 10(−9) M. These same concentrations of hormone were inhibitory to virus production, elaboration of plasminogen activator activity, and antigen expression as determined in a sensitized lymphocyte stimulation assay. In contrast, infected cells that had been treated with hormone displayed enhanced reactivity in a specific immunofluorescence test.

Characterization of an antigen associated with the Marek's disease lymphoblastoid cell line MSB-1

A Marek's disease lymphoblastoid cell line (MSB-1) has been analysed by immunoprecipitation for expression of tumour-associated antigen, Marek's disease virus (MDV)-specific antigens and antigens specific to avian leukosis-sarcoma viruses. Rabbit antisera raised against two independently derived cell lines after extensive absorption with normal chick cells reacted with a polypeptide of mol. wt. 40 000 (40K) in extracts of MSB-1 cells. The 40K polypeptide was not present in myeloblasts or in chick embryo fibroblasts (CEF) infected with MDV and did not react with antiserum raised against normal chicken thymus antigens. The possibility that the 40K polypeptide is a tumour-associated antigen is discussed. Seven MDV-specific antigens were noted in infected CEF (mol. wt. 110K, 100K, 80K, 70K, 50K, 35K and 32K) but none of these was detected in MSB-1 cells. The avian leukosis-sarcoma group-specific antigen P27gag and its precursor Pr76gag were not found in MSB-1 cells, confirming that expression of mature gag protein is not required for transformation by MDV. However, two polypeptides of unknown origin and function (mol. wt. 180K and 110K) were precipitated from MSB-1 cells with a rabbit anti-Rous sarcoma (Schmidt-Rupin, subgroup D) antiserum.

Immune stimulation of sensitized chicken lymphocytes by avian retrovirus proteins

Peripheral blood lymphocytes of chickens bearing tumours induced by avian sarcoma virus can be specifically stimulated to divide by the crude culture fluids of virus-infected cells. In this communication, we show that relevant antigenic activity apparently resides in each of the internal virus proteins p15 and p27. The ability of infectious culture fluids to be mitogenic for sensitized lymphocytes is greatly reduced following treatment with antibodies specific for either total avian myeloblastosis virus (AMV) protein or for p27.

A "liver" antigen associated with avian erythroblastosis: binding by bentonite and precipitation with sodium dodecyl sulphate

The properties of a complement fixing antigen, EbAg, extracted from erythroblastosis-affected chicken livers are described. The antigen in extracts freed of structural protein is strongly bound by bentonite, but not by barium sulphate. Strongly alkaline solutions of sodium dodecyl sulphate are required to release the antigen from bentonite. Acidification of the detergent solution precipitates the active solution precipitates the active protein. Extraction of heme from the acidified detergent precipitate by methyl-ethyl ketone further purifies the antigen. This acid detergent treatment eliminates the need to use bentonite as a purification step.

Establishment of infection by spleen necrosis virus: inhibition in stationary cells and the role of secondary infection

The relationship of two early events in the establishment of infection by avian retroviruses, the inhibition of viral DNA synthesis in stationary avian cells and the secondary infection which occurs after infection of replicating cells, was investigated. When neutralizing antibody to spleen necrosis virus was used to prevent secondary infection, the amount of unintegrated linear spleen necrosis virus DNA detected was much lower in infected stationary cells than in infected replicating cells. The amount of unintegrated linear spleen necrosis virus DNA in stationary cells was less than one copy per cell even at high multiplicities of infection. Viral DNA synthesis resumed after stimulation of the cells to replicate. The time of this viral DNA synthesis was closely correlated with renewed cellular DNA synthesis. In addition, blocking secondary infection of replicating cells prevented the rate of virus production from reaching the high levels usually associated with a normal productive infection by SNV. Virus production increased if secondary infection was allowed. However, this rise in virus production was not proportional to the amounts of viral DNA integrated after secondary infection.

