[Detection of fps tumor antigen with mono-specific anti-fps serum in tumors induced by acute transforming ALV]

OBJECTIVE

To prepare anti-fps mono-specific serum, and detect the fps antigen in tumors induced by acute transforming avian leukosis/sarcoma virus containing v-fps oncogene.

METHODS

Two part of v-fps gene was amplified by RT-PCR using the Fu-J viral RNA as the template. Mono-specific serum was prepared by immuning Kunming white mouse with both two recombinant infusion proteins expressed by the prokaryotic expression system. Indirect immunofluorescent assay was used to detect fps antigen in tumor tissue suspension cells and CEF infected by sarcoma supernatant. Immunohistochemical method was used to detect fps antigen in tumor tissue.

RESULTS

The mouse mono-specific serum was specific as it had no cross reaction with classical ALV-J strains. The result reveals that the tumor tissue suspension cells, the CEF infected by sarcoma supernatant, and the slice immunohistochemistry of the sarcoma showed positive results.

CONCLUSION

The anti-fps mono-specific serum was prepared, and the detection method was established, which laid the foundation for the study of viral biological characteristics and mechanism of tumourgenesis of acute transforming avian leukosis/sarcoma virus containing v-fps oncogene.

Antibody binding in proximity to the receptor/glycoprotein complex leads to a basal level of virus neutralization

Hypothetically, antibodies may neutralize enveloped viruses by diverse mechanisms, such as disruption of receptor binding, interference with conformational changes required for virus entry, steric hindrance, or virus aggregation. Here, we demonstrate that retroviral infection mediated by the avian sarcoma-leukosis virus (ASLV-A) envelope glycoproteins can be neutralized by an antibody directed against a functionally unimportant component of a chimeric receptor protein. Thus, the binding of an antibody in proximity to the retroviral envelope glycoprotein-receptor complex, without binding to the entry machinery itself, results in neutralization. This finding provides additional support for the hypothesis that steric hindrance is sufficient for antibody-mediated neutralization of retroviruses.

Recombinant human polyclonal antibodies: A new class of therapeutic antibodies against viral infections

The mammalian immune system eliminates pathogens by generating a specific antibody response. Polyclonality is a key feature of this immune response: the immune system produces antibodies which bind to different structures on a given pathogen thereby increasing the likelihood of its elimination. The vast majority of current recombinant antibody drugs rely on monospecific monoclonal antibodies. Inherently, such antibodies do not represent the benefits of polyclonality utilized by a natural immune system and this has impeded the identification of efficacious antibody drugs against infectious agents, including viruses. The development of novel technologies has allowed the identification and manufacturing of antigen-specific recombinant polyclonal human antibodies, so-called symphobodies. This review describes the rationale for designing drugs based on symphobodies against pathogenic viruses, including HIV, vaccinia and smallpox virus, and respiratory syncytial virus.

Dual Requirement for the Igα Immunoreceptor Tyrosine-Based Activation Motif (ITAM) and a Conserved Non-Igα ITAM Tyrosine in Supporting Igαβ-Mediated B Cell Development

Surface Ig (sIg) expression is a critical checkpoint during avian B cell development. Only cells that express sIg colonize bursal follicles, clonally expand, and undergo Ig diversification by gene conversion. Expression of a heterodimer, in which the extracellular and transmembrane domains of murine CD8alpha or CD8beta are fused to the cytoplasmic domains of chicken Igalpha (chIgalpha) or Igbeta, respectively (murine CD8alpha (mCD8alpha):chIgalpha + mCD8beta:chIgbeta), or an mCD8alpha:chIgalpha homodimer supported bursal B cell development as efficiently as endogenous sIg. In this study we demonstrate that B cell development, in the absence of chIgbeta, requires both the Igalpha ITAM and a conserved non-ITAM Igalpha tyrosine (Y3) that has been associated with binding to B cell linker protein (BLNK). When associated with the cytoplasmic domain of Igbeta, the Igalpha ITAM is not required for the induction of strong calcium mobilization or BLNK phosphorylation, but is still necessary to support B cell development. In contrast, mutation of the Igalpha Y3 severely compromised calcium mobilization when expressed as either a homodimer or a heterodimer with the cytoplasmic domain of Igbeta. However, coexpression of the cytoplasmic domain of Igbeta partially complemented the Igalpha Y3 mutation, rescuing higher levels of BLNK phosphorylation and, more strikingly, supporting B cell development.

Genetic analysis of a divergent selection for resistance to Rous sarcomas in chickens

Selection for disease resistance related traits is a tool of choice for evidencing and exploring genetic variability and studying underlying resistance mechanisms. In this framework, chickens originating from a base population, homozygote for the B19 major histocompatibility complex (MHC) were divergently selected for either progression or regression of tumors induced at 4 weeks of age by a SR-D strain of Rous sarcoma virus (RSV). The first generation of selection was based on a progeny test and subsequent selections were performed on full-sibs. Data of 18 generations including a total of 2010 birds measured were analyzed for the tumor profile index (TPI), a synthetic criterion of resistance derived from recording the volume of the tumors and mortality. Response to selection and heritability of TPI were estimated using a restricted maximum likelihood method with an animal model. Significant progress was shown in both directions: the lines differing significantly for TPI and mortality becoming null in the "regressor" line. Heritability of TPI was estimated as 0.49 +/- 0.05 and 0.53 +/- 0.06 within the progressor and regressor lines respectively, and 0.46 +/- 0.03 when estimated over lines. Preliminary results showed within the progressor line a possible association between one Rfp-Y type and the growth of tumors.

