Long non-coding RNA and MicroRNA profiling provides comprehensive insight into non-coding RNA involved host immune responses in ALV-J-infected chicken primary macrophage

Avian leukosis virus subgroup J (ALV-J) infection can cause tumors and immunosuppression in infected chickens. Macrophages play a crucial role in host defense against invading pathogens. In the present study, whole transcriptome analysis was performed to analyze the host factors including genes, microRNA (miRNA), long non-coding RNA (lncRNA) and their regulatory network in chicken primary monocyte-derived macrophages (MDMs). In total, 128 differentially expressed (DE) lncRNAs and 15 DE miRNAs were identified in MDMs at 3 h post infection (hpi), and 30 DE lncRNAs and 8 DE miRNAs were identified in MDMs at 36 hpi during ALV-J infection. We further constructed the DE lncRNAs-mRNAs, miRNA-mRNAs and lncRNAs-miRNA-mRNAs interaction networks. The results suggested that DE lncRNAs and miRNAs are involved in the regulation of CCND3 and SOCS5 in Jak-STAT signaling pathway via ceRNA network in ALV-J-infected MDMs at 3 hpi. In addition, lncRNAs including XLOC_672329, ALDBGALG0000001429, XLOC_016500 and ALDBGALG0000000253 cis-regulating CH25H, CISH, IL-1β and CD80 respectively in MDMs at 3 hpi participated in host antiviral responses. Our findings give a comprehensive view of the connection between non-coding RNA and ALV-J in chicken primary macrophages, and provide an excellent resource for further studies of epigenetic effects on ALV-J disease resistance breeding as well as immune system and genomic researches.

Avian leukosis virus subgroup - J as a contaminant in live commercially available poultry vaccines distributed in Nigeria

Globally, vaccines are used to prevent and control the menace of infectious diseases in livestock with some reported to be inadvertently contaminated with extraneous agents (EAs). With the aim of screening and characterizing for some selected EAs, 44 live viral poultry vaccines were randomly selected based on availability. The vaccines comprised 14 manufacturers in 10 different countries including Nigeria were screened by Polymerase Chain Reaction. In 9% (4/44) of the vaccines, contamination with only avian leukosis virus (ALV) subgroup J (ALV-J) was recorded. Other exogenous ALV subgroups, chicken infectious anemia and infectious laryngotracheitis viruses were absent. The EAs was found in infectious bursal disease (n = 1), Fowlpox (n = 2) and Mareks disease (n = 1) vaccines. Phylogenetic analysis of the ALV-J env gene showed clustering with contemporary group I and II. The result underscores the importance of screening vaccines to avoid the introduction and spread of EAs that could pose a threat to poultry production.

Precise gene editing of chicken Na+/H+ exchange type 1 (chNHE1) confers resistance to avian leukosis virus subgroup J (ALV-J)

Avian leukosis virus subgroup J (ALV-J), first isolated in the late 1980s, has caused economic losses to the poultry industry in many countries. As all chicken lines studied to date are susceptible to ALV infection, there is enormous interest in developing resistant chicken lines. The ALV-J receptor, chicken Na⁺/H⁺ exchange 1 (chNHE1) and the critical amino acid sequences involved in viral attachment and entry have already been characterized. However, there are no reported attempts to induce resistance to the virus by targeted genome modification of the receptor sequences. In an attempt to induce resistance to ALV-J infection, we used clustered regularly interspaced short palindromic repeats (CRISPR)-associated (CRISPR/Cas9)-based genome editing approaches to modify critical residues of the chNHE1 receptor in chicken cells. The susceptibility of the modified cell lines to ALV-J infection was examined using enhanced green fluorescent protein (EGFP)-expressing marker viruses. We showed that modifying the chNHE1 receptor by artificially generating a premature stop codon induced absolute resistance to viral infection, with mutations of the tryptophan residue at position 38 (Trp38) being very critical. Single-stranded oligodeoxynucleotide (ssODN)-mediated targeted recombination of the Trp38 region revealed that deletions involving the Trp38 residue were most effective in conferring resistance to ALV-J. Moreover, protein structure analysis of the chNHE1 receptor sequence suggested that its intrinsically disordered region undergoes local conformational changes through genetic alteration. Collectively, these results demonstrate that targeted mutations on chNHE1 alter the susceptibility to ALV-J and the technique is expected to contribute to develop disease-resistant chicken lines.

Discovery of novel long non-coding RNAs induced by subgroup J avian leukosis virus infection in chicken

Avian leukosis virus subgroup J (ALV-J) is an avian oncogenic retrovirus that has led to severe economic losses in the poultry industry in China in recent decades. Here, using high throughput transcriptome sequencing of HD11 and CEF cells infected with ALV-J, a set of 4804 novel long non-coding transcripts and numerous differentially expressed long non-coding RNAs (lncRNAs) were identified. We also found that they share relatively shorter transcripts and fewer exon numbers compared to mRNA. Correlation analysis suggested that many lncRNAs may activate gene expression in an enhancer-like manner other than through transcriptional regulation. Expression level analyses in vivo showed that three lncRNAs (NONGGAT001975.2, NONGGAT005832.2 and NONGGAT009792.2) may be associated with immune response regulation and could function as novel biomarkers for ALV-J infection. Our findings provides new insight into the pathological process of ALV-J infection and should serve as a high-quality resource for further research on epigenetic influences on disease-resistance breeding as well as immune system and genomic studies.

A recombinant avian leukosis virus subgroup j for directly monitoring viral infection and the selection of neutralizing antibodies

Avian leukosis virus subgroup J (ALV-J) has induced serious clinical outbreaks and has become a serious infectious disease of chickens in China. We describe here the creation of a recombinant ALV-J tagged with the enhanced green fluorescent protein (named rHPRS-103EGFP). We successfully utilize the rHPRS-103EGFP to visualize viral infection and for development of a simplified serum-neutralization test.

[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.

[The ALV-A/B specific antibodies correlation between ELISA and IFA detection in chicken serum]

To study the correlation between ELISA and IFA tests in detection of ALV-A/B antibody in chicken sera, ELSA S/P values and IFA titers for different serum samples were measured and statistically analyzed. The results indicated that there was a strong positive correlation between ELISA S/P values and IFA titers (r = 0.97435, P < 0.001). Because the positive correlation between ELISA and IFA was so strong and antibody positive rates were identical in two tests, it suggested that IFA could be used as a alternative method to replace ELISA kit when only limited numbers of samples to be tested to reduce the cost and increase the sensitivity.

[Mono-specific serum preparation and specificity of gp85 gene of subgroup A avian leukosis virus]

OBJECTIVE

In order to get a rapid specific diagnostic reagent for subgroup A Avian Leukosis Virus detection.

METHODS

The Avian Leukosis Virus Subgroup A (ALV-A) SDAU09E1 strain was inoculated into DF1 cells, an ALV-A- gp85 DNA fragment of 1023 bp was amplified from infected cells and inserted into PET-32a(+) plasmid at the location between restriction endonucleases BamH I and Not I sites. The recombinant plasmid PET-SDAU09E1 -gp85 was transformed into E coli. BL21 (Rosetta) for gp85 gene expression. Then we used the purified recombinant fusion protein to immunize 6 weeks old Kunming white mice, and the antiserum were prepared.

