Interferon Production and Host Resistance to Type II Avian (Marek''s) Leukosis Virus (JM Strain)

Interferon production in both susceptible S- and resistant K-line chickens infected with type II leukosis virus of JM strain and turkey herpesvirus was studied. The resistant line of chickens produced higher levels of interferon than did the susceptible with JM virus infection during the experimental period. When both susceptible S-and resistant K-line chicks were vaccinated with turkey herpesvirus, the interferon production was quantitatively similar in the two lines.     

Complement Fixation Reaction for the Diagnosis of Type II Avian (Marek's) Leukosis

The present study was designed to find a complement fixation (CF) reaction for the diagnosis of type II lymphoid leukosis, to learn some of the characteristics of the CF antigen, and to investigate the development of CF antibody response to this infection. JM virus-specific antigen was demonstrated in tumorous chicken tissue, in JM virus-infected chick embryo material, in JM virus-infected chicken kidney, and in duck embryo fibroblast tissue culture by using JM virus-immune rabbit serum. This CF antigen did not show cross-reactivity with Rous sarcoma virus or with RIF-type viruses. It was partially heat-labile. The CF activity was restored at —70 C for 10 months and was resistant to intermittent freeze-thaw treatment. The CF antigen may be denatured by ethyl alcohol, but no significant deleterious effects were noted after ether or chloroform treatment. JM virus-specific CF antibody could not be demonstrated by the direct complement dilution method or by the indirect or inhibition form of the CF test in infected or immunized chicken sera.     

In Vitro Chick Embryo Cell Response to Strain MC29 Avian Leukosis Virus

Strain MC29 avian leukosis (myelocytomatosis) virus induced infection, elaboration of virus, and morphological alteration in chick embryo cells in vitro. Virus liberation began within 18 hr, morphological change was detectable at about 40 hr, and the cultures could be completely altered within 80 hr after infection. Altered cells were about half the volume and grew at approximately twice the rate of uninfected elements. The output of virus estimated by electron microscopy was about 140 particles per cell per hr. Deoxyribonucleic acid remained constant, but ribonucleic acid increased in both infected and control cells in adjustment to culture environment. The rates of uptake and incorporation of ³H-uridine and the incorporation of ³H-thymidine increased in the infected cells with onset of morphological change but were unaffected by processes of infection and virus elaboration per se. Incorporation of a ¹⁴C-amino acid mixture was slightly greater in the infected than in control cells. The speed of continuity of infection and massive morphological alteration constitute a unique response to avian tumor viruses, and the system gives promise of singular value for detailed studies of the processes of infection and morphological change.     

Component of Strain MC29 Avian Leukosis Virus with the Property of Defectiveness

Three clones of morphologically altered cells (L(-)MC29) of singular properties were isolated from MC29 (subgroup A) leukosis virus-infected chick embryo cells. Supernatant fluids from cultures of the cloned cells produced no transforming or interfering activity on chick embryo cells susceptible to known avian leukosis-sarcoma viruses. No virus associated with the cells was demonstrable by fluorescent-antibody staining or by electron microscopy. All L(-)MC29 clone cells were activated, however, by four strains of Rous-associated viruses (RAV) representative of A, B, C, and D subgroup avian leukosis viruses and by two strains of MC29 virus. Virus L(-)MC29 cells activated by superinfection with RAV-1 and RAV-2 was characterized by helper-dependent and helper-independent properties. These findings suggest that the strain MC29 leukosis virus, or a component thereof, possesses properties of defectiveness similar to those of the Bryan high-titer Rous sarcoma virus.     

Interferon and Host Resistance to Rauscher Virus-induced Leukemia

A random bred strain of mice (CD-1) was shown to develop resistance to Rauscher leukemia virus (RLV) as the animals matured. Resistant adult mice developed relatively high-serum levels of interferon (150 to 2,000 units per ml) in contrast to susceptible 21-day-old animals in which interferon levels were undetectable or low (less than 20 to 200 units per ml). A similar correlation between resistance and interferon levels was observed in comparisons between resistant CD-1 and susceptible BALB/c mice. The F(1) hybrids of CD-1 x BALB/c and BALB/c x CD-1 matings manifested an intermediate degree of susceptibility and interferon production. The difference in interferon production by CD-1 and BALB/c mice was specific for the RLV-host interaction, since both strains produced equal serum levels of interferon in response to Sindbis and Newcastle disease viruses. The mortality of CD-1 suckling mice infected with Rauscher leukemia virus was decreased by treatment with interferon. These data demonstrate an association between interferon production by the host and the observed relative resistance of the CD-1 strain of adult mice to the subsequent malignant transformation. This virus-host relationship provides an excellent model for further study of factors affecting the development of virus-induced leukemia.     