Major histocompatibility (B) complex control of responses against Rous sarcomas

The chicken major histocompatibility (B) complex (MHC) affects disease outcome significantly. One of the best characterized systems of MHC control is the response to the oncogenic retrovirus, Rous sarcoma virus (RSV). Genetic selection altered the tumor growth pattern, either regressively or progressively, with the data suggesting control by one or a few loci. Particular MHC genotypes determine RSV tumor regression or progression indicating the crucial B complex role in Rous sarcoma outcome. Analysis of inbred lines, their crosses, congenic lines, and noninbred populations has revealed the anti-RSV response of many B complex haplotypes. Tumor growth disparity among lines identical at the MHC but differing in their background genes suggested a non-MHC gene contribution to tumor fate. Genetic complementation in tumor growth has also been demonstrated for MHC and non-MHC genes. RSV tumor expansion reflects both tumor cell proliferation and viral replication generating new tumor cells. In addition, the B complex controls tumor growth induced by a subviral DNA construct encoding only the RSV v-src oncogene. Immunity to subsequent tumors and metastasis also exhibit MHC control. Genotypes that regressed either RSV or v-src DNA primary tumors had enhanced protection against subsequent homologous challenge. Regressor B genotypes had lower tumor metastasis compared with progressor types. Together, the data indicate that B complex control of RSV tumor fate is strongly defined by the response to a v-src-determined function. Differential RSV tumor outcomes among various B genotypes may include immune recognition of a tumor-specific antigen or immune system influences on viral replication.

Resistance to infection by subgroups B, D, and E avian sarcoma and leukosis viruses is explained by a premature stop codon within a resistance allele of the tvb receptor gene

Here we present the first molecular characterization of the defect associated with an avian sarcoma and leukosis virus (ASLV) receptor resistance allele, tvb(r). We show that resistance to infection by subgroups B, D, and E ASLV is explained by the presence of a single base pair mutation that distinguishes this allele from tvb(s1), an allele which encodes a receptor for all three viral subgroups. This mutation generates an in-frame stop codon that is predicted to lead to the production of a severely truncated protein.

DNA vaccination against v-src oncogene-induced tumours in congenic chickens

DNA vaccination is particularly efficient for induction of cytotoxic T-lymphocyte (CTL) response. In our experiments, we used MHC(B) congenic chicken lines CB and CC (regressors and progressors of v-src-induced tumours, respectively) and a mutated, non-oncogenic v-src gene construct as the DNA vaccine. A high degree of vaccine protection against oncogenic v-src challenge was achieved in the CB line chickens. CTL response was demonstrated in vitro and by adoptive transfer of immune cells to the syngeneic host and to the CC line chickens rendered tolerant to CB cells. In the CC line chickens we observed tumour growth retardation after a low-dose DNA vaccination administered to immature recipients while higher amounts of DNA vaccine in immunocompetent chickens exerted an enhancing effect.

Nonmajor histocompatibility complex alloantigen effects on the fate of Rous sarcomas

Rous sarcoma virus-induced tumor outcome is controlled by the MHC (B). Additional data, using controlled segregation in families, has indicated non-MHC effects as well, but few studies have focused on blood groups other than the B complex. Segregating combinations of genes encoding erythrocyte (Ea) alloantigen systems A, C, D, E, H, I, P, and L in B2B5 and B5B5 MHC (B) backgrounds were examined for their effects on Rous sarcomas. Six-week-old chickens were inoculated in the wing-web with 30 pfu of Rous sarcoma virus (RSV). Tumors were scored six times over a 10-wk period. A tumor profile index (TPI) was assigned to each chicken based on the six tumor size scores. Response was evaluated using tumor size at each measurement period, TPI, and mortality. The genotypes of Ea systems A, C, D, E, H, I, and P had no significant effect on any parameter in either B complex population. The Ea-L system had an effect on Rous sarcomas in the B2B5 intermediate responders and B5B5 progressors. Tumor size, TPI, and mortality were all significantly lower in B2B5 L1L1 chickens than in B2B5 L1L2 chickens. Mortality was lower in the B5B5 L1L1 birds than in B5B5 L1L2 chickens. It appears that the Ea-L system, or one closely linked, is acting in a manner independent of the B complex in response to RSV challenge.

The genetics of mortality and survival of broiler chicks infected as embryos by subgroup A Rous sarcoma virus

A study using two high-performance broiler lines, a synthetic male line (SML) and a synthetic dam line (SDL), was undertaken to investigate the pattern of mortality due to induced liver tumours (LT) and the immune response to subgroup A virus inoculated via the chorioallantoic membrane (CAM) route. The distribution patterns of the four possible phenotypes were similar in both sire and dam lines. The occurrence of conversely associated phenotypes was about 30S, in both the lines. The percentages of CAM(+) LT(-) and CAM(-) LT(+) were 14.26%, and 14.46% in the dam line and 20.0% and 9.57% in the male line. The LT mortality was 30-50% in the birds with low pock counts, whereas it was 80-93% in the birds with high pock counts. The group specific antigen shedding status did not influence death due to LT. In birds in the high pock count group, 98% of deaths due to LT were completed by the sixth week, whereas in those in the low pock count group, death due to LT was spread over 24 weeks. The SDL birds survived better than SML birds in the high pock count groups. In both lines, about 20% of deaths occurred owing to non-specific causes. The average survival time after hatching before death from LT was 26 days, whereas that for non-specific death was 81 days.

Genes of chicken MHC regulate the adherence activity of blood monocytes in Rous sarcomas progressing and regressing lines