RESULTS

The recombinant ALV-A gp85 fusion protein with a molecular weight of 52.8 kDa demonstrated a good antigenecity. Mon-specific serum produced by vaccinated mice came out reactive with subgroups A and B ALV (ALV-A and ALV-B but not subgroup J ALV) by the indirect immunofluorescence (IFA) method.

CONCLUSION

This was the first time to demonstrate a mono-specific antiserum specific to ALV-A and ALV-B, it could be used for differential diagnosis of exogenous ALV infections in CEF cultures when in complement with ALV-J specific monoclonal antibodies. Chickens in our country are now distressed by both classic ALV-A/B and emerging ALV-J, making differential diagnosis necessary, so studying this reagent has high practical value.

Reduced serologic response to Newcastle disease virus in broiler chickens exposed to a Chinese field strain of subgroup J avian leukosis virus

In this study, a Chinese field strain of subgroup J avian leukosis virus (ALV-J), NX0101, was studied for its immunosuppressive effects in both commercial broilers and SPF white Leghorn chickens infected at 1 day of age. Our data demonstrated that NX0101 induced much more significant body and immune organ weight loss in the infected commercial broiler chickens in an earlier age than that in the SPF white Leghorn chickens. At the same time antibody responses to vaccinations of Newcastle disease virus (NDV) and infectious bursa disease virus (IBDV) in the NX0101-infected chickens were also evaluated and compared between the commercial broiler chickens and the SPF white Leghorn chickens. Compared with the control group of chickens, the hemagglutination inhibition (HI) antibody response to NDV vaccines was significantly reduced in the NX0101-infected commercial broiler chickens from as early as 20 days after vaccination. However, no significant difference in HI antibody response was seen when HI titers reached their peaks in the NX0101-inoculated and control SPF white Leghorn chickens, except it declined significantly faster in infected birds. Neither of these two types of chickens showed significant decrease of antibody response to IBDV vaccination. Herein, we conclude that this NX0101 strain of ALV-J could selectively suppress humoral immune reactions to NDV, especially in broilers. But challenge experiments were not conducted and, therefore, it cannot be known if decreased antibody levels correlated with decreased protection against NDV in this case.

Response of white leghorn chickens of various B haplotypes to infection at hatch with subgroup J avian leukosis virus

White leghorn chickens from seven 15.B congenic lines (genetically similar except for genes linked to the major histocompatibility complex [MHC] B haplotype) and two Line 0.B semicongenic lines were infected at hatch with strain ADOL Hc-1 of subgroup J avian leukosis virus (ALV-J). At 5, 8, 16, and 36 wk of age, chickens were tested for viremia, serum-neutralizing antibody, and cloacal shedding. Chickens were also monitored for development of neoplasia. In the 15.B congenic lines (B*2, B*5, B*12, B*13, B*15, B*19, and B*21) there were no significant differences in the incidence of viremia between B haplotypes. In fact, infection at hatch in all of the 15.B congenic lines induced tolerance to ALV-J because 100% of these chickens were viremic and transient circulating serum-neutralizing antibody was detected in only a few chickens throughout the 36 wk experiment. However, at 16 wk of age more B*15 chickens had antibody and fewer B*15 chickens shed virus than did the 16-wk-old B*2, B*5, or B*13 chickens. Moreover, compared with B*15 chickens, a higher percentage of B*13 chickens consistently shed virus from 8 wk postinfection to termination at 36 wk postinfection. The B haplotype had a transient effect on viral clearance in Line 0.B semicongenics, as more B*13 than B*21 chickens remained viremic through 5 wk of age. Very few (0%-18%) of the Line 0.B semicongenic chickens shed virus. By 36 wk of age, all Line 0 B*13 and B*21 chickens produced serum-neutralizing antibodies and cleared the virus. These results show that following ALV-J infection at hatch the immune response is influenced transiently by the B haplotype and strongly by the line of chicken. Although this study was not designed to study the effect of endogenous virus on ALV-J infection, the data suggest that endogenous virus expression reduced immunity to ALV-J in Line 15I5, compared with Line 0, a line known to lack endogenous virus genes.

Two different molecular defects in the Tva receptor gene explain the resistance of two tvar lines of chickens to infection by subgroup A avian sarcoma and leukosis viruses

The subgroup A to E avian sarcoma and leukosis viruses (ASLVs) are highly related and are thought to have evolved from a common ancestor. These viruses use distinct cell surface proteins as receptors to gain entry into avian cells. Chickens have evolved resistance to infection by the ASLVs. We have identified the mutations responsible for the block to virus entry in chicken lines resistant to infection by subgroup A ASLVs [ASLV(A)]. The tva genetic locus determines the susceptibility of chicken cells to ASLV(A) viruses. In quail, the ASLV(A) susceptibility allele tva(s) encodes two forms of the Tva receptor; these proteins are translated from alternatively spliced mRNAs. The normal cellular function of the Tva receptor is unknown; however, the extracellular domain contains a 40-amino-acid, cysteine-rich region that is homologous to the ligand binding region of the low-density lipoprotein receptor (LDLR) proteins. The chicken tva(s) cDNAs had not yet been fully characterized; we cloned the chicken tva cDNAs from two lines of subgroup A-susceptible chickens, line H6 and line 0. Two types of chicken tva(s) cDNAs were obtained. These cDNAs encode a longer and shorter form of the Tva receptor homologous to the Tva forms in quail. Two different defects were identified in cDNAs cloned from two different ASLV(A)-resistant inbred chickens, line C and line 7(2). Line C tva(r) contains a single base pair substitution, resulting in a cysteine-to-tryptophan change in the LDLR-like region of Tva. This mutation drastically reduces the binding affinity of Tva(R) for the ASLV(A) envelope glycoproteins. Line 7(2) tva(r2) contains a 4-bp insertion in exon 1 that causes a change in the reading frame, which blocks expression of the Tva receptor.

Assessing the roles of endogenous retrovirus EAV-HP in avian leukosis virus subgroup J emergence and tolerance

Avian leukosis virus (ALV) subgroup J is thought to have emerged through a recombination event between an unknown exogenous ALV and the endogenous retrovirus elements designated EAV-HP. All EAV-HP elements identified to date in the chicken genome show large deletions, including that of the entire pol gene. Here we report the identification of four segregating chicken EAV-HP proviruses with complete pol genes, one of which shows exceptionally high sequence identity and a close phylogenetic relationship with ALV-J with respect to the env gene. Embryonic expression of EAV-HP env has been suggested as a factor associated with immunological tolerance induction in a proportion of ALV-J-infected meat-type chickens. In support of this, env gene transcripts expressed from two of the four newly identified EAV-HP proviruses were demonstrated in chicken embryos. However, when ALV-J-infected outbred meat-type chickens were assessed, the presence of intact EAV-HP proviruses failed to directly correlate with ALV-J tolerance. This association was further examined using F(2) progeny of two inbred lines of layer chicken that differed in EAV-HP status and immunological responses to ALV-J. Immunological tolerance developed in a small proportion of F(2) progeny birds, reflecting the expected phenotypic ratio for inheritance of a double-recessive genotype; however, the status of tolerance did not show any direct correlation with the presence of the intact EAV-HP sequence. Nevertheless, identification of an intact chicken EAV-HP locus showing a uniquely close relationship to the ALV-J prototype clone HPRS-103 in the env region provides the strongest evidence of its contribution to the emergence of ALV-J by recombination.