Comparison of Indirect Hemagglutination and Immunodiffusion Tests for Detecting Type II Leukosis (Marek's) Infection in S- and K-Line Chickens

The indirect hemagglutination and immunodiffusion tests were compared for detection of antigen and antibody to JM strain of leukosis virus infection between S- and K-line chickens. The indirect hemagglutination test was more sensitive than the immunodiffusion test for detecting the smallest amount of viral antigen and corresponding antibody in the plasma of infected chickens. The Cornell S-line had higher levels of antigen and antibody as compared with the Cornell K-line during the 20-week experimental period.     

Parasite Tolerance and Host Competence in Avian Host Defense to West Nile Virus

Competence, or the propensity of a host to transmit parasites, is partly underlain by host strategies to cope with infection (e.g., resistance and tolerance). Resistance represents the ability of hosts to prevent or clear infections, whereas tolerance captures the ability of individuals to cope with a given parasite burden. Here, we investigated (1) whether one easy-to-measure form of tolerance described well the dynamic relationships between host health and parasite burden, and (2) whether individual resistance and tolerance to West Nile virus (WNV) were predictable from single cytokine measures. We exposed house sparrows (HOSP) to WNV and measured subsequent changes in host performance, viral burden, and cytokine expression. We then used two novel approaches (one complex, one simpler) to estimate tolerance within-individual HOSP using four separate host performance traits. We lastly investigated changes in the expression of pro-inflammatory cytokine interferon-γ (IFN-γ) and anti-inflammatory cytokine interleukin-10 (IL-10). Both approaches to estimating tolerance were equivalent among WNV-infected HOSP; thus, an easy-to-measure tolerance estimation may be successfully applied in field studies. Constitutive expression of IFN-γ and IL-10 were predictive of resistance and tolerance to WNV, implicating these cytokines as viable biomarkers of host competence to WNV.     

Morphogenesis of Avian Infectious Bronchitis Virus and a Related Human Virus (Strain 229E)

Avian infectious bronchitis virus (IBV) and strain 229E, a virus recently recovered from patients with colds, have been shown to possess a similar distinctive morphology in negatively stained preparations. An electron microscopic study of the morphogenesis of IBV in the chorioallantoic membrane and of strain 229E in WI-38 cells was performed. In infected cells, round electron-dense particles 82 mmu in diameter were observed to form by a process of budding from membranes of the endoplasmic reticulum and cytoplasmic vesicles. The particles in IBV-infected cells were similar in size and shape to those in strain 229E-infected cells but showed certain differences in internal structure. The evidence that the particles represent virions and the implications of these findings in the classification of this virus group are discussed.     

Yellow Fever Vaccine. II. Antigenicity and Neurovirulence of a Vaccine Seed Free from Avian Leukosis Virus

Avian leukosis virus (ALV)-free candidate primary and secondary seed lots were indistinguishable from corresponding ALV-contaminated lots with respect to (i) potency as measured by titration in newborn and weanling mice and in the MA-104 plaque system, (ii) degree of viscerotropism as measured by viremia in monkeys, (iii) neurotropism as determined by the monkey neurovirulence test, and (iv) potency as determined by antibody response in monkeys inoculated by the intracerebral route.     

禽白血病病毒J亚群env基因的克隆和序列分析

应用多聚酶链反应（PCR）的方法扩增出ADOL-4817毒株的囊膜蛋白env基因,并克隆进大肠杆菌。经核酸序列分析证明,env基因的大小为1746 bp,其中gp85和gp37由1554 bp组成,可翻译成517个氨基酸,分子量为57.7 D。根据糖基化位点N-X-S/T的特点,发现ADOL-4817的env蛋白有15个潜在的糖基化位点。同源性分析证明,ADOL-4817的env基因与其它ALV-J的env基因序列同源性为88.8%～92.4%,而与外源性ALVs的相应序列的同源性仅为40.5%～51.4%,然而,与内源性的EAV-HP毒株的类env基因的同源性高达91.2%;另外,ADOL-4817毒株的gp37在C末端多了13个氨基酸。这些结果提示,ALV-J的env基因存在广泛的变异性,env基因可能来源于内源性和外源性ALVs的重组。     

Interactions between Marek's Disease Herpesvirus and Avian Leucosis Virus in Tissue Culture

A GROUP B herpesvirus is important in the aetiology of Marek's disease, a highly contagious lymphoproliferative disease of chickens^1,2. Chicks inoculated with enveloped Marek's disease herpesvirus (MDHV), extracted from feather follicle epithelium of chickens with the disease, developed tumour-like aggregates of lymphoid cells in the viscera and frequently in the peripheral nerves^3,4. Cultures of chicken embryo fibroblast (CEF) cells infected with MDHV develop discrete foci of altered cells⁵. Our data show that MDHV infection of cultures of CEF cells, previously infected with an avian leucosis virus (RAV-2), results in both a reduction in the number of MDHV foci and an increase in the complement fixing avian leucosis antigen (COFAL)⁶ titre.     