Heterologous tumor growth patterns induced in related MHC-defined chicken lines by separate isolates of an avian sarcoma virus strain

Different patterns of tumour growth resulted from inoculation of separate isolates of the Subgroup C Bratislava 77 strain (B77) of Avian Sarcoma Virus (ASV) into three closely-related inbred lines of chickens. The major genetic difference between these chicken lines is that each is homozygous for a different MHC haplotype. Since for one of the viral isolates, resistance to progressive tumour growth has been shown to be controlled by MHC-linked genes, the data presented here suggest that MHC-controlled tumour rejection operates on viral or cellular determinants different from those which define classical viral group of subgroup specificity.

Isolation of monoclonal antibodies against avian oncornaviral protein p19

For the production of monoclonal antibodies against pp60src and the gag precursor protein Pr76gag, the spleens of mice bearing tumors that had been induced by avian sarcoma virus Schmidt-Ruppin D-transformed cells were used. One hybridoma culture produced antibodies that were directed against the p19 portion of the gag precursor. However, no antibodies directed against pp60src could be detected in any of the hybridoma supernatants. The anti-p19-producing hybridoma culture was cloned twice in soft agar, and a stable clone was used for the production of high-titer ascites fluid in mice. The monoclonal antibodies belonged to the immunoglobulin G subclass 2b. The antibodies precipitated Pr76gag and the processed virion-associated p19, as well as the 75,000-molecular-weight gag fusion protein from avian erythroblastosis virus-transformed bone marrow cells. Also, viral ribonucleoprotein complexes were specifically precipitable, indicating that they contain p19 molecules.

[Study of viral contamination of Japanese quail and cell cultures from their embryos]

Agents identified as adenovirus CELO were isolated from organ suspensions of 1500 Japanese quails (JQ) in 4 experiments. No contaminating viruses were found in examinations of cell cultures prepared from the kidneys of 80 JQ. Negative results were obtained in examinations of 163 antigens from JQ organs in the COFAL test. Agents identified as mycoplasma were isolated in 16 cases from 736 specimens of the virus-containing fluid used for manufacture of measles virus. According to the results of the CFT, 59 antigens prepared from Japanese quail embryo cell cultures contained no oncornavirus antigens and were negative in the COFAL test. Among 1848 JQ sera examined for the presence of antibody to leukemia-sarcoma complex viruses only 2 sera were found in 1976 to contain antibody to Rous sarcoma virus. No antibody to Marek disease virus in 414 serum samples or to Newcastle disease virus in 554 sera were detected. Among 500 sera tested 30.8% contained antibody to adenovirus CELO.

Antisera from mice and rats incubated with syngeneic Rous sarcoma cells

CDF1, (BALB/c X DBA/2)F1, mice were repeatedly inoculated with transplantable mouse Rous sarcoma (SR-CDF1) cells which were half-killed by 60Co-irradiation beforehand to attain prolonged immunization. The sera obtained from these mice contained antibodies against the src and gag gene products of Rous sarcoma virus (RSV). On the other hand, Fischer rats inoculated with syngeneic rat Rous cells transformed by Bryan high titer strain of RSV (BH(-)-3Y1) produced antibodies against the gag gene products but not the src gene product of RSV. As a substrate for the protein kinase associated with the src gene product, mouse IgG was found to be much less efficient than rabbit IgG when assayed in immunoprecipitates. Several other properties of the mouse antiserum were described.

A survey of non-specific cross-protective immunities induced by avian retroviruses

Reticuloendotheliosis virus strain T (REV-T) induced immunity in chicks to challenge by representative subgroup members of the avian leukosis-sarcoma virus (ALSV) complex. Immunity levels were compared to determine the extent of antigenic relation between REV-T and the ALSV complex. Reciprocal studies using ALSV subgroup members and pheasant viruses as immunogens and REV-T as challenge were also performed. It was concluded that reciprocity of immunity is not equal between the viruses studied, nor is immunity directly related to the virus-neutralizing-antibody levels induced by immunization with the viruses studied. In some cases, the levels of cross-protection demonstrated may be a sign of the induction of antibodies to common or similar tumor-specific surface antigens rather than complete antigenic identity between REV-T and the ALSV members used; in others, virus-neutralizing antibodies may be a sign of partial identity between some proteins of REV-T and ALSV subgroup members.

