Search PubMed⌕ Search

Biomedical subjects

R L Witter

Publications and source records attributed to R L Witter.

At least 37 records · Page 2Linked to original sources
PubMed1994

Poultry vaccines of the future.

Current poultry vaccines are based either on live attenuated organisms or on killed organisms. Future vaccines also may be based on deletion mutants, live viral or bacterial vectors that express foreign genes, and naked DNA. Vaccines have different purposes, depending on the disease, which govern their intrinsic characteristics. Improvement of vaccine efficacy can be addressed by modifications of the vaccine and its administration, modifications in the capacity of the host to mount an immune response, and modifications of environmental factors. The concept of "designer vaccines" for matching vaccines that deliver specific antigenic peptides to chickens with the MHC haplotype that best presents those peptides to T cells is discussed.

Animal Husbandry↗
PubMed1993

PCR detection of amplified 132 bp repeats in Marek's disease virus type 1 (MDV-1) DNA can serve as an indicator for critical genomic rearrangement leading to the attenuation of virus virulence.

A radioactive PCR test was developed that amplified the very virulent Marek's disease virus-1 (vvMDV-1) DNA sequence containing the 132 bp repeats. In apathogenic MDV-1 (CVI 988, Rispens), amplified DNA bands containing multiple copies of 132 bp repeats were identified. In the present study this PCR technique was used to monitor the passage level of vvMDV-1 in chicken embryo fibroblasts (CEF) in which the number of tandem 132 bp repeats was increased. It was found that at passage level 32 of vvMDV-1-B isolate, the 132 bp tandem repeat was already markedly amplified and its pattern resembled that of the MDV-1 (CVI 988, Rispens) vaccine virus DNA. In the vvMDV-1Z strain, amplification of the 132 bp repeat was not detectable at a similar passage level. The PCR test demonstrated that the apathogenic MDV-1 Md11/75c virus developed by extensive in vitro passaging has amplified 132 bp DNA repeats similar to those of the commercial vaccine virus (CVI 988, Rispense). It was also found that the pattern of viral RNA from infected cells detectable by Northern blot hybridization was markedly changed from a 2.4 kb RNA species in cells infected with vvMDV-1 viruses, to four RNA species (ranging from 2.2 to 4.4 kb) in cells infected with passage 32 of MDV-1-B strain, to a very large number of undefined RNA species synthesized in cells infected with attenuated MDV-1 viruses (CVI 988, Rispens and Md 11/75c).

Animals↗
PubMed1993

Fowlpox virus recombinants expressing the envelope glycoprotein of an avian reticuloendotheliosis retrovirus induce neutralizing antibodies and reduce viremia in chickens.

Eight stable fowlpox virus (FPV) recombinants which express the envelope glycoprotein of the spleen necrosis virus (SNV) strain of reticuloendotheliosis virus (REV), an avian retrovirus, were constructed. These recombinants differ in the genomic location of the inserted genes, in the orientation of the insert relative to flanking viral sequences, and in the promoter used to drive expression of the env gene. Of these variables, promoter strength seems to be the most crucial. The P7.5 promoter of vaccinia virus, which is commonly used in the construction of both vaccinia virus and FPV recombinants, resulted in lower levels of expression of the envelope antigen in infected chicken cells compared with a strong synthetic promoter, as determined by immunofluorescence and enzyme-linked immunosorbent assay. Two peptides encoded by the env gene, the 21-kDa transmembrane peptide and a 62-kDa precursor, were detected by immunoprecipitation of labeled proteins from cells infected with recombinant FPVs, using monoclonal antibodies against REV. These peptides comigrated with those precipitated from REV-infected cells. One of the recombinants (f29R-SNenv) was used for vaccination of 1-day-old chickens. Vaccinated chicks developed neutralizing antibodies to SNV more rapidly than did unvaccinated controls following SNV challenge and were protected against both viremia and the SNV-induced runting syndrome.

Animals↗
PubMed1992

Reticuloendotheliosis in a wild turkey (Meleagris gallopavo) from coastal Georgia.