Response of white leghorn chickens of various genetic lines to infection with avian leukosis virus subgroup J

In Experiment 1, chickens from various white leghorn experimental lines were inoculated with strain ADOL-Hcl of subgroup J avian leukosis virus (ALV-J) either as embryos or at 1 day of age. At various ages, chickens were tested for ALV-J induced viremia, antibody, and packed cell volume (PCV). Also, at 4 and 10 wk of age, bursal tissues were examined for avian leukosis virus (ALV)-induced preneoplastic lesions with the methyl green-pyronine (MGP) stain. In Experiment 2, chickens harboring or lacking endogenous virus 21 (EV21) were inoculated with strain ADOL-Hcl of ALV-J at hatch. All embryo-inoculated chickens in Experiment 1 tested positive for ALV-J and lacked antibody throughout the experimental period of 30 wk and were considered viremic tolerant, regardless of line of chickens. By 10 wk of age, the incidence of ALV-J viremia in chickens inoculated with virus at hatch varied from 0 (line 0 chickens) to 97% (line 1515); no influence of ALV-J infection was noted on PCV. Results from microscopic examination of MGP-stained bursal tissues indicate that ALV-J can induce typical ALV-induced transformation in bursal follicles of white leghorn chickens. Lymphoid leukosis and hemangiomas were the most common ALV-J-induced tumors noted in chickens in Experiment 1. At termination of Experiment 2 (31 wk of age), 54% of chickens harboring EV21 were viremic tolerant compared with 5% of chickens lacking EV21 after inoculation with ALV-J at hatch. The data indicate that genetic differences among lines of white leghorn chickens, including the presence or absence of EV21, can influence response of chickens to infection with ALV-J.

The effects of cyclophosphamide treatment on the pathogenesis of subgroup J avian leukosis virus (ALV-J) infection in broiler chickens with Marek's disease virus exposure

Studies were performed to determine the effects of Bcell suppression on the pathogenesis of Subgroup J avian leukosis virus (ALV-J) in broiler chickens. Neonatal chickens were treated with cyclophosphamide (CY) or PBS, and then infected with ALV-J (ADOL-7501) at 2 weeks of age. CY treatment induced B cell specific immunosuppression throughout the experiment confirmed by decreased bursal weight, intact lymphocyte mitogenetic activity stimulated by Con A and increased relative subpopulation of CD3-positive cells as measured by flow cytometry. Chickens in this experiment had Mareks disease virus exposure prior to three weeks of age as determined by the presence of lymphocytic infiltration and antibody. Virus neutralizing antibody against ALV-J was first observed at 6 weeks post-infection in some of the infected chickens in the PBS group. As expected, none of the chickens from the CY group and uninfected chickens developed virus-neutralizing antibody. The viremic status was measured by real time RT-PCR using SYBR green I dye. The percentage of viremic chickens was significantly higher, and more chickens had high titered viremia, in the CY treated group. No neoplastic foci consistent with ALVJ infection were observed in any of the experimental chickens. The frequency and intensity of viral antigen expression determined by immunohistochemistry was significantly higher in tissues from CY treated birds than those of PBS treated chickens at 3 weeks post-infection. This study showed that B cell specific immunosuppression with CY treatment in chickens resulted in increase in viremia and viral antigen load in tissues.

Effects of cyclosporin A treatment on the pathogenesis of avian leukosis virus subgroup J infection in broiler chickens with Marek's disease virus exposure

In this study, we investigated the effects of T-cell suppression on the pathogenesis of subgroup J avian leukosis virus (ALV-J). Chickens were treated with cyclosporin A (CSP) 50 mg/Kg body weight or a corresponding volume of olive oil per every three days after hatching until the end of experiment. Some of the chickens from each treatment group were infected with an isolate of ALV-J, ADOL-7501, at 2 weeks of age. The effects of viral infection were compared to uninfected birds in same treatment group. Intramuscular injection of CSP induced significant T-cell specific immunosuppression determined by decreased cutaneous basophilic hypersensitivity response and decreased lymphocyte mitogenic activity using concanavalin A. Most of the chickens examined had Marek's disease virus infection prior to 3 weeks of age. The percentage of antibody-positive birds and antibody titers were similar in infected chickens between both treatment groups. The ratio of viremic chickens was significantly higher in CSP treated group than that of the Oil treated group. Microscopically, one CSP treated chicken had a nephroblastoma at 10 weeks post infection. At 7 and 10 weeks post-infection, more chickens had myeloid cell infiltrations in multiple organs including heart, liver and occasionally lung. Expression of ALV-J viral antigen determined by immunohistochemical staining was significantly higher in CSP treated chickens than Oil treated chickens at 10 weeks post-infection. This study indicated that chemically-induced T-cell suppression may enhance pathogenicity of the AVL-J virus in broilers.

Pathogenicity of two recombinant avian leukosis viruses

We have recently described the isolation and molecular characteristics of two recombinant avian leukosis subgroup J viruses (ALV J) with an avian leukosis virus subgroup A envelope (r5701A and r6803A). In the present study, we examined the role of the subgroup A envelope in the pathogenesis of these recombinant viruses. Chickens of line 151(5) x 7(1) were inoculated at 1 day of age with r5701A, r6803A, Rous-associated virus type 1 (RAV-1), or strain ADOL-Hcl of ALV-J. At 2, 4, 10, 18, and 32 wk postinoculation (PI), chickens were tested for avian leukosis virus (ALV)-induced viremia, shedding, and neutralizing antibodies. All except one chicken inoculated with the recombinant viruses (98%) developed neutralizing antibodies by 10 wk PI compared with only 16% and 46% of the ADOL-Hcl and RAV-1-inoculated birds, respectively. ALV-induced tumors and mortality in the two groups inoculated with recombinant viruses were different. The incidence of tumors in groups inoculated with r5701A or RAV-1 was 100% compared with only 9% in the groups inoculated with r6803A or ADOL-Hcl. The data suggest that differences in pathogenicity between the two recombinant viruses might be due to differences in the sequence of the 3' untranslated region (presence or absence of the E element), and, therefore, not only the envelope but also other elements of the viral genome play an important role in the pathogenesis of ALV.

Serologic Profiles of Chickens Infected with Subgroup J Avian Leukosis Virus

Subgroup J avian leukosis virus (ALV-J) causes serious economic losses in the commercial poultry industry. Measuring group-specific antigen (GSA) by enzyme-linked immunosorbent assay (ELISA) has been used to identify chickens infected with this virus. However, the inability of ELISA to discriminate the GSA from endogenous ALV (subgroup E ALV [ALV-E]) or ALV-J infection has limited its usage. The purpose of the present study was to develop a method to discriminate between uninfected flocks having ALV-E and ALV-J-infected flocks by ELISA. The GSA and anti-ALV-J antibody in the plasma samples from chickens at different ages in three grandparent farms were measured by ELISA. Infected flocks were confirmed by reverse transcription-polymerase chain reaction with different subgroup-specific primers and sequence analysis. The results indicated that the GSA of ALV-J-infected flocks increased, but that of the uninfected flocks decreased during young ages. The anti-ALV-J antibody of infected flocks was higher and increased earlier than that of uninfected flocks. Thus, measuring GSA in blood at the ages of 1 and 6 wk by ELISA is suitable to discriminate between ALV-J-infected flocks and uninfected flocks having ALV-E.