The influence of the chicken major histocompatibility (B) complex (MHC) on the adherence potential of monocyte-derived macrophages was examined using the congenic chicken lines CB and CC. These lines represent well-defined genetic models for the study of resistance (CB) or susceptibility (CC) to the progressive growth of Rous sarcomas. Using a monoclonal antibody specific for chicken monocytes/macrophages, CB and CC chickens were shown by flow cytometry analyses to have similar proportions of peripheral blood monocytes. However, when the glass-adherence potential of these cells was compared during incubation in tissue culture medium over 24, 48 and 72 h at 40 degrees C, significant differences were seen between cells from these two inbred lines. After 24 and 48 h, glass-adherence by CB cells was 2-3 fold higher than that of CC cells. After 72 h this difference decreased to 1.5 fold. At 24 and 48 h, the adherent CB macrophages also appeared about 1.5 times larger than those of CC chickens. Genetic analysis using F1 hybrids (CBxCC) showed that this trait is regulated by a dominant gene that segregates with the B12 haplotype in the backcross generation F1xCC. From the results obtained with the recombinant congenic lines CB.R1 and CC.R1, we conclude that the gene regulating adherence potential is localized within the B-F/L region of the chicken MHC. About 50% of adherent cells were able to phagocytose opsonised FITC-labelled Zymosan particles. The level of nitric oxide production in vitro by CB and CC macrophages was equal. The importance of cells of the mononuclear phagocyte system for the response to Rous sarcoma virus (RSV) infection was studied in CB chickens using the anti-macrophage agents silica, carrageenan, and C12MDP, encapsulated in liposomes. In those chickens treated with silica and carrageenan, we observed progressive growth of RSV-induced tumors. The graft-versus-host reactivity of peripheral blood lymphocytes (PBL) of treated chickens was comparable to controls. In vitro nitric oxide production by macrophages from silica-treated chickens was higher than by macrophages from untreated controls.

The genetic control of susceptibility to subgroup D RNA tumour virus infection in commercial breeds of chickens

The genetic control of resistance to RSV (RAV-50) in chick embryos inoculated via the chorioallantoic membrane route was studied in three breeds of chickens. The relative susceptibility to subgroup D infection was 0.01, 0.02 and 0.003 in broilers, White Leghorns and Bantam x Australorp crosses, respectively. The distribution pattern of putative dr gene frequencies were 0.80, 0.68 and 0.90, respectively, in the same three breeds. Liver tumours resulting from the virus infection were observed in a very few birds about 28 days after hatching.

Highly specific antibody to Rous sarcoma virus src gene product recognizes nuclear and nucleolar antigens in human cells

An antiserum to the Rous sarcoma virus-transforming protein pp60v-src, raised in rabbits immunized with the bacterially produced protein alpha p60 serum (M. D. Resh and R. L. Erikson, J. Cell Biol. 100:409-417, 1985) previously reported to detect very specifically a novel population of pp60v-src and pp60c-src molecules associated with juxtareticular nuclear membranes in normal and Rous sarcoma virus-infected cells of avian and mammalian origin, was used here to investigate by immunofluorescence microscopy localization patterns of Src molecules in human cell lines, either normal or derived from spontaneous tumors. We found that the alpha p60 serum reveals nuclear and nucleolar concentrations of antigens in all the human cell lines tested and in two rat and mouse hepatoma cell lines derived from adult tumorous tissues but not in any established rat and mouse cell lines either untransformed or transformed by the src and ras oncogenes. Both the nuclear and nucleolar stainings can be totally extinguished by preincubation of the serum with highly purified chicken c-Src. We show also that the partitioning of the alpha p60-reactive proteins among the whole nucleus and the nucleolus depends mostly on two different parameters: the position in the cell cycle and the degree of cell confluency. Our observations raise the attractive possibility that, in differentiated cells, pp60c-src and related proteins might be involved not only in mediating the transduction of mitogenic signals at the plasma membrane level but also in controlling progression through the cell cycle and entry in mitosis by interacting with cell division cycle regulatory components at the nuclear level.

Transport of a lysosomally targeted Rous sarcoma virus envelope glycoprotein involves transient expression on the cell surface

The details of intracellular transport pathways for glycosylated proteins remain incompletely described. We previously described a mutant Rous sarcoma virus envelope glycoprotein (gp), mu 26, with an altered membrane-spanning domain that was targeted to lysosomes after traversing the trans-Golgi. This mutant protein was not detectable on the cell surface by immunofluorescence, but its pathway for degradation remained unclear. To investigate this we have employed a second env mutation, S19, that results in a protein which is defective for normal cleavage/activation by intracellular enzymes, but remains susceptible to cleavage by extracellular proteases. Cleavage/activation of the double mutant by trypsin, which could only occur if it was exposed on the cell surface, was observed, indicating that the plasma membrane is an intermediate destination in the transport of this mutant protein. To substantiate these results, cells expressing the mu 26 glycoprotein were incubated with an antibody specific for the native protein in the presence of chloroquine. The specific accumulation of this antibody/gp complex in vesicles, as detected by internal immunofluorescence, confirmed the trypsin cleavage results. We conclude that this rapidly degraded mutant protein is transported from the trans-Golgi to the cell surface, where it is only transiently exposed, and then rapidly endocytosed and lysosomally degraded. The relevance of these results to the targeting of lysosomal proteins is discussed.

Major histocompatibility (B) complex control of the formation of v-src-induced metastases

Previous observations have shown that the major histocompatibility (B) complex is a determinant of the growth of v-src-induced primary tumors. In the present study, we have observed with two chicken lines congenic for B complex alleles that the control of v-src-mediated oncogenesis by the B complex extends to metastasis formation. In addition, our results show that the differences in metastasis frequencies between these two lines are correlated with the relative strengths of their respective tumor immune responses.

The leukocyte response of Japanese quail to Rous sarcoma virus-induced tumors

In male Japanese quail, different circulating leukocyte responses were observed for progressors (birds developing a massive tumor that persisted throughout the experiment) and regressors (birds developing a tumor that gradually disappeared) after initial challenge with Rous sarcoma virus (RSV). Blood was sampled before and at weekly intervals postinoculation. Blood smears were prepared and stained with Diff Quik, and a light microscope (1000 x) was used in a direct count of 50 fields. Leukocytes were classified as heterophils, lymphocytes, monocytes, or eosinophils. The significant increase (P < 0.05) in total leukocytes at 14 days in regressors and progressors was consistent with the increase in tumor growth. The regressors' individual percentage of leukocytes did not deviate from control values, whereas the progressors' percentages of heterophils and monocytes were significantly higher (P < 0.05) and of lymphocytes significantly lower (P < 0.05) than those of controls by 14 days postinoculation. Indicative of this was the progressors' heterophil to lymphocyte ratio, which was significantly higher (P < 0.05) than that of controls 14 days post RSV challenge and remained elevated throughout the experiment. These findings suggest that the progressors' immune response is suppressed by proliferation of malignant cells. Therefore, the heterophil to lymphocyte ratio may be used in addition to tumor size to identify those birds that will regress RSV-induced tumors.