An emaciated wild turkey (Meleagris gallopavo) exhibiting neurologic signs was found on Ossabaw Island, Chatham County, Georgia (USA) on 11 April 1989. The neurologic abnormalities observed included ataxia, drooping wings, head tremors, torticollis, and circling. At necropsy, discrete yellowish-white nodules, varying in size from 2 to 5 mm, were present in the spleen. White nodular lesions approximately 2 mm in diameter were observed beneath the mucosal surface of the distal esophagus. Histopathologic examination of the splenic nodules disclosed large numbers of primitive lymphoreticular cells with leptochromatic nuclei and abundant, slightly basophilic cytoplasms. The mitotic index in these cells was moderate to high. Similar neoplastic cells composed the masses observed in the esophagus. Multifocal, mild perivascular cuffing with mononuclear cells was found in the lumbar spinal cord, brain, and brain stem. Reticuloendotheliosis virus, subtype 3, was isolated from samples of the spleen and liver.

Animals↗
PubMed1989

Augmentation of retrovirus-induced lymphoid leukosis by Marek's disease herpesviruses in White Leghorn chickens.

Our objective was to determine whether the cell-associated herpesvirus vaccines used in chickens to control Marek's disease tumors can augment development of lymphoid leukosis (LL) induced by exogenous avian leukosis virus (ALV). Various single or mixed Marek's disease vaccines were inoculated at day 1, and ALV was injected at 1 to 10 days, with chickens of several experimental or commercial strains. Development of LL was monitored at 16 to 48 weeks in various experiments. In several strains of chickens we repeatedly found that the widely used serotype 3 turkey herpesvirus vaccine did not augment LL in comparison with unvaccinated controls. However, LL development and incidence were prominently augmented in several chicken strains vaccinated with serotype 2 vaccines, used alone or as mixtures with other serotypes. In one chicken strain, augmentation was demonstrated after natural exposure to ALV or serotype 2 Marek's disease virus viremic shedder chickens. Augmentation of LL by virulent or attenuated Marek's disease viruses of serotype 1 was intermediate in effect. Serotype 2 Marek's disease virus augmentation of LL was prominent in three laboratory lines and one commercial strain of White Leghorns, but it was not observed in an LL-resistant laboratory line or four commercial strains susceptible to ALV infection. Chickens developed similar levels of viremia and neutralizing antibodies to ALV regardless of the presence of augmentation of LL, suggesting that the mechanism of enhanced LL did not result from differences in susceptibility or immune response to ALV. We postulate that the serotype 2 herpesviruses may augment LL through one of several possible influences on bursal cells that are subsequently transformed by exogenous ALV.

Animals↗
PubMed1989

Histomoniasis and reticuloendotheliosis in a wild turkey (Meleagris gallopavo) in North Carolina.

A moribund wild turkey (Meleagris gallopavo) died shortly after it was discovered in Martin County, North Carolina (USA). The 4.3-kg female turkey appeared in good condition with no visible external lesions or evidence of injury. There were 2- to 5-mm yellow-white plaques on the mucosal surfaces of the oral cavity and mid-esophagus. The liver had large, multifocal, irregular pale areas on cut and uncut surfaces. The spleen contained multifocal, pale, hard, nodules. Microscopic changes in the liver consisted of large multifocal coalescing areas of necrosis. Occasional spherical 10 to 15 microns in diameter organisms consistent with Histomonas meleagridis were present in the necrotic areas. Viable hepatic parenchyma contained multifocal infiltrations of numerous mononuclear cells interpreted as neoplastic cells resembling lymphoblasts and plasma cells. Similar neoplastic cell infiltrates, consistent with the lymphoproliferative disease reticuloendotheliosis, were present in spleen, lung, and esophageal and oral mucosa. Reticuloendotheliosis virus, subtype 2, was isolated from samples of liver and spleen.

Animals↗
PubMed1987

Serologic differences among nondefective reticuloendotheliosis viruses.