Genetic Mapping of the Cloned Subgroup A Avian Sarcoma and Leukosis Virus Receptor Gene to the TVA Locus

A chicken gene conferring susceptibility to subgroup A avian sarcoma and leukosis viruses (ASLV-A) was recently identified by a gene transfer strategy. Classical genetic approaches had previously identified a locus, TVA, that controls susceptibility to ASLV-A. Using restriction fragment length polymorphism (RFLP) mapping in inbred susceptible (TVA*S) and resistant (TVA*R) chicken lines, we demonstrate that in 93 F₂ progeny an RFLP for the cloned receptor gene segregates with TVA. From these analyses we calculate that the cloned receptor gene lies within 5 centimorgans of TVA, making it highly probable that the cloned gene is the previously identified locus TVA. The polymorphism that distinguishes the two alleles of TVA in these inbred lines affects the encoded amino acid sequence of the region of Tva that encompasses the viral binding domain. However, analysis of the genomic sequence encoding this region of Tva in randomly bred chickens suggests that the altered virus binding domain is not the basis for genetic resistance in the chicken lines analyzed.Avian sarcoma and leukosis viruses (ASLV) may be classified into several subgroups based on properties of the viral envelope proteins. Five major subgroups of ASLV (A to E) have been defined based on immunological reactivity of the viral envelope proteins, host range, and infection interference patterns (reviewed in reference 18). The subgroup specificity of the virus maps to the env gene, and distinct hypervariable regions within env have been shown to determine the viral subgroup (2, 3, 7, 8).Patterns of susceptibility of inbred chicken lines to infection with the various ASLV subgroups suggest that three loci control viral entry for the five major ASLV subgroups (11, 12, 15, 17). Dominant alleles at the TVA and TVC (TVA*S and TVC*S) loci confer susceptibility to subgroups A and C viruses, respectively. The TVB locus is more complex, with various alleles determining infection by subgroup B, D, and E viruses. TVA, TVB, and TVC appear to act at the level of viral entry into the cell; therefore, it has been assumed that the TV loci encode or control expression of the cellular receptors for ASLV (5, 13).Recently, a gene that confers susceptibility to subgroup A ASLV (ASLV-A) was cloned by a gene transfer strategy (1, 19). Molecular clones containing coding sequences for this gene relieve the block to viral entry when expressed in a number of mammalian cell lines (1, 19). The gene encodes a surface glycoprotein that has been shown to bind directly and specifically to the ASLV-A envelope protein (4, 9). In addition, binding of the receptor protein to ASLV-A envelope protein induces conformational changes in the viral glycoproteins that appear to be associated with viral entry (10). Finally, an antibody to the receptor protein specifically blocks infection of chicken cells by subgroup A viruses, suggesting that this gene encodes the normal ASLV-A receptor on chicken cells (1). Taken together, these results demonstrate that the cloned gene encodes a subgroup A virus receptor.Since it is clear that the cloned gene encodes an ASLV-A receptor, the protein supposed to be encoded by the classical TVA locus, we asked whether the identified receptor gene mapped to the TVA locus. In this paper we show that a restriction fragment length polymorphism (RFLP) of DNA from inbred chickens can be used to demonstrate that the cloned ASLV-A receptor gene maps to within 5 centimorgans (cM) of the TVA locus as defined by susceptibility to ASLV-A, making it highly probable that the cloned gene is TVA. In addition, analysis of the genomic sequences encoding the viral interaction domain of the receptor in both inbred and randomly bred chickens demonstrates that alterations in this region of the receptor are not responsible for the resistance phenotype.

TVA segregation analysis.