Analysis of macrophage functions in Rous sarcoma-induced tumor regressor and progressor 6.B congenic chickens

Macrophage functional competence was studied in two congenic chicken lines 6.6-2 (B2B2) and 6.15-5 (B5B5) which are regressors and progressors, respectively, of Rous sarcoma-induced tumors. Sephadex-elicited abdominal exudate cells (AEC) were harvested from 4-week-old chickens to determine their total number, glass adherence potential, percentage of adherent macrophages and phagocytosis of antibody coated (ops) and uncoated (unops) sheep red blood cells (SRBC). Tumoricidal abilities of culture medium conditioned with lipopolysaccharide treated macrophages and of macrophages cocultured with target cells were assessed against 51Cr-labelled tumor cell targets. The congenic lines did not differ in total AEC or percent macrophages. However, AEC from B5B5 birds exhibited significantly lower (P < 0.05) glass-adherence potential than AEC from B2B2 birds exhibited significantly lower (P < 0.05) glass-adherence potential than AEC from B2B2 birds. The percentage of phagocytic macrophages did not differ between lines for unop-SRBC, whereas a higher percentage of B5B5 compared with B2B2 birds (P < 0.05) macrophages phagocytized ops-SRBC. Macrophages from B5B5 birds had significantly (P < 0.05) lower activity in both tumoricidal tests. These results imply that the tumor progression in B5B5 birds is associated with reduced activation of macrophages towards a tumoricidal pathway.

Genetic susceptibility of indigenous chicks to subgroup A Rous sarcoma virus inoculated via the chorioallantoic membrane

An investigation was made using chicks of two Indian indigenous breeds of fowl, Kadaknath and Aseel, to ascertain genetic resistance to infection by Rous sarcoma virus of subgroup A. A standard inoculation dose of 0.2 ml virus containing 1000 pock forming units ml-1 was injected via the chorioallantoic membrane (CAM) into the 11-day-old embryos that were subsequently hatched. The sensitivity of the two indigenous breeds was compared with the highly susceptible exotic White Leghorn (WL) strain maintained in the laboratory. The Kadaknath breed was about three-fold and Assel, about six-fold less sensitive than the WL strain, indicating superiority of the indigenous breeds over the exotic breed of fowl. Most of the CAM-susceptible chicks died of liver tumour (LT) and most of the CAM-resistant chicks survived. However, conversely associated tumour phenotype subclass chicks, i.e. CAM-susceptible LT-negative chicks that survived and CAM-resistant LT-positive chicks that died, occurred consistently in the three breeds of fowl. Nevertheless, the overall survival potential of Kadaknath chicks measured up to 8 weeks post-hatching was greater than that of Aseel chicks. Neither transformation of embryonic tissue prior to hatching nor the visceral metastasis including liver conformed with the degree of CAM-infection as measured by number of pocks on CAMs.

Frequency of chicken CD4+ and CD8+ cells. Genetic control and effect of Rous sarcoma virus infection

In chickens from congenic inbred lines CB and CC that differ only in the major histocompatibility complex (MHC), we observed significantly different percentages of CD4+ and CD8+ cells in peripheral blood lymphocytes (PBL) and spleen. Positive cells were detected by indirect immunofluorescence test as analysed by flow cytometry. In both PBL and spleen cell suspensions, the number of CD4+ cells was significantly higher in CB than in CC chickens, whereas in CC birds there was a higher percentage of CD8+ cells than in CB. These statistically significant differences were under the MHC control. We found no statistically significant influence of regressions or progression of Rous sarcoma virus-induced tumours on the percentage of peripheral T cells and on the interleukin-2 production in vitro.

Avian retroviral recombinant expressing foreign envelope delays tumour formation of ASV-A-induced sarcoma

An avian recombinant retrovirus expressing subgroup A envelope glycoprotein antigenicity, RAV-0-A1, significantly delayed sarcoma induction in chickens after challenge with ASV-A. When tumours were formed, significantly smaller tumours resulted. The mechanism of protection does not appear to be interference mediated, since virus was not detected in the chickens. Protection was correlated with both neutralizing and complement-dependent cytotoxic antibodies (CDCA).

Action spectrum of antiviral factor from chicken sera

Rous sarcoma virus infections of regressor line chickens stimulate the transient production of antiviral factors in the serum. Earlier the present authors reported that a viral neutralization factor (VNF) inactivated Rous sarcoma virus during a 3-h incubation. The VNF is likely to have a broad antiviral and antimicrobial spectrum because it is active against several unrelated pathogenic poultry viruses. The present study measured the activity of VNF against Newcastle disease virus, infectious bursal disease virus, and infectious bronchitis virus. The VNF is active in immunologically incompetent systems and must be preincubated with the virus in order to inhibit it. Based upon the current experiments, it is proposed that VNF is not an immunomodulator but directly inactivates the virus. The VNF agent appears to be one of a newly identified class of nonspecific antiviral agents produced in vivo in chickens in response to a viral infection.

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.

Nonspecific immunoprotection against Rous sarcoma tumor in chicks

An enzyme treated preparation of saprophytic Mycobacterium phlei, referred as NSI, when administered intramuscularly has been found to protect the chicks against Rous Sarcoma Virus induced tumor. A protection level of 35.4%, 24.1% and 21.2% were observed when challenged on 10th, 20th and 30th day post NSI inoculation. The tumor growth inhibitory-activity of NSI was significant (P less than 0.01). Both, systemic and intralesional administration of NSI exhibited significant tumorostatic activity (P less than 0.05). NSI stimulated the cell mediated immune response to specific as well as to nonspecific Rous sarcoma antigen. These studies indicated the immunopreventive activity of NSI against Rous sarcoma tumor which had an immunogenic basis.

