PubMed Health⌕ Search

Biomedical subjects

G T Pharr

Publications and source records attributed to G T Pharr.

17 recordsLinked to original sources
PubMed1999

Natural selection of the Pol gene of bovine immunodeficiency virus.

Genetic variability is a salient feature of lentiviruses, contributing to the pathogenesis of these viruses by enabling them to persist in the host and to resist anti-retroviral treatment. Bovine immunodeficiency virus (BIV), a lentivirus of unknown pathology, infects cattle in the United States and worldwide. Genetic diversity of BIV that is associated with naturally infected cattle is not well studied. We examined the genetic diversity and natural selection of a segment of the BIV pol gene amplified from the leukocyte DNA of naturally infected cattle. A portion of the reverse transcriptase domain (183 bp) of the pol region was targeted for amplification by PCR. PCR products were sequenced directly and aligned. When compared to the sequences of BIV R29-127, a molecular clone of the original BIV R29 isolate, all isolates were greater than 91% identical in nucleotide sequences and 77% identical in amino acid sequences. Pol genotypes were polymorphic at 14% of the nucleotide sites. The ratio of nonsynonymous to synonymous nucleotide substitutions (relative to the number of respective sites, Ka/Ks) was 0.16, indicating that this region of the BIV genome, like that of HIV-1, is subject to purifying selection. Based on the McDonald-Kreitman analysis, this region also was under positive Darwinian selection as HIV-1 and BIV diverged from a common progenitor. Phylogenetic analysis revealed that genotypes were geographically distinct, possibly indicating a common source of infection for animals within a herd.

Amino Acid Sequence↗
PubMed1998

Class II MHC cDNAs in 15I5 B-congenic chickens.

cDNA was obtained from the bursae of Fabricius of chickens from six B-congenic lines developed at this laboratory and studied for expression of class II B-LB genes. Following cDNA amplification, cloning and sequencing, genes were assigned to B-LB loci based on characteristic DNA sequences, amino acid relatedness to characterized genes, and level of expression. Genes from the B-LBI, B-LBII, and B-LBVI loci were differentially expressed in chickens with the B2, B5, B13, B15, or B21 haplotypes. Chickens of all haplotypes expressed a B-LBII gene. Additional B-LB genes expressed included: B-LBI genes in the B5 and B19 haplotypes; a B-LBI/VI recombinant gene in the B2 haplotype; and a B-LBVI gene in the B13 haplotype. The B-congenic lines have demonstrable differences in resistance to Marek's disease (MD), and in responses to MD viral vaccines. This variability in disease resistance may be correlated with polymorphisms in the expressed B-LB genes, or with differential expression of genes at different loci.

Animals↗
PubMed1997

Non-association between Rfp-Y major histocompatibility complex-like genes and susceptibility to Marek's disease virus-induced tumours in 6(3) x 7(2) F2 intercross chickens.

Marek's disease (MD) is a lymphoproliferative disease caused by a member of the herpesvirus family, and the best understood genetic resistance to MD involves the chicken major histocompatibility complex (MHC) B-complex. Preliminary observations have suggested that MHC-like Rfp-Y genes might also influence the incidence of MD. This study describes the differentiation and definition of unique Rfp-Y genes in inbred lines 6(3) and 7(2), lines that possess identical B-complex genes, but that are resistant or susceptible to MD, respectively. To assess if Rfp-Y genes affect susceptibility to MD, 265 6(3) x 7(2) F2 chickens were challenged with the JM strain of MD virus at 1 week of age and were evaluated for MD lesions at up to 10 weeks of age. Genotyping of the F2 chickens for Rfp-Y haplotypes was performed by restriction fragment length polymorphism analysis of genomic DNA using TaqI and a B-FIV probe. Analysis of variance and interval mapping procedures were used to determine association between the Rfp-Y haplotypes and the phenotypic MD values of the F2 chickens. The cosegregation analysis of 265 F2 chickens indicated that there was no association between Rfp-Y haplotypes and MD susceptibility. Furthermore, the fact that the Rfp-Y haplotypes fit the 1:2:1 segregation ratio and the Rfp-Y allele frequencies did not differ significantly from 0.5 in the full population or in selected subpopulations (of either 40 MD-resistant or 39 MD-susceptible chickens) also indicated that Rfp-Y haplotypes do not significantly influence MD susceptibility. We conclude that Rfp-Y haplotypes do not play a major role in determining the genetic susceptibility to MD in 6(3) x 7(2) F2 White Leghorn chickens.