Effect of an in ovo infection with a Dutch avian leukosis virus subgroup J isolate on the growth and immunological performance of SPF broiler chickens

The effect of an in ovo infection with a Dutch isolate of avian leukosis virus subgroup J (ALV-J) on the growth of specific pathogen free (SPF) broiler chickens was analysed. During this study, possible immune suppressive effects of ALV-J were assessed by measuring delayed-type hypersensitivity with keyhole limpet haemocyanin (KLH), natural killer (NK) cell activity, the production of radicals of nitric oxide (NO) by macrophages, humoral immune response against Newcastle and infectious bursal disease vaccine viruses, and automated total and differential leukocyte counts. In an attempt to elucidate the underlying causal mechanisms of the induced growth retardation, 3,3',5-triiodothyronine (T3) concentrations in serum were measured. Four experiments were conducted. In experiment 1, ALV-J-injected birds were compared with ALV subgroup A (ALV-A)-injected and negative control chickens. In experiment 2, ALV-J-injected birds were only compared with negative controls. Finally, in experiments 3a and 3b, ALV-J-injected chickens were compared with negative controls and a group of chickens in which only 10% of birds had been injected with ALV-J. Birds were injected in ovo at day 7 of incubation with 10(4) median tissue culture infectious dose (TCID(50)) ALV-J or ALV-A, except in experiment 3a where 10(2) TCID(50) ALV-J was injected. Significant growth suppression was found in all 100% of ALV-J-infected groups. The average growth retardation of ALV-J-infected birds compared with negative controls at 6 weeks of age was approximately 8, 11, 2.5 and 6% for the four successive experiments performed. The delayed-type hypersensitivity test against KLH of ALV-J-infected birds showed a tendency towards lower wattle thickness; however, the difference with controls was not significant (P > 0.05). The same was true for NK cell activity and NO production by macrophages, although the difference was not significant. The total and differential leukocyte counts performed on blood samples from birds at 3, 4 and 6 weeks of age as well as the humoral immune response against Newcastle and infectious bursal disease vaccine viruses did not show significant differences between treatment groups either. Only the number of basophils were significantly higher (P = 0.02) in ALV-J-infected birds at 3 weeks of age. No significant lower T(3) levels were found in ALV-J-infected birds in weeks 2 and 3 (experiment 2) and weeks 3 and 5 (experiment 3b); however, at 4 weeks (experiment 2) and 6 weeks (experiment 3b) of age, T(3) levels were significantly lower suggesting mild hypothyroidism in these broilers. In conclusion, the present experiments show the occurrence of significant growth retardation in SPF broilers after an ALV-J in ovo infection. The various studies performed to assess the immune competence of ALV-J-infected chickens did not show significant differences in immune responsiveness. The assays on cellular immunity showed a tendency to a lower response in ALV-J-infected birds, but these differences were not statistically significant.

Immunohistochemical localization of avian leukosis virus subgroup J in tissues from naturally infected chickens

The tissue tropism of avian leukosis virus (ALV) subgroup J (ALV-J) was investigated in congenitally infected broiler chickens by an immunohistochemistry technique detecting gp85 viral glycoprotein. All organs examined contained detectable antigen. The most intense staining was in the adrenal gland, heart, kidney, and proventriculus. Intense staining for viral antigen in the heart may explain the ability of ALVs to cause cardiomyopathy. Although recent investigations failed to demonstrate specific viral staining in bone marrow from infected chickens, we were able to show moderate staining in myelocytic precursor cells in bone marrow. This finding agrees with previous work showing cell cultures of bone marrow are susceptible to ALV-J infection and the tendency of subgroup J to predominantly induce myeloid rather than lymphoid neoplasms.

Development and characterization of monoclonal antibodies to subgroup J avian leukosis virus

In an attempt to develop a specific diagnostic test for avian leukosis virus (ALV) subgroup J (ALV-J) strain Hc1, four monoclonal antibodies (MAbs), JE9, G2, 145, and J47, were generated that are specific for ALV-J envelope glycoprotein, gp85. Polymerase chain reaction (PCR) was used to amplify genomic pro-viral DNA of Avian Disease and Oncology Laboratory (ADOL)-Hc1 and ADOL-4817 envelope genes. Both open reading frames encoding glycoproteins gp85 and gp37 were cloned into baculoviruses. Abundant expression of gp85 and gp37 was detected in the recombinant viruses with specific antibody to Hc1 strain of the ALV-J. The expressed proteins were used for immunization of mice to produce hybridoma cell lines secreting MAbs specific to ALV-J envelope protein. A panel of MAbs was generated by fusing NS1 myeloma cells and spleen cells from mice immunized with the recombinant baculoviruses. With the use of an immunofluorescence assay, three MAbs (JE9, G2, 145) reacted with ALV-J but not with subgroups A, B, C, D, or E of ALV. MAb J47 reacted with all exogenous subgroups of ALV including A, B, C, D, and J but not with endogenous subgroup E viruses. Western blot analysis was performed with all four MAbs against recombinant baculovirus and Hc1-infected chicken embryo fibroblast (CEF) lysates. A major band with a molecular weight about 90 kD corresponding to the size of ALV-J envelope was consistently obtained. With these MAbs, we detected the Hc1 antigen in CEFs infected with several ALV-J viruses isolated in the United States and also in tissue sections from chickens infected with Hc1 strain of ALV-J. These MAbs will be useful reagents for the diagnosis of ALV-J infection because they recognize a common antigenic epitope in six isolates tested thus far.

Heterophil function and resistance to staphylococcal challenge in broiler chickens naturally infected with avian leukosis virus subgroup J

Avian leukosis virus subgroup J has a high tropism for myeloid lineage cells and frequently induces neoplastic transformation of myelocytes. The impact of congenital avian leukosis virus subgroup J infection on the function of circulating heterophils and susceptibility to staphylococcal infection was investigated. Six-week-old broiler chickens negative for exogenous avian leukosis viruses or congenitally infected with avian leukosis virus subgroup J were inoculated intravenously with 10(6) colony-forming units of Staphylococcus aureus, and pre- and postinoculation heterophil function was assessed. All chickens developed a leukocytosis with heterophilia after inoculation, but total leukocyte and heterophil counts were significantly higher in leukosis-negative chickens than in virus-infected chickens. Tenosynovitis was more severe in leukosis-negative chickens, and 2/10 (20%) of the virus-infected chickens had no histologic evidence of tenosynovitis. Osteomyelitis in the tibiotarsus or tarsometatarsus developed in 5/10 (50%) of the chickens in each group. S. aureus was recovered from the hock joint of 6/10 (60%) of the chickens in each group. Heterophils from all chickens exhibited similar phagocytic ability pre- and postinoculation. Heterophils from virus-infected chickens exhibited less bactericidal ability preinoculation than did heterophils from leukosis-negative chickens. However, postinoculation bactericidal ability was similar in both groups. Avian leukosis virus subgroup J provirus was present in heterophils isolated from congenitally infected chickens. Heterophils isolated from broiler chickens congenitally infected with avian leukosis virus subgroup J exhibit no significant functional deficits, and infected and uninfected chickens exhibit similar susceptibility to staphylococcal infection.