Suppression of Rous sarcoma virus-induced tumor formation by preinfection with viruses encoding src protein with novel N termini

Two recovered avian sarcoma viruses (rASVs), rASV157 and rASV1702, encode src products which contain novel, nonmyristoylated N-terminal amino acids. These viruses transform chicken embryo fibroblasts and cause tumors in chicks. However, the tumors rASVs induce are small and regress within 2 weeks. To determine whether this regression results from weak tumorigenicity or from the active immunity of the host, we injected 1-week-old chicks with rASV and several days later injected the chicks with challenge virus of a different subgroup. Of the rASV1702-preinfected chicks challenged 5 days later with Rous sarcoma virus (RSV), 40% showed no subsequent tumor formation and 60% formed tumors which regressed within 1 week. The potency of this protective effect depended on the dosage of preinfection virus used and increased as the interval between preinfection and challenge infection was lengthened (when the interval was 9 days, none of the challenged chicks formed tumors). rASV157-preinfected chicks challenged with RSV after 9 days showed only partial protection: 42% formed tumors which regressed, whereas 58% formed tumors which continued to grow. Challenging rASV-preinfected chicks with Fujinami sarcoma virus or a RSV vector encoding the v-fps oncogene or polyomavirus middle T resulted in no suppression of tumor formation. Preinfection with src mutants or a RSV vector encoding polyomavirus middle T antigen, both of which induce slow-growing tumors, failed to elicit the protective effect. Finally, a novel N-terminal domain encoded by rASV1702 src was shown to be involved in but not sufficient for full protection. These data indicate that determinants on or induced by rASV157 and rASV1702 can elicit a potent protection against the tumorigenic potential of RSV-encoded p60v-src.

Association of polyoma virus middle T antigen and pp60src with cytoskeletal elements

Polyoma virus middle T antigen (mT) as well as pp60v-src, the oncogene product of Rous sarcoma virus, associate with membranes and cytoskeletal structures in virus-infected cells. Furthermore, mT has been shown to be tightly bound to pp60c-src, the cellular homolog of pp60v-src. While the presence of pp60v-src in focal contacts has been demonstrated, the localization of mT and pp60c-src is less clear. We show here that mT is associated with focal contacts and that the phosphorylated protein can be immunoprecipitated with anti-vinculin serum. We suggest that the mT/pp60c-src complex and pp60v-src are tightly bound to vinculin. This interaction may be relevant in the process of cell transformation since disorganization of the actin filament network seems to play an important role in the deregulation of cell growth observed in tumor cells.

Resistance of chickens to Rous sarcoma virus challenge following immunization with a recombinant avian leukosis virus

An attenuated recombinant avian leukosis virus (ALV) produced by recombinant DNA techniques was examined for its ability to provide resistance to Rous sarcoma virus (RSV) challenge. Specific-pathogen-free chicken embryos (18-day incubation) and hatched chicks inoculated with recombinant ALV produced significantly smaller tumors than sham-inoculated controls upon challenge with RSV 2 weeks postinoculation; inoculation with RAV-1 produced similar results. Specific-pathogen-free hens inoculated with recombinant ALV produced viral-protein-specific antibody that was transmitted to 100% of the progeny, as detected by enzyme-linked immunosorbent assay. Progeny of the inoculated hens produced significantly fewer tumors than sham-inoculated controls upon challenge with RSV at hatch, indicating that maternal antibody may be a factor in resistance to tumor development.

Neural differentiation, NCAM-mediated adhesion, and gap junctional communication in neuroectoderm. A study in vitro

We studied the development of NCAM and gap junctional communication, and their mutual relationship in chick neuroectoderm in vitro. Expression of NCAM, as detected by monoclonal and polyclonal antibodies, and development of junctional communication, as detected by extensive cell-to-cell transfer of 400-500-D fluorescent tracers, occurred in cultures from stage-2 embryos onward. Both expressions presumably required primary induction. The differentiating cells formed discrete fields of expression on the second to third day in culture, with the NCAM fields coinciding with the junctional communication fields delineated by the tracers. Other neural differentiations developed in the following order: tetanus toxin receptors, neurofilament protein, and neurite outgrowth. Chronic treatment with antibody Fab fragments against NCAM interfered with the development of communication, suggesting that NCAM-mediated adhesion promotes formation of cell-to-cell channels. Temperature-sensitive mutant Rous sarcoma virus blocked (reversibly) communication and the subsequent development of neurofilament protein and neurites, but expression of NCAM continued.

Inhibition of HLA class I antigen and mRNA expression induced by Rous sarcoma virus in transformed human fibroblasts

Cells from various human nonlymphoreticular neoplasms show reduced HLA class I antigen expression. In this report, a system of human fibroblasts transformed by an avian retrovirus has been employed to investigate the mechanism of this phenomenon. Rous sarcoma virus has been used to transform in vitro human dermal fibroblasts, and clonal cell lines have been established from these cultures. In all the clones studied the integration of the provirus induced a reduction of cell-surface HLA-A, -B, -C framework antigen and beta 2-microglobulin expression when compared to levels for the respective parental fibroblasts. The reduction was correlated with a diminished intracellular synthesis of these molecules. Uninfected cells derived from an osteogenic sarcoma exhibited a reduced expression comparable to that of dermal diploid fibroblasts obtained from the same donor and transformed by Rous sarcoma virus. RNA gel blot analysis of total cellular RNA and of poly(A)+ cytoplasmic RNA showed a markedly decreased amount of HLA class I transcripts in the transformed cells. Southern blot study of genomic DNAs digested with several restriction endonucleases showed that the banding patterns of the HLA genes were not altered in the cells harboring the Rous sarcoma provirus. Our data are consistent with the hypothesis that the Rous sarcoma provirus that does not seem to be linked to the major histocompatibility complex class I gene superfamily may negatively control HLA gene expression.