Animals↗
PubMed1997

Avian B cell development.

Development of B cells in chickens proceeds via a series of discrete developmental stages that includes the maturation of committed B cell progenitors in the specialized microenvironment of the bursa of Fabricius. The bursa has been shown to be required for the amplification of the B cell pool and selects for cells with productive immunoglobulin rearrangement events. Other events regulating chicken B cell development such as lymphocyte trafficking and apoptosis are just beginning to be elucidated. Within the bursa, the variable regions of immunoglobulin genes of B cell progenitors are diversified by a process of intrachromosomal gene conversion, where blocks of sequence information are transferred from pseudo-V regions to the recombined variable regions of the immunoglobulin genes. Recently gene conversion has been determined to play a role in the diversification of the immune repertoire in other species. In this review we focus on the current understanding and recent advances of B cell development in the chicken.

Animals↗
PubMed1996

Histocompatibility antigen(s) linked to Rfp-Y (Mhc-like) genes in the chicken.

Major histocompatibility complex (Mhc) genes influencing transplantation rejections were first described in mice within the H2 complex and secondly in chickens within the B complex. In chickens, Rfp-Y haplotypes have recently been identified which contain class I and class II Mhc-like genes that assort independently of the B complex. Three Rfp-Y haplotypes have been defined in a closed breeding flock of line N chickens. In this study, progeny were obtained from line N Rfp-Y heterozygous matings to establish the role of Rfp-Y in transplantation immunity. Rfp-Y incompatibility did not induce significant one-way mixed lymphocyte responses. However, Rfp-Y-incompatible skin grafts were rejected more frequently and at a faster rate than Rfp-Y-compatible grafts by two-week-old chicks. The control Mhc B-incompatible grafts were rejected faster than the Rfp-Y-incompatible grafts; the latter were rejected at speeds that resemble rejection of minor histocompatibility antigens. We conclude that Rfp-Y class I and II Mhc-like genes are linked to the expression of minor histocompatibility antigens in chickens.

Animals↗
PubMed1994

Chicken interferon-mediated induction of major histocompatibility complex class II antigens on peripheral blood monocytes.

Conditioned medium containing immune interferon (IFN) activity was prepared by stimulating spleen lymphocytes obtained from inbred SC chickens with 10 micrograms concanavalin A (Con A) for 48 h. Pretreatment of spleen cells with monoclonal antibody against CD4, but not CD8, abrogated IFN production suggesting that CD4+ lymphocytes are responsible for immune IFN production. Immune IFN was purified 25-fold from Con A conditioned medium using controlled-pore glass column chromatography resulting in an increase in specific antiviral activity from 7 to 3290 units mg-1. Partially purified immune IFN retained antiviral and macrophage-activating factor (MAF)-like activities. Normal peripheral blood macrophages, when cultured in the presence of partially purified immune IFN, showed a dose-dependent increase in cell surface major histocompatibility complex Class II antigen expression by flow cytometry. Northern blot analysis of mRNA obtained from IFN-treated macrophages showed a concomitant increase in Class II gene expression. This effect was more obvious in cells induced for 48 h than in those induced for 24 h. These results strongly suggest that existence of an avian homologue of the MAF-like activity.

Animals↗
PubMed1994

A class I cDNA from SPAFAS line-11 chickens.

A chicken MHC class I (B-F) cDNA from SPAFAS line 11 embryonic liver tissue was isolated and characterized by nucleotide sequencing. Comparing this sequence with previously described B-F cDNAs highlights clustered nucleotide substitutions in exon 3, encoding amino acids located on the alpha-helical region of the alpha 2 domain.

Amino Acid Sequence↗
PubMed1993

Identification of class II major histocompatibility complex polymorphisms predicted to be important in peptide antigen presentation.

Chickens of the B2, B5, B15, B19, and B21 B-congenic haplotypes differ in disease resistance. Complementary DNA from B-congenic chicken strains have been analyzed for allelic diversity of expressed Class II MHC genes. The predicted amino acid sequences of eight genes from five haplotypes were subjected to Wu-Kabat variability analysis. The B-L gene polymorphic regions and conserved regions are highly similar to the human leukocyte antigen Class II genes. Therefore, the present analysis reveals candidate polymorphisms important in determining the spectrum of antigenic peptides presented to T helper cells, and allelic differences possibly important in resistance to avian disease.