Resistance to Marek's disease virus in White Leghorn chickens: effects of avian leukosis virus infection genotype, reciprocal mating, and major histocompatibility complex

Genetic improvement for resistance to Marek's Disease (MD) in chickens continues to be of interest to the poultry industry. The aims of this study were to identify effects of the MHC on the molecular level and of avian leukosis virus (ALV) resistance status on MD mortality in two noninbred White Leghorn chicken lines that differ in B blood group type. Previously, within each of the chicken lines, sublines had been selected for resistance or susceptibility to ALV infection with Subgroups A and B. In this study, F2 offspring, obtained by crossing the two ALV-resistant or the two ALV-susceptible sublines, were tested for MD mortality after contact exposure at 1 d of age. Reciprocal matings were made in the grandparental generation. The MD mortality percentages, in an observation period of 17 wk, of F2 offspring from two hatches were 82.63 and 92.35%, respectively. Survival analysis (Cox model) was applied to assess the risk of dying from MD. No differences in MD mortality risk profiles were found between ALV-resistant and ALV-susceptible F2 offspring. Within ALV-susceptible F2 offspring, however, a reciprocal mating effect was observed in both hatches. The MHC Class I, II, and IV restriction fragment length polymorphism (RFLP) analyses were carried out on birds of the first hatch. Although two of 11 MHC class IV RFLP bands displayed a significant effect, in general, a strong association of MHC and MD mortality was not detectable.

Proviral load and expression of avian leukosis viruses of subgroup C in long-term persistently infected heterologous hosts (ducks)

Proviral DNA load and expression of avian leukosis viruses of subgroup C (ALV-C) in ducks infected in mid embryogenesis were studied using quantitative PCR, RT-PCR, in situ hybridization employing ALV-specific riboprobe, and immunohistochemistry. A group of long-term surviving, non-reviremic ducks was selected for the study and compared to control reviremic animals in order to obtain information about persisting retroviruses in different duck tissues. A widespread distribution of proviruses in the tested tissues was found, but the proviral load was significantly lower in non-reviremic in comparison to reviremic animals. The only exception were brain and blood cells, in which no significant difference in the quantity of integrated proviruses was found between both categories of ducks, thus indicating an exceptional position of the brain and blood cells among all tested tissues. Contrary to reviremic, the proviruses were not transcribed in non-reviremic ducks, with the exception of brain and thymus. In the majority of non-reviremic ducks viral RNA was revealed in the brain, but no infectious virus could be recovered from this tissue. The opposite situation was observed in the thymus, where infectious virus was recovered but viral RNA remained below the detection limit of the assay. As revealed by in situ analysis, infected cells were either disseminated or focally distributed in tissues. From the long-term follow up of ALV-C in intraembryonally infected ducks we conclude that this model is suitable for the study of retrovirus persistence accompained both by the presence and absence of reviremias. The possible consequences of transmission and long-term persistence of retroviruses in the heterologous host for retroviral evolution are discussed.

Dynamics of protein 27 of avian leukosis virus and transforming growth factor beta2 in lymphoid leukosis susceptible and resistant broiler chicken breeding stock

The dynamics of the serum concentration of protein 27 (P27) of avian leukosis virus and transforming growth factor beta2 (TGF-beta2) were compared during the period between 29 and 59 weeks of age in two flocks of broiler chicken breeding stock undergoing outbreaks of severe lymphoid leukosis (LL) associated with persistent high mortality (susceptible) and in another two flocks of breeding stock with the presence of avian leukosis virus in association with low mortality due to LL (resistant). The average mean concentration of serum P27 in the LL-susceptible flocks was significantly higher (p<0.05) than that in the LL-resistant flocks in six out of seven samplings performed at 5-week intervals, between 29 and 59 weeks of age. The peak in the average rise of serum P27 in the LL-resistant flocks (309 pg/ml) was associated with the highest level of TGF-beta2 (1282 pg/ml) among all flocks and at all sampling times. The significance of TGF-beta2 in inhibition of lymphoid tumour development is discussed.

Response of chickens carrying germline insert ALVA11 to challenge with a field strain of subgroup A avian leukosis virus

The ALVA11 germline insert in chickens is a defective subgroup A avian leukosis virus (ALV) proviral insert that expresses a low-to-moderate level of subgroup A ALV envelope glycoprotein. Chicks carrying or lacking ALVA11 were evaluated for response to challenge by RPL-42, a pathogenic field strain of subgroup A ALV, by either exposure to chicks shedding RPL-42 or direct injection with various doses of RPL-42. Chicks carrying ALVA11 were significantly more resistant, as measured by infectious virus and viral antibody status, to horizontal infection and direct injection of RPL-42 than chicks lacking ALVA11.

Chicken industry strategies for control of tumor virus infections

Marek's disease (MD) and lymphoid leukosis (LL) are two distinct viral diseases that cause tumor mortality in chickens. Marek's disease, being horizontally transmitted, is controlled through biosecurity measures and vaccination. Prevention of early exposure before vaccine immunity is established is most important. Some multi-house growing farms have converted to all single-age placements to break the ongoing cycle of transmission. Vaccination against MD involves either in ovo or day-old administration of live vaccine, including single or multiple serotype products. Field viruses appear to adapt over time and become resistant to the prevalent vaccine. The Rispens vaccine (CVI-988) has shown good efficacy against recently emerging very virulent MD strains in the U.S. Genetic resistance of the host to MD and control of other immunosuppressive diseases also affects MD susceptibility. Lymphoid leukosis is primarily vertically transmitted and therefore controlled by elimination of shedder hens at the primary breeder level. Depending upon the genetic type, commercial performance of laying hens may be greatly improved by eradication of the LL virus from the breeding stock.

Genetic resistance to avian viruses

Viral infections of poultry can be catastrophic in terms of both welfare and economics, and although vaccines have been very successful in combating these diseases, new forms of viruses have evolved which present increasing difficulties for vaccine control. Differences in genetic susceptibility are known to exist for many of the major viral pathogens of poultry. Consequently, an increase in the level of genetic resistance provides a possible means of enhancing protection of flocks. This is particularly feasible where specific resistance genes have been identified, as in the case of avian leukosis and Marek's disease, and the development of genetic maps of the chicken has offered new possibilities for the identification of further resistance genes. It has also become clear that there are genetic differences in the response to live attenuated vaccine viruses, and new possibilities exist to manipulate the genetics of host flocks so that the effect of vaccination can be optimised.

Some chickens which are viraemic with subgroup J avian leukosis virus have antibody-forming cells but no circulating antibody

New immunoperoxidase-based assays for splenic IgG -antibody-forming cells (AFC) and serum IgG-antibody were used to look for antibody to HPRS-103 in meat-type birds. Meat type birds are known to be less likely to produce neutralising antibody and to be less likely to clear virus from their serum than layer-type birds after infection at hatch. In this work all 12 of the brown leghorn layer-type birds and 5/12 of the line 21 meat-type birds had produced AFC and serum antibody and had cleared serum virus at 63, 82 and 110 days of age. None of the seven viraemic line 21 birds contained serum antibody but three produced AFC. The four viraemic line 21 birds which lacked AFC occurred later in the experiment and had a higher level of virus than the three viraemic line 21 birds which possessed AFC. This suggests that most line 21 birds do not control HPRS-103 and eventually become anergic.