Epitope mapping of monoclonal antibodies to gag protein p19 of avian sarcoma and leukaemia viruses

We have characterized a set of 15 monoclonal antibodies to p19gag, one of the internal proteins of avian sarcoma and leukaemia viruses. All the antibodies work in immune precipitations as well as in immunoblotting, though with different efficiencies. We have developed a simple epitope mapping technique, which uses partial chemical cleavages at methionine or tryptophan residues followed by immunoblotting from SDS-polyacrylamide gels, to localize the epitopes of nine of these antibodies. The epitopes fall into at least four classes. The mapping procedure should also be useful for other antigens of known primary structure.

Immunization with envelope glycoprotein of an avian RNA tumor virus protects against sarcoma virus tumor induction: role of subgroup

Avian RNA tumor virus envelope glycoprotein protects against sarcoma development by an avian sarcoma virus of the same subgroup. Avian RNA tumor viruses, members of the retrovirus family, induce various malignancies in fowl (Weiss et al. (eds.), 1982, RNA Tumor Viruses, Cold Spring Harbor, N.Y.). These viruses consist of a genomic RNA core surrounded by an envelope with embedded glycoproteins, of 85 and 37 kDa. The 85 kDa glycoprotein is antigenically specific for each subgroup as determined by neutralization. The envelope glycoprotein can be removed from the virion with retention of its antigenicity (Duesberg et al., 1970, Virology 41, 631-646). Two fractions of 4-6S and 8S, separated by sedimentation, were shown to retain antigenicity by interference of neutralization of virus by antibody. Thus, the 4-6S and 8S preparations could possibly serve as immunogens. The objective of this study was to determine if such envelope glycoprotein preparations could function as potential vaccines, and if so, whether the protection afforded would be subgroup specific.

Mutations within the proteolytic cleavage site of the Rous sarcoma virus glycoprotein that block processing to gp85 and gp37

We have investigated the specificity of the proteolytic cleavage of the Rous sarcoma virus glycoprotein precursor by introducing two mutations into the putative cleavage region (Arg-Arg-Lys-Arg). We show that neither a deletion of the cleavage sequence nor a glutamic acid for lysine substitution altered intracellular transport or surface expression of the env gene products. However, both the four-amino-acid deletion and the glutamic acid substitution block processing of the env precursor. Susceptibility of the glutamic acid-substituted env precursor to proteases indicated that tertiary protein structure was unaffected. While inhibitor experiments suggested that more than one endopeptidase might be capable of mediating the proteolytic cleavage, the results presented here point to the presence in the Golgi apparatus of a novel endopeptidase, required for retroviral glycoprotein cleavage, that has a high specificity for lysine-containing peptides.

The immune status of avian sarcoma virus-infected chickens as a determinant of sarcoma growth pattern and viral antigen expression

Patterns of sarcoma growth were compared in immune-suppressed (cyclophosphamide-treated) vs nonsuppressed avian sarcoma virus-infected chickens. Sarcomas were initially induced in suppressed or nonsuppressed line FP chickens (donors) by wing web inoculation with clone 85, an avian sarcoma virus encoding an envelope glycoprotein that is non-antigenically cross-reactive with endogenous viral glycoprotein. Sarcoma tissue from these donors was then implanted in the wing webs of suppressed or nonsuppressed recipients to compare the effects of immune suppression of donors and of recipients. Sarcoma tissue that had been excised from suppressed donors and implanted in the wing webs of nonsuppressed recipients evidenced a much greater capacity than sarcoma tissue from nonsuppressed donors to yield distal sarcomas localized to visceral organs and to induce expansion by infection-mediated recruitment of new sarcoma cells. In contrast, immune suppression of the recipients of sarcoma tissue from nonsuppressed donors was not significantly enhancing for these effects. The enhancement achieved by immune suppression of the donors correlated with a markedly increased level of virus production and viral antigen expression by the primary (wing web) sarcoma cells from these donors.

Integration and expression of provirus in human cells transformed by avian sarcoma virus

Previously, human diploid fibroblasts from some donors infected in vitro by avian sarcoma virus (ASV) were transformed and found, by electron microscopy, to produce small numbers of virus particles that were infectious by bioassay; also, a line of human osteosarcoma cells infected with ASV developed additional characteristics of transformation and released a small number of infectious virus particles. In this study the complete proviral sequence was shown to be integrated in the genome of these cells. The env-related proteins gp85 and gp37 and the gag-related proteins pr76, pr60, and p19 can be detected in cytoplasmic extracts of ASV-infected human cells. Comparable amounts of pp60v-src were found in human and avian cells infected with ASV. The associated kinase activity in infected human cells was dramatically increased as compared to that of uninfected controls; the enzyme had the same cation and substrate requirements as those from ASV-transformed avian cells. Replicating particles from infected human cells were purified and were significantly modified compared to those from avian hosts as shown by a) higher specific gravity, b) the presence of RSV gag-related but not env-related antigens, and c) the fact that the virus-associated reverse transcriptase preferred the divalent cations Mn2+ and Fe2+ over Mg2+.

Recognition of Rous sarcoma virus-induced tumor antigens by cytotoxic T lymphocytes (CTL): studies on specificity of killing by CTL employing H-2 congenic and recombinant mouse tumor cells

The specificities of cytotoxic T lymphocytes (CTL) were studied for the analysis of CTL against tumor-specific cell surface antigen(s) (TSSA) of non-virus-producing tumor cells induced by the Schmidt-Ruppin strain of Rous sarcoma virus (SR-RSV) in B10 congenic and recombinant mice. Eight CTL clones were established from immune spleen cells of B10.A(5R) mice. These clones demonstrated six patterns of cytotoxic reactivity in vitro: Two clones showed H-2 restriction in tumor cell lysis. Two other clones had the capacity to lyse syngeneic, H-2K-compatible B10 and H-2-incompatible B10.A(4R) tumor cells, but not YAC-1 cells. One clone had cytotoxic activity against syngeneic, H-2D-compatible B10.D2 tumor cells and YAC-1 cells, but not against H-2-incompatible tumor cells. One clone had cytotoxic activity against syngeneic and YAC-1 tumor cells, but not against either H-2-compatible or H-2-incompatible tumor cells. One clone had lytic activity to syngeneic, H-2-compatible, H-2-incompatible, and YAC-1 tumor cells. Another clone killed H-2-incompatible B10.A(4R) tumor and YAC-1 cells, but not syngeneic or H-2-compatible tumor cells. All these clones strongly expressed surface Thy-1.2 antigens, whereas the expression of Lyt-1.2 and Lyt-2.2 antigens was different from clone to clone. These results demonstrate heterogeneity of both lytic specificity and phenotype of CTL against RSV-induced mouse tumor cells, suggesting the existence of multiple antigenic sites on the RSV TSSA recognized by CTL populations.