Animals↗
PubMed1987

Avian thyroid isthmus.

An avian equivalent of the mammalian thyroid isthmus appeared in thiouracil-treated (.1% in feed nd hatching to 6 and 8 weeks of age) chickens. In two experiments in which chickens were fed a diet containing thiouracil, thyroid tissue was found connecting the thyroid glands. Histological examination of the connecting tissue revealed that it was of the same cellular composition as the thyroid glands.

Animals↗
PubMed1987

Avian thyroid isthmus.

An avian equivalent of the mammalian thyroid isthmus appeared in thiouracil-treated (.1% in feed from hatching to 6 and 8 weeks of age) chickens. In two experiments in which chickens were fed a diet containing thiouracil, thyroid tissue was found connecting the thyroid glands. Histological examination of the connecting tissue revealed that it was of the same cellular composition as the thyroid glands.

Animals↗
PubMedDate not supplied

Identification of Rfp-Y (Mhc-like) haplotypes in chickens of Cornell lines N and P.

Two strains of chickens selected for differential Marek's disease (MD) resistance or susceptibility were studied for the presence of the recently described Rfp-Y major histocompatibility complex (Mhc-like) haplotypes. MD resistant chickens from line N were fixed for the classical Mhc B21 haplotype, whereas MD susceptible line P chickens were fixed for the B19 haplotype. The Rfp-Y haplotypes were identified by restriction fragment polymorphism (RFP) analysis using enzymes and Mhc probes for B-G, B-L beta II, and B-FIV. In addition an Rfp-L beta III clone was developed that differentiated Rfp-L beta from B-L beta genes. Three Rfp-Y haplotypes, defined for both class I and class II Mhc-like loci, were identified in line N (Rfp-Y5, Rfp-Y7, and Rfp-Y8) and in line P (Rfp-Y5, Rfp-Y8, and Rfp-Y9), respectively. The Rfp-Y7, Rfp-Y8, and Rfp-Y9 haplotypes have not been described previously. The Rfp-Y5 haplotype was most frequent (0.70) in line N, but existed in low frequency (approximately 0.04) in line P; the Rfp-Y9 haplotype was most frequent in line P (0.63), but was absent in line N. The Rfp-Y haplotypes-segregated in a Mendelian fashion in each line based on analysis of progeny from Rfp-Y heterozygous matings. The frequency of recombination between the Rfp-Y F and L loci was estimated to be less than 0.25%.

Animals↗
PubMedDate not supplied

The effects of F strain Mycoplasma gallisepticum, Mycoplasma synoviae, and the dual infection in commercial layer hens over a 44-week laying cycle when challenged before beginning of lay. II. Egg size distribution.

In each of two trials, 160 commercial pullets were separated into four treatments with four replicates of 10 chickens in each treatment. Forty pullets were designated as controls and received no inoculation; 40 pullets received F strain Mycoplasma gallisepticum (FMG); an additional 40 pullets received Mycoplasma synoviae (MS); and the final 40 pullets were inoculated with both FMG and MS (dual). All inoculations occurred at 10 wk of age. Eggs from all treatments were collected daily, Monday-Thursday, and individually weighed. No significant difference was observed among the treatments for percentages of jumbo, extra-large, medium, small, peewee, or undergrade eggs. As a percentage of eggs laid for the 4 days of each week over the 44-wk laying cycle of each trial, the FMG hens laid significantly fewer large size eggs (43.2%) as compared with either controls (51.17%) or dual-infected hens (49.95%). No significant difference was found in percentage of large eggs laid by FMG hens when compared with MS hens.

Animal Husbandry↗
PubMedDate not supplied

Effects of age at inoculation and induced molt on the recovery of Mycoplasma gallisepticum from layer chickens.