The immune response against the ASV-coded src-gene product in syngeneic mice

The antigenicity of the avian sarcoma virus (ASV)-coded src-gene product pp60src, which is responsible for fibroblast transformation after ASV infection, has been investigated in STU mouse fibrosarcoma cell lines and the corresponding immune response in syngeneic mice has been determined. The development of effective anti-pp60src antibody titres depends on the mode and stie of injection of tumour cells and parallels tumour growth. It was found that mouse immunoglobulin heavy chains are unable to serve as substrate for the protein kinase activity of pp60src. Therefore, an indirect protein kinase absorption (PKA) test was initiated to demonstrate recognition of the protein kinase activity associated with the src-gene product. The availability of syngeneic mice and the corresponding ASV-transformed tumour cells should facilitate studies designed to elucidate the possible relationship between the cytoplasmic pp60src and ASV-induced tumour-specific surface antigens (TSSA), for example, by allowing the production of stable mouse hybridomas synthesizing antibodies specific for pp60src and TSSA.

[Detection of a common antigenic determinant in the major inner protein of unrelated oncoviruses]

A new heterologous system of radioimmunoassay (p24 of bovine leukemia virus--antiserum to Rous sarcoma virus) has been developed which demonstrated for the first time the existence of a common antigenic determinant in the major inner protein of unrelated oncoviruses: avian leukemia-sarcoma virus, bovine leukemia virus, mammalian type C viruses (mouse, hamster, monkey) and type D viruses (simian Mason-Pfizer virus). These data suggest a common origin of unrelated oncoviruses and open new approaches for the search of unknown agents associated with human and animal neoplastic diseases.

Radioimmunological comparison of the DNA polymerases of avian retroviruses

125I-labeled DNA polymerases of avian myeloblastosis virus and spleen necrosis virus were used in a radioimmunological characterization of avian retrovirus DNA polymerases. It was shown that avian leukosis virus and reticuloendotheliosis virus DNA polymerases do not cross-react in radioimmunoassays. Within the avian leukosis virus species, species-specific and type-specific antigenic determinants of the DNA polymerase were defined. The previous finding of genus-specific antigenic determinants in avian myeloblastosis virus and Amherst pheasant virus DNA polymerases was confirmed and extended to members of all subgroups of avian leukosis virus. It was shown that there is little immunological variation between the DNA polymerases of the four members of the reticuloendotheliosis virus species. Particles with RNA-dependent DNA polymerase activity from the allantoic fluid of normal chicken eggs and from the medium of a goose cell culture did not compete for the antibodies directed against any of the sets of antigenic determinants defined in this study.

Non-specific effects of avian retrovirus co-incubation on lymphocyte function: abrogation of antigen- and mitogen-induced proliferative responsiveness

Peripheral blood lymphocytes from chickens bearing tumours induced by avian retroviruses can be stimulated to divide by group-specific antigens present in supernatant fluids of avian retrovirus-infected but not normal chicken embryo fibroblast (CEF) cells. Centrifugation studies revealed that the relevant antigenic activity is non-virion in nature. Indeed, the presence of avian retrovirus particles was found to be inhibitory to the capacity of sensitized lymphocytes to be stimulated in this antigen-driven blastogenesis assay. Similar results were obtained in lymphocyte mitogenesis experiments in which any of peripheral chicken lymphocytes or mouse splenic, lymph node or thymic lymphocytes were co-incubated with either concanavalin A or phytohaemagglutinin in the presence of numerous types of virus particles. This inhibitory effect was not due to infection of lymphocytes by the viruses tested, and was obtained in the case of lymphocyte-virus combinations for which the cells lacked the surface receptors required for viral entry. Virus could be added to lymphocyte cultures as late as 26 h after co-incubation with mitogen, and still inhibit the usual mitogenic response. In addition, co-addition of virus to lymphocytes in the presence of concanavalin A was found to block the capping of ligand-bound receptors which normally ensues. Pre-added virus did not, however, affect the ability of lectins to bind to cells.