Expression of endogenous retroviral envelope glycoprotein as a determinant of immunity to Rous sarcoma

To analyze the effect of the expression of endogenous retroviral envelope glycoprotein on tumor immunity, patterns of sarcoma growth were compared in inbred FP line chickens infected with either of two strains of avian sarcoma virus, Pr-B (subgroup B) or cl.85 (subgroup G). These viruses were chosen for analysis because the envelope glycoprotein of Pr-B, but not of cl.85, is antigenically cross-reactive with the endogenous retroviral envelope glycoprotein expressed in the FP line. Inoculation of 1-day-old hatchmates with either virus yielded a significant percentage of chickens with distal sarcomas localized to visceral organs. By contrast, a marked difference in the percentage of chickens bearing distal sarcomas was noted when sarcoma tissue excised from virus-inoculated donors was implanted in 1-day-old recipients; a high proportion of the recipients of Pr-B-induced sarcoma tissue (Pr-B-sarcoma recipients), but only a low proportion of the cl.85-sarcoma recipients, exhibited distal sarcomas. At 3 weeks posthatch, a significantly higher percentage of donor-derived cells was detected in the primary tumors of the cl.85- versus the Pr-B-sarcoma recipients. A model of immune control, premised on the tolerogenicity of endogenous viral glycoprotein, is proposed to rationalize these results.

A glial fibrillary acidic protein-expressing and tumorigenic cell line derived from an avian sarcoma virus-induced rat astrocytoma

A permanent cell line, S635c15, was derived from an anaplastic astrocytoma induced by the Schmidt-Ruppin strain of avian sarcoma virus (ASV) in a female F-344 rat. Persistent expression of the astrocytic differentiation protein, glial fibrillary acidic protein (GFAP), was detected both in cultured cells after 100 passages in vitro and in transplanted tumors. Subcutaneous and intracerebral transplantation of S635c15 cells in syngeneic rats resulted in a 100% tumor incidence and a reproducible mortality distribution. S635c15 cells formed discrete masses after subcutaneous injection but grew intracranially as infiltrative lesions. Tumor blood flow and blood-to-tissue transport studies yield comparable values to other rat glioma models; S635c15 intracranial tumors proved to be a homogeneous model with little variation within and between tumors with respect to morphology, GFAP expression, blood flow, and permeability. This cell line provides a GFAP-expressing brain tumor model that extends the use of autochthonous ASV-induced astrocytomas by allowing in vitro and in vivo studies. It may be useful for further studies in neurobiology and brain tumor biology, diagnosis, and therapy.

Region coding for subgroup specificity of envelope of avian retroviruses does not determine lymphomagenicity

The purpose of this study was to test whether the region coding for subgroup envelope specificity was a determinant of oncogenic potential. An avian retrovirus recombinant was constructed to contain the envelope gene (env) determinant for subgroup A of an avian RNA tumor virus in one of the non-oncogenic, endogenous avian retroviruses, RAV-0. The results show that such a recombinant virus does not induce lymphoma when injected into susceptible, newborn chicks. Thus, it is concluded that the envelope determinant for subgroup of avian RNA tumor viruses does not determine malignant potential.

Localization of conserved and nonconserved epitopes within the Rous sarcoma virus-encoded src protein

We investigated the location of binding sites of pp60src-specific monoclonal antibodies by immunoprecipitating a panel of structurally altered src proteins. Two families of antibodies which recognized epitopes mapping to either amino acid residues 28 to 38 or 92 to 128 were identified. The highly conserved nature of the epitope defined by residues 92 to 128 suggests that it may represent an important functional region of the cellular src protein.

Ablation of humoral immunity in 15I5 x 72 chickens is not predisposing to the formation of subgroup G virus-induced distal sarcomas

Clone (cl.) 85 infection of 15I5 x 72 chickens at 4 weeks posthatch results in a lower frequency of distal sarcomas than does Prague (Pr)-B infection. As higher titers of virus-neutralizing antibody are generated in the cl.85-infected chickens, the possibility was addressed in the present study that the low frequency of cl.85-induced distal sarcomas is a direct consequence of the strong neutralizing response. Our observations indicate that ablation of humoral immunity by embryonic bursectomy does not serve to increase this frequency, implying that the antiviral humoral response is not required to limit formation of cl.85-induced distal sarcomas.

Isolation of monoclonal antibodies specific for Rous sarcoma virus structural, polymerase and transforming proteins and their use for the study of mutant virus-infected cells

Monoclonal antibodies were developed that are specific for Rous sarcoma virus structural, polymerase (reverse transcriptase) and transforming proteins. The monoclonal antibodies were shown to bind to purified virus proteins in an indirect 125I-labelled Protein A binding assay suitable for screening even very large numbers of hybridomas. Additional tests for specificity included radioimmunoprecipitation of purified virus structural proteins P12 and P27, of reverse transcriptase subunits alpha and beta, and of the transforming protein pp60v-src. Pilot immunofluorescence and protein kinase assays of the expression of virus proteins in avian and mammalian cells infected by wild-type virus as well as by temperature-sensitive, transformation-defective virus mutants revealed that synthesis of virus structural and transforming proteins is hardly affected by changes in temperature, whereas the pp60v-src-associated kinase activity is temperature-sensitive in cells infected by most, but not all the virus mutants.