Inbred chicken lines homozygous for TVA alleles encoding either sensitivity (TVA*S) or resistance (TVA*R) were used to generate birds in which the TVA segregation pattern could be studied. Regional Poultry Research Lab lines 6₃ (TVA*S/*S TVB*S/*S) and 7₂ (TVA*R/*R TVB*R/*R) (6) were crossed, and the resulting heterozygous F₁ progeny were mated to generate 93 F₂ chicks. The susceptibility phenotype of the F₂ chicks was determined on the basis of tumor formation following subcutaneous injection of 500 focus-forming units (FFU) of subgroup A Bryan high-titer Rous sarcoma virus (RSV) (RAV-1) and 500 FFU of subgroup B Bryan high-titer RSV (RAV-2) into the right and left wing webs, respectively, of 4-week-old chicks. At 2, 3, and 4 weeks postinjection the wings were palpated to check for tumor development. Chicks were scored as positive for susceptibility (e.g., TVA*S/*S or TVA*S/*R) if a tumor of any size formed in the appropriate wing web.Table ​Table11 summarizes the distribution of susceptibility to subgroups A and B RSV in the F₂ chicks. Segregation of TVB yielded roughly the predicted frequency of susceptible (67 observed versus 70 expected) and resistant (26 observed versus 23 expected) progeny for a dominant locus (P > 0.05). In contrast, the distribution of subgroup A-susceptible and -resistant birds deviated significantly from the expected 3:1 ratio, with an excessive number of subgroup A-resistant chicks observed and a ratio of 2:1 (χ² = 3.4) (Table ​(Table1).1). Previous analysis of the segregation of TVA using the same chicken lines did not reveal an altered distribution of sensitive and resistant birds (6), suggesting that the bias seen here may be a chance deviation from the expected ratio. Segregation of two endogenous virus loci, ALVE2 (previously designated ev2) (carried by line 7₂) and ALVE3 (previously designated ev3) (carried by line 6₃), also gave roughly the expected 3:1 ratio in these F₂ chicks (data not shown). When the segregation bias in the ASLV-A-susceptible birds was accounted for, then susceptibility to subgroup A and B RSV segregated independently, as was expected since the TVA and TVB genes have been reported to be unlinked (6). Recent mapping studies also confirmed that TVA and TVB are found on different linkage groups (3a).

TABLE 1

Segregation of resistance and susceptibility to subgroup A and B viruses in F₂ progeny obtained by crossing lines 6₃ and 7₂

Isolation and Identification of a Subgroup A Avian Leukosis Virus from Imported Meat-type Grand-parent Chickens

An exogenous avian leukosis virus (ALV) strain SDAU09C1 was isolated in DF-1 cells from one of 240 imported 1-day-old white meat-type grand parent breeder chicks. Inoculation of SDAU09C1 in ALV-free chickens induced antibody reactions specific to subgroup A or B. But gp85 amino acid sequence comparisons indicated that SDAU09C1 fell into subgroup A; it had homology of 88.8%-90.3% to 6 reference strains of subgroup A, much higher compared to other subgroups including subgroup B. This is the first report for A...     

Evolutionary Repercussions of Avian Culling on Host Resistance and Influenza Virulence

Background

Keeping pandemic influenza at bay is a global health priority. Of particular concern is the continued spread of the influenza subtype H5N1 in avian populations and the increasing frequency of transmission to humans. To decrease this threat, mass culling is the principal strategy for eradicating influenza in avian populations. Although culling has a crucial short-term epidemiological benefit, evolutionary repercussions on reservoir hosts and on the viral population have not been considered.

Methods and Findings

To explore the epidemiological and evolutionary repercussions of mass avian culling, we combine population genetics and epidemiological influenza dynamics in a mathematical model parameterized by clinical, epidemiological, and poultry data. We model the virulence level of influenza and the selection on a dominant allele that confers resistance against influenza [1], [2] in a poultry population. Our findings indicate that culling impedes the evolution of avian host resistance against influenza. On the pathogen side of the coevolutionary race between pathogen and host, culling selects for heightened virulence and transmissibility of influenza.

Conclusions

Mass culling achieves a short-term benefit at the expense of long-term detriments: a more genetically susceptible host population, ultimately greater mortality, and elevated influenza virulence.     

Detection and Molecular Characterization of J Subgroup Avian Leukosis Virus in Wild Ducks in China

To assess the status of avian leukosis virus subgroup J (ALV-J) in wild ducks in China, we examined samples from 528 wild ducks, representing 17 species, which were collected in China over the past 3 years. Virus isolation and PCR showed that 7 ALV-J strains were isolated from wild ducks. The env genes and the 3′UTRs from these isolates were cloned and sequenced. The env genes of all 7 wild duck isolates were significantly different from those in the prototype strain HPRS-103, American strains, broiler ALV-J isolates and Chinese local chicken isolates, but showed close homology with those found in some layer chicken ALV-J isolates and belonged to the same group. The 3′UTRs of 7 ALV-J wild ducks isolates showed close homology with the prototype strain HPRS-103 and no obvious deletion was found in the 3′UTR except for a 1 bp deletion in the E element that introduced a binding site for c-Ets-1. Our study demonstrated the presence of ALV-J in wild ducks and investigated the molecular characterization of ALV-J in wild ducks isolates.