Antigenic relationships among 26 isolates of reticuloendotheliosis virus (REV) obtained from several avian species were compared by cross neutralization tests with polyclonal chicken sera and by immunofluorescent assays with monoclonal antibodies to REV strain T. The isolates were all strongly related by neutralization assays and thus probably constitute a single serotype. However, 3 antigenic subtypes were suggested by minor but distinct differences in neutralization titers. The validity of these 3 subtype designations was confirmed by differential reactivity of viral isolates to selected monoclonal antibodies. Subtype-associated differences in serum antibody titers were noted following the inoculation of chickens with the REV isolates.

Animals↗
PubMed1987

C-myc activation in an unusual retrovirus-induced avian T-lymphoma resembling Marek's disease: proviral insertion 5' of exon one enhances the expression of an intron promoter.

Characterization of nonacute retrovirus-induced neoplasms have greatly facilitated our understanding of the mechanisms by which host protooncogenes are activated. Here we report the molecular characterization of a newly identified chicken lymphoma, which does not involve the bursa of Fabricius. This lymphoma, specifically induced by reticuloendotheliosis virus (REV), is similar in tumor location and T-cell origin to Marek's disease, a herpesvirus-induced T-lymphoma. We show the c-myc is the specific target locus for REV insertion. Integrated proviruses are all located upstream of the c-myc coding exons, and 60% are 5' to the first noncoding exon. One-half of the proviruses are oriented in the opposite transcriptional direction as the c-myc gene. This insertion pattern is in contrast to the pattern in B-lymphomas induced by the same virus. While some of the proviruses in these T-lymphomas used the 3' LTR promoter to transcribe the downstream c-myc gene, others apparently activated a common, cryptic promoter located in the first intron. To our knowledge, this is the first molecular description of an avian T-lymphoma induced by a nonacute retrovirus.

Animals↗
PubMed1986

Resistance of line 6(3) chickens to reticuloendotheliosis-virus-induced bursa-associated lymphomas.

Chickens of lines 6(3) and 151(5) X 7(1) were inoculated with the chick syncytial strain of reticuloendotheliosis virus (REV) or with the Rous-associated virus-I of avian leukosis virus (ALV) at hatching. At 4, 10, 16, and 36 weeks post inoculation (PI), chickens were tested for REV- and ALV-induced viremia and antibody. The incidence of REV- or ALV-induced bursa-associated lymphomas in line 6(3) chickens was compared with that in line 151(5) X 7(1) chickens. Inoculation of REV at hatching resulted in immunological tolerance to the virus in line 6(3) but not in line 151(5) X 7(1) chickens. Between 70% and 100% of line 6(3) chickens remained viremic and lacked REV antibody throughout the experimental period of 36 weeks. In contrast, ALV-inoculated chickens of both lines had antibody by 16 weeks PI. The frequencies of REV- and ALV-induced bursa-associated lymphomas in line 6(3) chickens were significantly lower than in line 151(5) X 7(1) chickens. Further, the incidence of bursa-associated lymphomas induced by REV in line 151(5) X 7(1) chickens was significantly lower than that induced by ALV. These results suggest that: (1) the genetic constitution of the host may influence the immunological response to REV infection; (2) chickens resistant to ALV-induced bursa-associated lymphomas are equally resistant to such lymphomas induced by another unrelated avian retrovirus, REV; and (3) ALV is a more potent inducer of bursa-associated lymphomas than REV.

Animal Husbandry↗
PubMed1986

Monoclonal antibodies against avian reticuloendotheliosis virus: identification of strain-specific and strain-common epitopes.