Recombinant env-gp85 of HPRS-103 (subgroup J) avian leukosis virus: antigenic characteristics and usefulness as a diagnostic reagent

We describe the construction of a recombinant baculovirus containing the cloned DNA encoding the gp85 envelope glycoprotein of HPRS-103 (subgroup J) avian leukosis virus fused to the carboxy-terminus of the affinity tag glutathione-S-transferase. The fusion protein was efficiently secreted into the supernatant medium of the infected insect cell culture and could be purified in a single step using immobilized glutathione. An enzyme-linked immunosorbent assay using the recombinant protein was found to be specific and sensitive for detection of HPRS-103 virus-specific antibodies in the sera of infected birds.

Viral diseases of the immune system and strategies to control infectious bursal disease by vaccination

Viral infections which are immunosuppressive can affect the economics of poultry production, often as a result of the chicken's increased susceptibility to secondary infections and sub-optimal response to vaccinations. The mechanism of this immunosuppression has been studied in detail for certain chicken viruses. The replicating virus can have both direct and indirect effects on the cells of the immune system. The special role of the bursa of Fabricius, as a lympho-epithelial organ, will be mentioned. The effects of oncogenic viruses (MDV, REV and ALV) on the immune system will be discussed as will the present status of our knowledge on the immunosuppressive effects of certain respiratory viruses such as ILT, NDV and reovirus. Two major immunosuppressive agents are CAV and IBDV. The effects of IBDV will be described in more detail because of its economic importance. Advances made in the molecular biology of both the virus and the immune system give new opportunities to control the disease by vaccination. Successful vaccination strategies applied in the past and options for the future will be discussed.

Intratesticular inoculation of avian leukosis virus (ALV) in chickens--production of neutralizing antibodies and lack of virus shedding into semen

In order to investigate the possibility of producing transgenic chickens by injection of avian leukosis virus-based vectors into testis, we have analyzed the infection rate of testicular cells following inoculation of Rous-associated virus type 1 (RAV-1) into the gonads of adult and 1-wk-old brown leghorn males. Viroproduction, neutralizing antibody production, and vital DNA presence in testis, blood, muscle, and semen were analyzed at various times after infection. Inoculation of RAV-1 into the gonads of adult males resulted in a low level of viroproduction in testis and blood, followed by the appearance of neutralizing antibody 2 or 3 wk later. Neither viroproduction in semen nor viral DNA presence in sperm were detected even though the infected chickens were found to produce RAV-1 in testis. One week after intratesticular inoculation of 1-wk-old males with RAV-1, a high level of viroproduction was found in blood and testis, and viral DNA was detected in gonadal cells. Further, by 6 wk after inoculation, the production of virus decreased in all tissues, viral DNA could not longer be detected in the testis, and neutralizing antibodies appeared in blood. All together these data show that it is possible to infect testicular cells by direct inoculation of RAV-1 in the testis, and that the immune response of both adult and young chickens seems to reduce this infection. Moreover, no evidence of spermatozoa infection was found; this result suggests that RAV-1 inoculation into testis may not induce genetic transmission of virus, and consequently would not be useful in the production of transgenic chickens.

Lymphoid leukosis viruses, their recognition as 'persistent' viruses and comparisons with certain other retroviruses of veterinary importance

Diseases caused by lymphoid leukosis virus (LLV), a retrovirus, take a long time after infection to develop and have a wide variety of pathological manifestations. This long latent period is characteristic of 'persistent virus infections'. Disease produced by LLV infection and its underlying mechanisms is compared with 'persistent' infections caused by other retroviruses in birds and mammals of veterinary importance. The diseases considered for comparison are those caused by reticuloendotheliosis, feline leukaemia, bovine leukosis and equine infectious anaemia viruses. There are significant changes in the immunological status in all diseases caused by these viruses. LLV infections follow this trend with, in manifestations of neoplastic disease, a perturbation of the normal switch that occurs from IgM to IgG synthesis. There are also indications of other immunological disturbances. Factors other than immunological disturbances may contribute to the length of time after infection required for the many forms of LLV infection to appear. Such additional factors may include the operation of 'biological clocks', such as the arrival of sexual maturity, and also the very nature of retroviruses. These factors, like the immunological changes, play major roles in the maintenance and progression of persistent retrovirus infections.

Effect of serotype 2 and 3 Marek's disease vaccines on the development of avian leukosis virus-induced pre-neoplastic bursal follicles

The effect of serotype 2 and 3 Marek's disease virus (MDV) vaccines on the development of pre-neoplastic bursal lesions induced by two strains of subgroup A avian leukosis virus (ALV) was studied. Chickens of line 15I5 x 7(1) susceptible to ALV-induced lymphoma were inoculated at hatch with Rous-associated virus-1 (RAV-1) or strain RPL-40 of subgroup A ALV. All chickens, except for negative controls, were also inoculated at hatch with strain 301B/1 of serotype 2 MDV or strain FC126 of turkey herpesvirus (HVT), a serotype 3 MDV. At 11 and 14 weeks of age, serial sections of bursal tissues from chickens in various treatment groups were stained with methyl green pyronin and examined for ALV-induced pre-neoplastic bursal lesions, also known as hyperplastic follicles. At 6 days and at 11 and 14 weeks of age, bursal tissues from groups of chickens inoculated with serotype 2 MDV and ALV at hatch were also examined for the presence of MDV genome by in situ hybridization. The number of ALV-induced hyperplastic follicles was significantly higher in chickens inoculated with serotype 2 MDV than in unvaccinated chickens or in chickens vaccinated with HVT. In contrast, the lowest number of hyperplastic follicles was noted in chickens vaccinated with HVT, regardless of strain of ALV used. These results suggest that enhancement of lymphoid leukosis may result from an increase in the number of ALV-induced hyperplastic follicles caused by the MDV and also that the enhancing effect of MDV on ALV-induced lymphomagenesis may occur at the stage of formation of hyperplastic follicles in the bursa.

A recombinant fowlpox virus expressing the envelope antigen of subgroup A avian leukosis/sarcoma virus

A recombinant fowlpox virus (FPV) was constructed by inserting cloned sequences from Schmidt-Ruppin subgroup A avian sarcoma virus coding for the viral envelope (env) antigen into a nonessential region of FPV DNA downstream from a synthetic promoter. Sera from chickens hyperimmunized with the recombinant FPV neutralized the infectivity of the homologous subgroup A virus (RCASBP/AP) but only weakly neutralized the infectivity of Rous sarcoma virus, another subgroup A avian leukosis virus. Similarly, vaccination of 1-day-old chicks with this recombinant FPV protected against infection with RCASBP/AP virus but not against infection with another subgroup A Rous-associated virus (RAV-1). These results show that such a recombinant FPV can be used to protect chickens against avian leukosis virus and confirm previous observations that a type-specific antigenic variability existed within the subgroup A avian leukosis/sarcoma virus group.