An experiment was conducted to determine the effects of age at inoculation and induced molt on the reisolation of Mycoplasma gallisepticum (MG) from commercial leghorn hens that had been eyedrop-inoculated with F strain MG at either 10 or 66 wk of age. Chickens were maintained in biological isolation units from 10 wk of age through 78 wk of age. At 70 wk of age (premolt), hens were swabbed, cultured for MG, and molted. Swabs were taken both at the end of molt (postmolt [74 wk]) and again 4 wk later (postmolt+4 [78 wk]). A significant (P < or = 0.05) decrease in MG isolations was observed in the postmolt swabs as compared with the premolt swabs of hens inoculated at either 10 or 66 wk of age. A significant (P < or = 0.05) increase in isolations was observed in the postmolt+4 swabs as compared with the postmolt swabs of hens inoculated at either 10 or 66 wk of age. For the hens inoculated at 10 wk, no significant difference was found in premolt as compared with postmolt+4 MG isolations; however, for hens inoculated at 66 wk, a significant (P < or = 0.05) decrease was observed between premolt and postmolt+4 isolations. Significantly (P < or = 0.05) fewer MG isolations were obtained from the premolt swabs of hens inoculated at 10 wk as compared with hens inoculated at 66 wk. No significant difference in MG isolations was observed in either the postmolt or postmolt+4 swabs between hens inoculated at either 10 or 66 wk.

Aging↗
PubMedDate not supplied

The effects of F strain Mycoplasma gallisepticum, Mycoplasma synoviae, and the dual infection in commercial layer hens over a 44-week laying cycle when challenged before beginning of lay. I. Egg production and selected egg quality parameters.

In each of two trials, 160 commercial pullets were separated into four treatments with four replicates of 10 chickens in each treatment. Forty pullets were designated as controls and received no inoculation; 40 other pullets received F strain Mycoplasma gallisepticum (FMG); an additional 40 pullets received Mycoplasma synoviae (MS); and the final 40 pullets were inoculated with both FMG and MS (dual). Hen-day egg production, egg weight, eggshell strength, Haugh unit score, pimpling incidence, and blood/meat spot incidence were monitored and recorded in each trial through an entire laying cycle. No significant difference was observed among the treatments for hen-day egg production, egg weight, eggshell strength, or Haugh unit scores. Significant differences were observed for pimpling incidence among controls (1.63%), Mycoplasma gallisepticum (MG)-infected (2.09%), and dual-infected hens (2.41%). A significant difference in blood/meat spot incidence was observed between MG-infected hens (0.27%) and dual-infected hens (0.45%). Histopathologic examination of the ovary and all segments of the oviduct revealed no significant differences among the treatments. These results suggest that the majority of the hen reproductive tract functions similarly in FMG-vaccinated, MS-infected, or dual-infected hens as compared with Mycoplasma-clean hens.

Animals↗
PubMedDate not supplied

Effect of drinking water containing ammonium chloride or sodium bicarbonate on Mycoplasma gallisepticum isolation in experimentally infected broiler chickens.

In each of three trials, 150 day-old broiler chicks were eyedrop inoculated with 0.04 ml of high-passage F strain Mycoplasma gallisepticum (MG) and housed in biological isolation units at 10 chicks per unit. At 4 wk of age, 50 chickens were designated as controls and remained on tap water (pH 7.30), 50 chickens were provided tap water containing 0.63% ammonium chloride (NH4Cl, pH 6.91), and 50 chickens were provided tap water containing 1.26% sodium bicarbonate (NaHCO3, pH 8.17). Fluids were supplied for ad libitum consumption. At 5 wk of age, all chickens were swabbed from the choanal cleft for MG isolation and bled from the left cutanea ulnea vein for pH determination. As a percent of total swabs obtained, significantly fewer chickens that consumed water containing NH4Cl (38.3%) were positive for MG by culture compared with either the NaHCO3 group (61.3%) or the control group (67.6%). Nonmycoplasmal swab contamination was significantly higher for chickens that consumed water containing NH4Cl (59.7%) compared with either controls (31.8%) or NaHCO3-treated chickens (38.7%). When contaminated cultures were discarded, MG isolations from the tap water group were not significantly different from MG isolations from either the NH4Cl or NaHCO3 group. However, MG isolations from the NH4Cl group (95%) were significantly less compared with the NaHCO3 group (100%). Mortality was significantly higher in chickens that consumed water containing NaHCO3 (8.7%) compared with either controls (1.3%) or the NH4Cl-treated chickens (0.7%). Blood pH values were lower for the NH4Cl group (7.927), higher for the NaHCO3 group (8.093), and intermediate for controls (8.035). Results of this study suggest that water containing NH4Cl hinders the bacteriological recovery of MG from the choanal cleft.

Ammonium Chloride↗