An enzyme-linked immunosorbent assay for detecting avian leukosis-sarcoma viruses

Immunoglobulins from antiserum raised against chromatographically purified avian myeloblastosis virus (AMV) group-specific (gs) antigens were used in enzyme-linked immunosorbent assay (ELISA). Readily discernible color was produced with 2--3 ng of AMV protein in microplate wells coated with 4 micrograms of salt-precipitated immunoglobulins. When a biological assay, i.e., phenotypic mixing (PM), was the criterion for the infectious status of specimens, the ELISA consistently identified a greater percentage of virus-positive specimens than direct complement-fixation (DCF) tests. Over 95% concordance was obtained between the ELISA and PM bioassays when meconia and whole-blood samples were tested. Moreover, three DCF(-) egg albumens from one virus shedder hen were positive by the direct ELISA. Complete agreement was found between a biological assay for endogenous virus and the ELISA when blood and albumens from inbred chickens were tested. The ELISA is a rapid and convenient alternative to the DCF test for identifying infected chickens in eradication programs, because virus-rich sources such as meconia and blood that are unsuitable for DCF can be tested directly.

Low incidence of lymphoid tumors in chickens continuously producing endogenous virus

A flock of 258 male and 243 female chickens of a cross of Regional Poultry Research Laboratory lines 15B and 7(2) were kept in a filtered-air positive-pressure house and observed for tumors from 100 to more than 729 days of age. These birds produced high titers of a subgroup E endogenous virus from the middle of the embryonic incubation period through the end of the experiment. No neoplasms were observed in the males. The females had two neoplasms indistinguishable from lymphoid leukosis and three other neoplasms not involving lymphoid cells. No evidence was found of infection with exogenous lymphoid leukosis viruses, Marek's disease virus, reticuloendotheliosis virus, or adenovirus (isolated on the isolation farm). Inoculation of another sample of this cross with a lymphoid leukosis virus of subgroup A resulted in 88% mortality with neoplasms (mostly lymphoid leukosis) by 167 days of age. The conclusion is that high levels of spontaneously produced endogenous virus do not induce high levels of neoplasms in chickens susceptible to lymphoid leukosis.

Neutralization of pseudotypes of vesicular stomatitis virus by sera from avian retrovirus-infected hosts

We investigated the capacity of lymphocytes and sera from chickens bearing tumors induced by avian sarcoma viruses (ASV) to interact with phenotypically mixed particles of vesicular stomatitis virus (VSV) and ASV. Immune chicken sera were able to specifically neutralize such VSV pseudotypes. This ability could be absorbed out, however, on purified preparations of avian retroviruses, suggesting that reactivity was primarily against avian retrovirus enveloped components. Supernatant fluids containing phenotypically mixed particles were unable to stimulate division of lymphocytes of tumor-bearing hosts, an ability possessed by culture fluids containing native ASV particles. Polyacrylamide gel analysis was unable to resolve any distinct pseudotype protein, which was not present in either of the parental virus types. Treatment with crude preparations of ultraviolet (UV)-irradiated VSV pseudotype material did not afford immunity against subsequent challenge with live ASV.