Influence of the alv6 recombinant avian leukosis virus transgene on production traits and infection with avian tumor viruses in chickens

The biological costs of the alv6 recombinant transgene that in chickens induces dominant resistance to the subgroup A avian leukosis virus (ALV), in terms of effects on production traits, were studied. Four generations of White Leghorn chickens of Line TR, segregating for alv6 but free of endogenous viral genes, as well as two generations of crosses between TR and Ottawa Line WG (WGTR) were tested under a specific-pathogen-free environment. In the birds studied, the transgene appeared unchanged compared to the original alv6: No major changes in alv6 DNA were detected by restriction analysis, the transgene did not express the group-specific antigen of ALV, and its presence was associated with absence of immune response to ALV. In most test years, and both TR and WGTR genomic backgrounds, alv6 was associated with delayed sexual maturity by 4 to 6 d, reduced egg production to 497 d of age by 20 to 46 eggs, and a 3.6 to 15% decline in egg production rate. No consistent effects on other traits, including mortality, were detected. When inoculated with the AC-1 isolate of Marek's disease virus in a separate experiment, TR birds with alv6 had a significantly lower body weight gain to 10 d of age than their sibs without the transgene. Thus, transgenesis has biological costs that have to be assessed against desirable effects of transgenes.

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.

Retrovirus-induced B cell neoplasia in the bursa of Fabricius

The chicken bursa provides a revealing experimental model system which has helped unravel some of the mysteries surrounding induction of neoplasia by retroviruses lacking dominant viral oncogenes. Analysis of this system continues to provide opportunities for further insight into mechanisms underlying some of the essential characteristics of neoplastic change including maturation arrest, prolonged cell survival, and genetic instability. The deregulation of c-myc expression induced by nearby proviral integration appears to initiate preneoplastic change in a specific window of development, i.e., the bursal stem cell. The generation of large numbers of these preneoplastic stem cells, and the ability for further amplification by transplantation technology, may provide an opportunity to address questions such as how and why myc oncogenes produce preneoplastic maturation arrest or why stem cells are selective targets for these effects. Among the unexplained consequences of this preneoplastic state appears to be genetic instability which leads, inevitably, to formation of invasive bursal neoplasms. It is at least conceivable that the observed myc-induced enhancement of the remarkable capacity for apoptotic cell death present in bursal cells plays a role in this instability. DNA strand breakage is a very early feature of bursal cell apoptosis. If such breakage could occur in sublethal form it might provide a mechanism for increased frequency of genetic change (deletions, rearrangement, and recombination). Among the changes that seem required for successful tumor cell growth outside of follicles is the suppression of cell death induced by loss of cell-cell contact which is characteristic of normal and preneoplastic bursal cells. Several genes in the bcl-2 family are potentially important in the modulation of cell death events central to the evolution of these neoplasms. Their role, if any, remains to be established.

Synergism between the endogenous viral loci ev6 and ev9 in inducing immunological tolerance to avian leukosis virus

1. The course of infection by exogenous avian leukosis virus was followed in a commercial strain of White Leghorn domestic fowls by measuring viral antigen in feather pulp and egg albumin. Ten days after hatching, 2 out of 360 birds tested positive and at 286 days of age about 60% of the birds had been antigen positive at least once. 2. Among the antigen positive birds, two groups could be distinguished: those which permanently and those which transiently expressed viral antigen. Permanent antigen expression was associated with low antibody titres, while transient antigen expression was associated with high antibody titres. 3. The strain segregated for the two endogenous viral genes ev6 and ev9, both of which express endogenous viral envelope protein, and have been implicated in affecting immune-responsiveness. The antibody titre in individuals positive for both ev6 and ev9, was significantly lower than in those which had none or only one of the two ev-genes. In addition, individuals positive for both ev-genes occurred more frequently in the group permanently positive for viral antigen than in the group transiently antigen positive. 4. The results indicate that there was a strong synergism between ev6 and ev9 in reducing the antibody response to exogenous avian leukosis virus infection, perhaps by inducing immune tolerance or interfering with antibody formation.

Genetic control of cellular infection by subgroups A and C RNA tumour viruses in guinea fowl

An investigation was carried out in guinea fowl to determine their susceptibility to infection by Rous sarcoma viruses of subgroups A and C. A standard dose of each subgroup virus was inoculated into 14-day-old embryos via the chorioallantoic membrane (CAM). On the 10th day after inoculation, 50% of the embryonic chorioallantoic membranes were harvested to assess their infection status (CAM(+) or (-)), while the rest were allowed to hatch. The hatchabilities of the embryos inoculated with subgroups A and C were about 50% and 57%, respectively. The relative sensitivities of guinea fowl to infection by viruses of subgroups A and C were observed to be 0.220 and 0.003, respectively, as compared to chickens (1.00). Mortality due to subgroup A virus-induced liver tumours (LT) was 54% and four phenotypic subclasses, namely CAM(+) LT(+), CAM(+) LT(-), CAM(-) LT(+) and CAM(-) LT(-), were observed in guinea fowl as in chickens. However, a higher incidence (31%) of conversely associated phenotypes, i.e. CAM(+) LT(-) and CAM(-) LT(+), were observed in guinea fowl. Mortality caused by subgroup A virus-induced liver tumours was first observed in inoculated guinea fowl keets during the 3rd week after hatching, and 93% of the mortality occurred within 6 weeks. The peak mortality occurred in the 4th week after hatching. The target organs for transformation were considered to be the liver and spleen because of the equal incidence of tumours in these organs. Males and females were equally likely to die from liver tumours.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of ev6 on the immune response to avian leukosis virus infection in rapid-feathering progeny of slow- and rapid-feathering dams

Endogenous virus (EV) locus ev6 encodes only virus envelope glycoprotein. The influence of ev6 on the immune response to contact infection with hatchmates infected with avian leukosis virus (ALV) was compared in replicate hatches. The ALV Subgroup E-resistant, rapid-feathering (RF) female chickens produced by slow-feathering (SF) and RF dams with and without ev6 were exposed at hatch to hatchmates infected with ALV Subgroup A (Strain RPL-40). The RPL-40 viremia, shedding, and virus neutralizing antibodies were measured among pullets from two hatches at 22 wk of age. Although significant (P less than .05) differences between hatches in the immune response to contact infection were noted among ev6+ pullets, significantly fewer ev6+ pullets seroconverted than their ev6- hatchmates. At 22 wk of age, significantly more lymphomas were also found among ev6+ pullets than among ev6- hatchmates. In flocks wherein both parents and progeny were homozygous resistant to Subgroup E virus, there was no deterimental maternal effect on RF progeny from SF dams that carried ev21. These results also confirm that selection for genetic cellular resistance to Subgroup E ALV infection eliminates congenital transmission of EV21.

Influence of maternal antibody on avian leukosis virus infection in White Leghorn chickens harboring endogenous virus-21 (EV21)

Slow-feathering (SF) white leghorn dams harboring the endogenous viral gene ev21, which encodes for complete endogenous virus-21 (EV21), and rapid-feathering (RF) dams lacking EV21 were immunized with a live field strain of avian leukosis virus (ALV) subgroup A. One group of SF dams and one group of RF dams were not immunized and were maintained to produce chicks lacking maternal ALV antibody. When the SF dams were crossed with line 15B1 males, the resulting male progeny were SF, EV21-positive, and the females were RF, lacking EV21 or congenitally infected with EV21. EV21-positive and -negative progeny of immunized and unimmunized SF and RF dams were exposed to ALV at hatching. Viremia, antibody development, cloacal shedding, and tumors in chickens lacking EV21 were compared with those in chickens with EV21. Congenital transmission of EV21 from SF dams to RF female chicks was significantly higher in immunized dams than in unimmunized dams. Maternal ALV antibody delayed infection with ALV and reduced viremia and cloacal shedding of virus in progeny. The effect of maternal antibody on ALV infection was much more pronounced in progeny lacking EV21 than in progeny harboring EV21. The data suggest that the development of ALV infection and tumors may be influenced by status of infection with EV21 and by the immune status of dams.

