The influence of the ev 3 locus on the inducibility of serum antibody reactivity for envelope glycoprotein group-specific determinants

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.

Fv-4 resistance gene: a truncated endogenous murine leukemia virus with ecotropic interference properties

Fv-4 is a mouse gene which controls susceptibility to infection by ecotropic murine leukemia virus (MuLV). We previously cloned part of an endogenous MuLV associated with the resistance allele of the Fv-4 gene (Fv-4r). In this report, we describe an extended clone of the Fv-4r allele consisting of a 17-kilobase DNA fragment containing the retroviral sequence and its 5'-flanking sequence. The new DNA clone contains a truncated MuLV with delta pol-env-long terminal repeat sequences but no other MuLV-reactive sequence within 13 kilobases upstream of the truncated MuLV. Transfection of this clone into mouse cells led to transcription of Fv-4 env mRNA, expression of the Fv-4r-specific MuLV envelope protein, and resistance to infection with ecotropic MuLV but not amphotropic and dualtropic MuLVs. Restriction of ecotropic viruses appears to occur at or before viral cDNA synthesis. This result is consistent with a model of receptor interference for Fv-4 restriction. Our data also suggest that the 5' non-MuLV sequence is important for biological function, since a DNA clone which lacks most of the 5'-flanking sequence did not efficiently confer the resistance phenotype.

Responses of chickens lacking or expressing endogenous avian leukosis virus genes to infection with exogenous virus

Line 0 chickens that lack endogenous viral (ev) genes and 15I5 X 7 chickens that carry and express ev genes were inoculated with the avian leukosis virus, RAV-1, at 1 day of age or as embryos, and maintained to 70 days of age. Comparable uninoculated controls were also kept. Most of the day-old inoculated chickens developed antibody by 70 days, but as expected, most of the embryo inoculated chickens remained viremic. Major differences in response between the lines were only noted after day-old inoculation. About 40% of Line 0 died of a specific nonneoplastic syndrome (NNS) while none of the 15I5 X 7 chickens did. Line 0 also developed neutralizing antibodies at a much earlier age than 15I5 X 7 and, consequently, virus was cleared from the serum much earlier. Day-old RAV-1 infection of Line 0 also lowered hematocrit more at 14 and 21 days of age than in 15I5 X 7 chickens. Body weight was clearly reduced at all ages in both lines of chickens by both day-old and embryo inoculation. After embryo inoculation, hematocrit was lowered in both lines of chickens between 28 and 42 days of age. Immune response to sheep red blood cells and Brucella abortus was only slightly and inconsistently reduced by inoculation of RAV-1 by both routes in both lines of chickens. It was concluded that the major influences of ev gene expression was to reduce the incidence of NNS and the neutralizing antibody response after RAV-1 inoculation of day-old chicks.

Avian leukosis virus infection: analysis of viremia and DNA integration in susceptible and resistant chicken lines

Avian leukosis viruses induce lymphoid leukosis, a lymphoma which develops within the bursa of Fabricius several months after virus infection. Chickens from the Hyline SC and FP lines are, respectively, susceptible and resistant to avian leukosis virus-induced lymphoid leukosis. We examined plasma and cellular DNA obtained from avian leukosis virus-infected chickens for the presence of viremia and integrated viral sequences to determine whether the extent of virus infection is comparable in individuals of both lines. A less than twofold difference in the frequency of viremia was detected between chickens of the two different lines. Although the analysis of plasma samples, which were obtained at different times postinfection, demonstrated that the duration of viremia was comparable in both susceptible and resistant chickens, the onset of the viremia observed in susceptible chickens generally preceded by 1 week that observed in resistant chickens. Moreover, integrated viral sequences were detected in approximately 90% of the SC and 40% of the FP chickens. The appearance of infectious virus in the plasma was, in general, associated with the presence of integrated viral sequences in both the bursal cells and the erythrocytes obtained from the same chicken. The presence of both the viremia and the integrated viral DNA sequences was transient, suggesting a mechanism for the elimination of virus-infected cells in both susceptible and resistant chickens. Furthermore, at 5 weeks postinfection no integrated exogenous viral sequences were detected in splenic lymphocytes obtained from either chicken line, regardless of whether these chickens were viremic or had integrated viral sequences detectable in other tissues. Our results indicate that extensive avian leukosis virus replication occurs in approximately 50% of the FP and 100% of the SC chickens. Although it appears that the viral infection spreads more quickly in the SC chickens, our results afford no obvious explanation of the resistance to the development of lymphoma exhibited by FP chickens.