Influence of different routes of anti-tumor immunization: alternative induction of tumor immunity and tumor enhancement

Chickens and quails were immunized in parallel either i.v. or intramuscularly (i.m.) with lectin column-purified antigens from chick embryo cells that were transformed in vitro by avain sarcoma virus (ASV). After five to six injections, immunity of the animals was tested by challenge with ASV into the wing webs. Whereas tumor growth was inhibited after i.v. immunization with respect to incidence rate and time of tumor appearance, tumor growth was enhanced after i.m. injection. Animals that were injected with normal cell antigens served as controls. Spleen cells from only those animals that were immunized i.v. exerted a cytotoxic effect in vitro against ASV-transformed cells, whereas spleen cells from i.m. injected animals, in contrast, suppressed such cytotoxicity. The search for serum blocking or arming factors suggested that sera from i.m. injected animals block cellular cytotoxicity whereas sera from i.v. immunized animals render normal spleen cells cytotoxic (arming effect). The use of viruses from different subgroups and of antigens from gp85-lacking ASV-transformed cells indicates that immune effects were obtained against tumor cell surface antigens that differ from the antigen that is involved in virus neutralization (s-gp85).

Persistence of avian oncoviruses in chicken macrophages

Inoculation of avian oncoviruses into 1- to 2-month old chickens led to a rapid production of antiviral humoral antibodies. Under these conditions it was found that avian leukosis viruses are sequestered in macrophages of peripheral blood, in which they can persist for a long period of time (up to about 3 years). In contrast, avian sarcoma viruses were never found in macrophages from chickens during the progression of sarcomas or after regression of the tumors.

Incidence of viral antibodies in patients with various forms of cancer

The results of over 13,500 serological reactions performed in about 3,400 human sera collected from patients with various forms of cancer and from apparently healthy subjects have shown that the humoral immune reactivity of cancer patients as regards their viral antibody response is similar to that of apparently healthy subjects (blood donors or workers exposed to the risk of occupational contact with animal tumor viruses). The authors also remark the presence in the population of antibodies to some viruses with oncogenic potential proved so far only for mammals (adenovirus, SV-40, RSV) or to ubiquitous viruses (e.g. herpes virus) whose transforming activity has been demonstrated for several cell types in vitro and is suspected for some human tumors in vivo.

Effect of glucosamine on virus production and antigen expression in avian sarcoma virus-transformed cells

Treatment by glucosamine of avian sarcoma virus-transformed chicken embryo fibroblast (CEF) cells completely inhibited the formation of progeny-transforming virus particles. Such cells, however, could continue to synthesize non-infectious physical particles containing both viral RNA and the enzyme RNA-dependent DNA polymerase if glucosamine exposure was performed in the presence of glucose. Glucosamine treatment was found to affect antigenic expression in transformed CEF as measured by an indirect immunofluorescence test. Inhibition to a far lesser extent was observed when a lymphocyte stimulation assay for the detection of cell-mediated immunity was used in this system.

Peptide analysis of the transformation-specific antigen from avian sarcoma virus-transformed cells

Sera from rabbits bearing tumors induced by avian sarcoma virus (ASV) were ussed to immunopecipitate virus-specific proteins from extracts of chicken, hamster, and field vole cells transformed by ASV. Two virus-specific proteins having molecular weights of 76,000 and 60,000 were found in all cell lines examined. The 76,000-molecular-weight protein, Pr76, is the precursor to the internal core proteins of ASV. The 60,000-molecular-weight (60K) transformation-specific antigen from each cell line was subjected to peptide analysis, using chymotrypsin and Staphylococcus aureus V8 protease. The resulting peptide maps of the 60K protein from the different ASV-infected cell types were similar for each enzyme, strongly suggesting that the 60K protein is virus coded. Two-dimensional analysis of chymotryptic peptides from Pr76 and 60K reveals that 60K is not related to the gs antigen precursor. Radiolabeling of ASV-transformed cells with inorganic phosphate revealed that 60K is phosphorylated in vivo. The 60K proteins isolated from both ASV-transformed chicken and field vole cells were found to contain one tryptic phosphopeptide. The tryptic phosphopeptides of 60K from both cell lines migrated identically upon two-dimensional peptide analyses, and their migration differed from that of the principal phosphopeptide of Pr76.