Parabiosis between avian embryos resistant and susceptible to Rous sarcoma virus

Parabiosis of chicken embryos was used to determine if resistance or susceptibility to Rous sarcoma virus (RSV) tumors could be transferred between RSV-resistant (R) and RSV-susceptible (S) embryos. Eggs from RSV-R and RSV-S lines were parabiosed at 12 days of incubation. One week after hatching the chicks were inoculated in the wing web with RSV. Birds were examined for tumor lesions through 9 weeks of age. Lesion scores of the nonparabiosed RSV-S line were significantly higher than nonparabiosed RSV-R lines. Lesion scores of RSV-R chicks that had been parabiosed to RSV-S chicks were higher than nonparabiosed RSV-R chicks. Lesion scores of RSV-S chicks parabiosed to RSV-R chicks were not different from nonparabiosed RSV-S chicks. These results suggest that the resistance to RSV was not transferred between parabionts but that there was significant transfer of susceptibility from the RSV-S embryos to the RSV-R embryos.

Tests of association of lymphocyte alloantigen genotypes with resistance to viral oncogenesis in chickens. 2. Rous sarcoma and lymphoid leukosis in progeny derived from 6(3) X 15(1) and 100 X 6(3) crosses

Chickens from inbred line RPRL 6(3) are resistant to virally-induced Marek's disease (MD) and lymphoid leukosis (LL) and are relatively strong regressors of virally induced Rous sarcomas. Line 6(3) chickens are homozygous for three independent loci determining surface alloantigens of lymphocytes, Th-1 and Ly-4 on thymus-derived (T) cells and Bu-1 on bursa-derived (B) cells. In contrast, RPRL Lines 100 and 15(1) are highly susceptible to MD and LL and are weaker regressors of Rous sarcomas than 6(3). RPRL Lines 100 and 15(1) are homozygous for different alleles at the Th-1 and Ly-4 loci than 6(3), whereas only Line 100 differs from 6(3) at Bu-1. To test the possible association of these three antigen loci with variations in resistance to virally-induced tumors, homozygous genotypes among later generations derived from 6(3) X 15(1) and 100 X 6(3) crosses were identified by means of immunofluorescence testing of peripheral blood lymphocytes. Test progeny were then bred from matings of homozygous parents. No association was found between Rous sarcoma regression and the Th-1 and Ly-4 T cell alloantigen loci in F6 (6(3) X 15(1)) chickens, but the Bu-1 locus influenced rate of regression in F3 (100 X 6(3)) chickens. The Ly-4 in F6 (6(3) X 15(1)) and Bu-1 in the F3 (100 X 6(3)) chickens did not influence the incidence of LL. However, Th-1 influenced LL in F3 (100 X 6(3)) chickens (P less than .05) and possibly influenced LL in F6 (6(3) X 15(1)) chickens (P less than .09).

A small scale indirect 125iodine-labelled protein A binding assay for detection of monoclonal antibodies against avian oncoviral proteins

A small scale solid-phase radioimmunoassay employing 125I-labelled protein A is described which is suitable for screening large numbers of monoclonal antibodies directed against antigens which can be prepared in small amounts only, for example oncoviral proteins. The use of polystyrene Terasaki microtest plates instead of 96-well microtitre plates reduces the amount of antigen required for screening hybridoma supernatants to less than 30 ng/well. This method facilitates washing procedures and reduces the quantity of radioactive waste. The sensitivity and specificity of the method is demonstrated by the isolation and initial characterization of monoclonal antibodies specific for avian oncoviral transforming, structural and polymerase proteins.

Sarcoma growth in 15I5 x 7(2) chickens infected with avian sarcoma viruses of subgroup B or G

A comparative study was made of sarcoma growth in 15I5 x 7(2) chickens infected in the wing web at 4 weeks of age with strains of subgroup B or G avian sarcoma viruses. Infection with sarcoma viruses of either subgroup B or G resulted in the formation of progressive wing web sarcomas at the site of inoculation. The survival times of the subgroup G virus-infected chickens were generally at least twice as great as the survival times of the subgroup B virus-infected chickens, which averaged 6-9 weeks postinoculation. At 5 weeks postinfection, a significantly higher titer of virus neutralizing antibody was detected in the subgroup G virus-infected chickens. Necropsy indicated that a high percentage of subgroup B virus-infected chickens exhibited fibrosarcomas at sites distal to the primary wing web sarcomas, whereas only a small percentage of subgroup G virus-infected chickens exhibited distal sarcomas. The results further indicated that the viral env gene is a determinant of the pattern of distal sarcoma formation.

Antigenic and structural studies on the transforming proteins of Rous sarcoma virus and Yamaguchi 73 avian sarcoma virus

A widely cross reactive antiserum raised against denatured pp60v-src, the transforming protein encoded by Rous sarcoma virus, was used to test antigenic relationships with the transforming gene products encoded by other avian sarcoma viruses. The results showed that P90gag-yes, the transforming protein of a representative of Class III avian sarcoma viruses, is antigenically related to pp60v-src. Tryptic phosphopeptide analysis of P90gag-yes revealed two phosphotyrosine-containing peptides and one phosphoserine-containing peptide. One of the phosphotyrosine-containing peptides comigrated with the phosphotyrosine-containing tryptic peptide from pp60v-src.

Antibodies against a synthetic peptide of the avian retrovirus pp32 protein and the beta DNA polymerase subunit

Antibodies directed against a synthetic peptide (14 amino acids in length), whose amino acid sequence was predicted from the nucleotide sequence of the polymerase gene of Rous sarcoma virus (RSV), specifically immunoprecipitated the RSV beta polymerase subunit and the pp32 protein but not the alpha polymerase subunit. The first amino acid of the synthetic peptide is located approximately 30,800 Da from the predicted carboxyl terminus of the polymerase gene. These studies confirm the correct reading frame predicted for the polymerase gene and establish a minimal NH2 terminus for the pp32 DNA binding protein, which was previously shown to be derived from the carboxyl terminus of the polymerase gene.