We report the generation and partial characterization of a panel of 11 monoclonal antibodies (MCA) made against the nondefective strain T reticuloendotheliosis virus (REV). In an enzyme-linked immunosorbent assay (ELISA), nine MCA cross-reacted with both homologous strain T and heterologous strain chick syncytial virus (CS), whereas two MCA were strain specific and reacted with strain T but not with CS. Competitive antibody inhibitory ELISA tests demonstrated that the nine MCA recognized at least two distinct type-common epitopes. By using MCA-mediated immunoprecipitation and polyacrylamide gel electrophoresis analysis, we identified a 62,000 dalton glycoprotein that may contain both type-common epitopes and a 21,000 dalton glycoprotein that contains one of these epitopes. The competitive antibody inhibitory ELISA tests confirmed that the remaining two MCA recognize a strain T-specific epitope. We identified a 54,000 to 72,000 dalton glycoprotein that contains the type-specific epitope. All of the MCA reacted in an ELISA assay with cell-free virus preparations, suggesting that the polypeptides we identified are virion envelope glycoproteins. To identify the nonglycosylated precursor proteins, we treated infected cells with tunicamycin. We found a 48,000 polypeptide that was the nonglycosylated precursor to the 54,000 to 72,000 glycoprotein, and 48,000 and 20,000 dalton proteins that were the nonglycosylated precursors to the 62,000 and 21,000 dalton glycoproteins, respectively. These MCA may be of value in the field. They were able to distinguish in preliminary tests in ELISA between strains T and CS, which were otherwise undistinguishable in assays that made use of conventional polyvalent serum.

Animals↗
PubMed1986

Tests of association of immunoglobulin allotype genes and viral oncogenesis in chickens.

Chickens from Regional Poultry Research Laboratory (RPRL) inbred line 6(3) are resistant to virally-induced Marek's disease (MD) and lymphoid leukosis (LL) and are relatively strong regressors of virally-induced Rous sarcomas. In contrast, RPRL line 100 chickens are highly susceptible to MD and LL and are weaker regressors of Rous sarcomas than line 6(3). RPRL lines 100 and 6(3) differ for alleles at the IgG-1 (G-1) allotype locus, but have identical IgM-1 (M-1) allotype alleles. To test the possible association of the G-1 locus with variations in resistance to virally-induced tumors, homozygous and heterozygous genotypes among F3 crosses were infected. F3 chickens with different G-1 types were comparable in their resistance to MD tumors following inoculation with the JM strain of the MD virus, and for their ability to regress Rous sarcoma tumors induced by the Rous sarcoma virus (RSV) RAV-1. However, following RAV-1 virus infection a smaller proportion of G-1a/G-1aF3 or F4 birds developed LL tumors than G-1a/G-1e and G-1e/G-1e birds. Genes determining immunoglobulin heavy chains were therefore associated with a recessive resistance to B-cell lymphomagenesis in chickens.

Animals↗
PubMed1986

Gene insertion into the chicken germ line by retroviruses.

We injected chick syncytial strain of reticuloendotheliosis virus (CS-REV) and wild type and recombinant avian leukosis virus (ALV) near the blastoderm of unincubated fertilized embryos and CS-REV intra-abdominally at day of hatch, and we progeny tested the surviving ALV viremic males and REV viremic males and females for transmitted viral genetic material. A number of positive progeny were identified and their deoxyribonucleic acid (DNA) analyzed for restriction enzyme fragments that hybridized with viral genetic material. Most of the progeny had simple restriction enzyme patterns unlike the viremic parents or congenitally infected progeny. This is suggestive evidence that retroviral genetic information has been inserted into the germ line of chickens.

Animals↗
PubMed1985

The structure of Marek disease virus DNA: the presence of unique expansion in nonpathogenic viral DNA.

DNA of Marek disease virus (MDV) consists of two unique regions UL and US flanked by long inverted repeat regions TRL and IRL, and short inverted repeat regions TRS and IRS, respectively, similar to herpes simplex virus DNA. Comparison of restriction patterns between pathogenic and nonpathogenic MDV DNA was made to identify a region of viral DNA different between these two types of MDV, as it may be responsible for the tumorigenicity of MDV in chickens. The results indicated that BamHI-D and -H, located at the long inverted repeat regions TRL and IRL, were specifically expanded in nonpathogenic viral DNA. The location of the expanded region has been determined within 1.5 kilobase pairs of the Bgl I/Pst I fragment of BamHI-D and -H, close to the junction between the inverted repeat and the unique region. The possibility that a gene responsible for tumor induction may be disrupted by such expansion has been discussed.