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.

Ducks: a new experimental host system for studying persistent infection with avian leukaemia retroviruses

Long-term persistence of the avian leukosis virus (ALV), the transformation-defective mutant of Prague strain Rous sarcoma virus subgroup C (td PR-C) was established in heterologous duck hosts after infection in mid-embryogenesis. Transient viraemia was observed for about 4 weeks after hatching and was lost in most of the infected ducks by about 6 months. Loss of viraemia was accompanied by the increasing synthesis of virus-neutralizing antibodies. In spite of strong virus-neutralizing antibodies, virus was detected by the cocultivation assay in duck tissues throughout the observation period up to 5 years. In the viraemic phase of infection, we found integrated proviruses in various tissues, preferentially in stomach muscle tissue and in the thymus. The long-term persistence of virus was frequently accompanied by liver necrosis and neoplastic diseases. Injection of td PR-C virus into early embryos resulted in more pronounced infection accompanied by an increased copy number of viral DNA per cell, high mortality and remarkable atrophy of thymus tissue in infected ducklings.

Immune abnormalities in avian erythroblastosis virus-infected chickens

Infection of animals with retroviruses frequently leads to immunosuppressed states. The immune status of chickens injected with the replication-defective avian erythroblastosis virus (AEV), with its naturally occurring subgroup B helper virus (avian erythroblastosis-associated virus; AEAV), was evaluated daily and compared to the immune status of age-matched uninfected control chickens. Spleen cells from AEV-infected chickens gave depressed responses to concanavalin A, phytohemagglutinin, and pokeweed mitogen beginning 3 days after injection of the virus and continuing until death. Spleen cells from AEV-infected chickens suppressed the T-cell mitogen-induced blastogenic responses of spleen cells from uninfected chickens. The ability of spleen cells from infected chickens to suppress mitogen-induced blastogenic responses of spleen cells from normal chickens in coculture was transient beginning 4 days following viral inoculation, reaching peak levels of suppression on day 7 and disappearing by day 12. Cytolysis of splenic cells from AEV-infected chickens with polyclonal anti-T-cell-serum removed the suppressor activity. Addition of conditioned medium rich in T-cell growth factor resulted in a partial restoration of the blastogenic responsiveness of splenic cells from 6-day post-AEV-infected chickens. Addition of exogenous T-cell growth factor had no effect on the suppressed blastogenic responsiveness of spleen cells from 12-day post-AEV-infected chickens, and it had no effect on coculture suppression. In addition to suppressed T-cell responses to polyclonal mitogen-induced proliferation in vitro and transiently expressed T-suppressor cells, thymic atrophy and structural disruption was observed in AEV-infected chickens.

Interactions between endogenous virus loci ev6 and ev21. 1. Immune response to exogenous avian leukosis virus infection

The effects of ev6, ev21, sex, and hatch, were studied with respect to avian leukosis virus (ALV) viremia, cloacal shedding, and antibody response among RPL-40 virus-infected White Leghorns that carried ev6 and ev21 in all combinations. Among the four possible ev genotypes, chickens that carried only ev21 were the most immunologically tolerant to RPL-40 infection. Incidence of RPL-40 viremia was lowest among hatchmates that lacked both ev genes. Analysis of variance indicated significant interactions between ev6 and ev21 with respect to all responses. Among ev21+ slow-feathering (SF) chickens, the incidence of viremia and shedding of RPL-40 was reduced in the presence of ev6 when compared with ev6- hatchmates. Conversely, among ev21- rapid-feathering (RF) chickens, ev6 significantly enhanced the incidence of RPL-40 viremia when compared with ev6- hatchmates. The endogenous virus, ev6, markedly reduced recovery of the endogenous virus (EV21) from plasmas of slow-feathering chickens. When both flocks were terminated at 21 wk of age, significantly more ev21+ SF females had died from or developed RPL-40-induced tumors than ev21- hatchmates.

Interactions between endogenous virus loci ev6 and ev21. 2. Congenital transmission of EV21 viral product to female progency from slow-feathering dams

The influence of the endogenous virus ev6 on congenital transmission of EV21, the infectious viral product encoded by locus ev21, and the immune response to exogenous avian leukosis virus (ALV) infection was studied in rapid-feathering (RF) female progeny from four classes of slow-feathering (SF) (ev21+ and RF (ev21-) dams with and without ev6. Apart from transmitting infectious EV21 and ev6 to progency, dam ev genotype did not influence the immune response or shedding of RPL-40. The endogenous virus envelope glycoprotein encoded by ev6, however, completely restricted shedding and congenital transmission of infectious endogenous virus EV21, from SF dams. After 19 wk of exposure to ALV strain RPL-40 infected cage mates, only 11% of the congenitally infected female progeny mounted neutralizing antibodies against RPL-40, whereas 73% of their noncongenitally infected sisters seroconverted. More ev6+ female progeny, however, were shedders of RPL-40 and developed tumors than ev6- sisters. Among progeny from the four classes of dams, EV21 congenitally infected hens had the highest incidence (31%) of RPL-40-induced tumors.

Follicular exclusion of retroviruses in the bursa of Fabricius

To gain insight into the regulation of retroviral infection at the cellular level, we analyzed the distribution of retroviral antigen and nucleic acid in the bursa of Fabricius of the parents and progeny of two highly inbred lines of chickens, one resistant and the other susceptible to infection. Line 15I5 chickens and line 7(2), which are C/C and C/A, respectively, and 15I5 x 7(2) F1 chickens were infected with either RAV-1 or RAV-49 avian leukosis virus (ALV). Most bursal follicles of F1 chickens infected with either virus contained a variable mixture of virus-positive and virus-negative cells and a few (1 to 20%) were void of detectable virus. However, in either parental line the respective virus was uniformly expressed among all follicles. The follicles which excluded virus in the F1 birds were indistinguishable from other infected follicles in the same bursa or in uninfected birds on the basis of histology or cellular antigen expression. It was concluded that virus susceptibility is most likely determined at the bursal stem cell level of differentiation, possibly by a process of allelic exclusion at the retroviral receptor locus.

Influence of congenital transmission of endogenous virus-21 on the immune response to avian leukosis virus infection and the incidence of tumors in chickens

After contact exposure to Strain RPL-40 avian leukosis virus-infected hatchmates, a dilatory neutralizing antibody response and prolonged RPL-40 viremia was found among most pullets that were congenitally infected with endogenous virus 21 (EV21). Conversely, most of the hatchmates that were not congenitally infected seroconverted within 10 wk after exposure to Strain RPL-40 virus. Compared with noncongenitally infected hatchmates, EV-21 infection-induced tolerance to pathogenic avian leukosis viruses was reflected in a significantly higher incidence of lymphomas in congenitally infected hens. The rate of seroconversion and the incidence of RPL-40 virus-induced tumors among noncongenitally infected daughters from slow-feathering dams homozygous resistant to EV were similar to those found among daughters of rapid-feathering dams that lacked genetic locus ev21. Results suggest that selection for resistance to EV may eliminate tolerance toward oncogenic field strains of avian leukosis viruses and may improve the performance of progeny from a feather-sex cross.