Immunogenicity of the envelope glycoprotein of avian sarcoma virus

The expression of type E-specific glycoprotein in chick-helper factor-positive [chf(+)] chickens is not restricted to a certain stage of embryogenesis but persists in postembryonic life. This finding prompted an investigation of the immunogenicity of the viral envelope glycoprotein of exogenous avian sarcoma virus in chf(+) and chf(-) chickens. Sensitization of both classes of chickens resulted in the induction of detectable antibody reactivity to determinants of the glycoprotein that were type-specific as well as group-specific. Because group-specific determinants are present on type E-specific glycoprotein, these results link immunity to exogenous viral envelope glycoprotein in chf(+) chickens with autoreactivity. A model is proposed to rationalize the induction of reactivity in this system.

A complement fixing antigen in the livers of birds infected with an avian leukovirus (erythroblastosis virus)

Extracts of erythroblastosis affected livers from which much of the structural protein had been removed were prepared by acid denaturation. These extracts contained complement fixing "soluble" antigen in a form which was not associated with viral or subviral particles. Ultracentrifugation can be of assistance in separating complement fixation activity from contaminating material in these extracts.

Investigations on the incidence of complement fixing antibodies to the avian group-specific ("gs") sarcoma-leukosis antigen in fowl farm workers

The presence of complement fixing antibodies to the avian "gs" sarcoma-leukosis antigen is reported in the personnel of five different fowl farms. Seroconversion was observed in the workers from one of the farms, where the initial antibody incidence was very low.

The presence of complement fixing antibodies to the avian group-specific ("gs") sarcoma-leukosis antigen in the human population and in cancer patients

Antibodies to the avian group-specific "gs" sarcoma-leukosis antigen were made evident by complement fixation reaction in human sera collected from apparently healthy subjects and from patients with different forms of cancer and non-neoplastic diseases. The number of sera investigated was of 2,123. The possible mechanisms that might account for this paraimmune response of the human organism and the prospects of developing prophylactic steps against cancer are discussed.

A joint produce of the genes gag and pol of avian sarcoma virus: a possible precursor of reverse transcriptase

A virus-specific protein of approximately 180,000 daltons has been identified in cells transformed by avian sarcoma virus. The protein, designated P180, includes immunological determinants of both viral core proteins and reverse transcriptase. Its tryptic peptides represent essentially the sum of those of the precursor of the core proteins (Pr76gag) and reverse transcriptase. Thus P180 must arise from the uninterrupted translation of gag and pol. The kinetics of its formation and decay suggest that P180 is the precursor of reverse transcriptase.

Avian retrovirus-induced surface antigens and their cross-reactivity with chemically-transformed cells and primary embryonic cells of Japanese quails

By testing spleen cells from avian leukosis (ALV) and avian sarcoma virus (ASV)-injected Japanese quails in a microcytotoxicity assay against various target cells, we have demonstrated the existence of several target antigens. With non-transformed ALV-infected Japanese quail cells used as target cells, an avian retrovirus subgroup-specific destruction was obtained when spleen cells from animals infected with either avaian sarcoma or leukosis virus of the same subgroup were employed. This reaction is probably due to the virus envelope glycoproteins (Ve-gp) expressed on the cell surface. Apart from this subgroup-specific reaction, avian retrovirus group-specific destruction of ASV-transformed cells was demonstrated by means of effector cells immunized with ASV of a different subgroup. This reaction is restricted to transformed cells and not due to the virus envelope glycoprotein because the same effector cells are not cytotoxic to ALV-infected non-transformed cells but cytotoxic to sarcoma-virus-transformed cells which lack Ve-gp. Quail methylcholanthrene-tumor cells which show a transformation phenotype similar to that of ASV-transformed cells but which are free of detectable endogenous and exogenous retrovirus were also destroyed by the spleen cells from ASV tumorbearing animals. The same effector cells also exerted a weak cytotoxic effect on uninfected primary embryo cells but not to embryo cells after several passages.