Animals↗
PubMed1985

Genomic expansion of Marek's disease virus DNA is associated with serial in vitro passage.

An EcoRI restriction endonuclease pattern of Md11 virus DNA, a very virulent strain of Marek's disease virus (MDV), was obtained by using total cellular DNA from infected cells. With the EcoRI restriction endonuclease pattern and a published BamHI map of MDV (Fukuchi et al., J. Virol. 51:102-109), we constructed a partial EcoRI map of a series of MDV clones (gift from H. J. Kung). The clones were used to identify a region of the Md11 genome which is altered as the oncogenic virus is passaged in vitro. This region was mapped into a 1.8-kilobase segment in the inverted-repeat sequences flanking the long unique region of the virus genome. The alteration appeared to result from multiple DNA insertions that produced an increase of 0.6 to 5.4 kilobases. Although the expansion of this region did not diminish the ability of MDV to replicate in vitro, it may be associated with the loss of Marek's disease oncogenicity.

Animals↗
PubMed1985

Insertional activation of c-myc by reticuloendotheliosis virus in chicken B lymphoma: nonrandom distribution and orientation of the proviruses.

Chicken syncytial virus, a member of the reticuloendotheliosis virus family, can induce chicken B lymphomas indistinguishable from those caused by avian leukosis virus. Previously, we have demonstrated that the chicken syncytial virus proviruses in these tumors are linked to the proto-oncogene c-myc. We have now determined the arrangement of chicken syncytial virus proviruses in 22 tumors. The results indicate that these proviruses, without exception, are integrated upstream from the second c-myc exon. At least 70% of these insertion sites are clustered in a 0.5-kilobase region immediately preceding the exon. The proviruses are all arranged in the same transcriptional orientation as c-myc. This type of provirus organization bears strong resemblance to that of the avian leukosis virus proviruses involved in c-myc activation.

Animals↗
PubMed1985

Field trials to test the efficacy of polyvalent Marek's disease vaccines in layer and broiler breeder chickens.

As a follow-up to earlier trials to evaluate the efficacy of polyvalent Marek's disease (MD) vaccines in broilers, four trials were conducted with layer or broiler breeder flocks. Chickens caccinated with trivalent (Md11/75C plus SB-1 plus HVT) and bivalent (SB-1 plus HVT) vaccines were compared with those vaccinated with turkey herpesvirus (HVT) alone. Data from three of the four trials indicated polyvalent vaccines were more efficacious than HVT. However, critical interpretations were confounded by low MD lesion frequencies, unequal exposure in different houses on a farm, and difficulty in the differential diagnosis of mortality due to neoplasms. The data confirmed our earlier observation that trivalent and bivalent vaccines were equally effective. Broiler progeny of breeders vaccinated or contact-infected with Serotype 2 MD virus were well protected by either bivalent or HVT vaccines against challenge with very virulent MD virus strains in the laboratory. A high incidence of lymphoid leukosis was observed in two trials and may have been due to post-hatch exposure to an unidentified environmental source of avian leukosis virus.

Animals↗
PubMed1983

B5 and B15 associated with progressive Marek's disease, Rous sarcoma, and avian leukosis virus-induced tumors in inbred 15I4 chickens.

RPRL 15I4 inbred chickens are nearly histocompatible except for the B5 and B15 haplotypes that determine the major transplantation antigens. B5B5 and B15B15 15I4 chickens were equally and highly susceptible to tumors induced by Marek's disease, Rous sarcoma, or avian leukosis viruses (ALV), suggesting both of these haplotypes may determine a general influence leading to tumor development. The 15I4 birds were highly susceptible to erythroblastosis, and most developed immunological tolerance to the virus after ALV infection.

Animals↗