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D L Ewert

Publications and source records attributed to D L Ewert.

At least 55 records · Page 3Linked to original sources
PubMed1990

In ovo infection with the avian retrovirus RAV-1 leads to persistent infection of the central nervous system.

The ability of an avian retrovirus to cause central nervous system (CNS) disease was investigated in chickens infected in ovo with Rous associated virus-1. Viral envelope and core proteins and mature virions were found throughout CNS parenchyma, with the highest amounts localized in the granular layer of the cerebellum, in blood vessel endothelium, and the choroid plexus. This distribution was established by the time of hatching and persisted throughout the 14 weeks of observation. The highest levels of integrated proviral DNA and viral mRNA, were present in the cerebellum, consistent with the distribution of viral antigens. Mononuclear cell infiltrates were evident throughout the CNS, consistent with an inflammatory process. However, demyelination or vacuolar changes, as observed in other retroviral-induced CNS diseases, were not detected. Clinical symptoms of progressive neurologic dysfunction, i.e., weakness or paralysis of the hindlimbs, imbalance, and ataxia, were present in 7 of 38 infected chickens before termination of the experiment at 14 weeks posthatch. Viral antigens or lymphocyte infiltration were not detected in peripheral nerves. These findings suggest that the avian system may provide a valuable model to analyze the mechanisms governing retroviral induced CNS disease.

Animals↗
PubMed1989

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.

Animals↗
PubMed1989

Muscle afferents and the neural dynamics of limb position and velocity sensations.

Today muscle spindles are thought to be the primary receptor responsible for limb position and velocity. A mathematical model describing the muscle spindle's complex dynamical behavior was developed recently by Hasan. Other researchers have observed neuronal firing in the cortex of primates when muscles surrounding a joint have been passively stretched by joint movement. The purpose of this paper is to apply the muscle spindle model to a "two-muscle joint" and quantitate the resultant firing rates for various joint positions and velocities. With this information insights into the required neuronal dynamics for extracting position and velocity information from muscle spindles can be gained.

Afferent Pathways↗
PubMed1986

Susceptibility of avian B lymphocytes to retroviral infection parallels that of fibroblasts.

The ability of conventional virus receptors to mediate infection and transformation of immature B cells by the avian leukosis virus (ALV) was analyzed in chimeric chickens whose bursa of Fabricius contained a mixture of B cells from subgroup A virus receptor-positive and -negative chickens. The data indicate that factors that determine resistance of fibroblasts to ALV infection also apply to bursal cells and that other receptors expressed by B cells, i.e., antigen or mitogen receptors, do not initiate infection or transformation, at least not independent of conventional virus receptors.

Animals↗
PubMed1985

Ablation of humoral immunity in 15I5 x 72 chickens is not predisposing to the formation of subgroup G virus-induced distal sarcomas.

Clone (cl.) 85 infection of 15I5 x 72 chickens at 4 weeks posthatch results in a lower frequency of distal sarcomas than does Prague (Pr)-B infection. As higher titers of virus-neutralizing antibody are generated in the cl.85-infected chickens, the possibility was addressed in the present study that the low frequency of cl.85-induced distal sarcomas is a direct consequence of the strong neutralizing response. Our observations indicate that ablation of humoral immunity by embryonic bursectomy does not serve to increase this frequency, implying that the antiviral humoral response is not required to limit formation of cl.85-induced distal sarcomas.

Animals↗
PubMed1985

Duck hepatitis B virus is tropic for exocrine cells of the pancreas.

Earlier observations had established that duck hepatitis B virus (DHBV) is tropic for pancreatic endocrine cells, including cells localized to islets and to acini. Because cells identifiable as endocrine represented only a minor fraction of the total acinar-associated, infected subpopulation, the possibility was addressed in the present study that this subpopulation also comprises exocrine cells. Fixed preparations of cells from pancreas of congenitally DHBV-infected young ducks were reacted in double immunofluorescence assay with anti-virus serum and either anti-avian pancreatic polypeptide (APP) serum, a probe for a major subclass of acinar-associated endocrine cells, or anti-chymotrypsin serum, a probe for exocrine cells. Approximately 2-5% of the cells in these preparations were viral antigen-positive, comprising a minor fraction positive for APP and a much larger fraction positive for chymotrypsinogen. The detection of the latter establishes that DHBV is tropic for exocrine cells.

Animals↗
PubMed1984

Sarcoma growth in 15I5 x 7(2) chickens infected with avian sarcoma viruses of subgroup B or G.

A comparative study was made of sarcoma growth in 15I5 x 7(2) chickens infected in the wing web at 4 weeks of age with strains of subgroup B or G avian sarcoma viruses. Infection with sarcoma viruses of either subgroup B or G resulted in the formation of progressive wing web sarcomas at the site of inoculation. The survival times of the subgroup G virus-infected chickens were generally at least twice as great as the survival times of the subgroup B virus-infected chickens, which averaged 6-9 weeks postinoculation. At 5 weeks postinfection, a significantly higher titer of virus neutralizing antibody was detected in the subgroup G virus-infected chickens. Necropsy indicated that a high percentage of subgroup B virus-infected chickens exhibited fibrosarcomas at sites distal to the primary wing web sarcomas, whereas only a small percentage of subgroup G virus-infected chickens exhibited distal sarcomas. The results further indicated that the viral env gene is a determinant of the pattern of distal sarcoma formation.

Animals↗
PubMed1984

Individual ev loci determine characteristic patterns of endogenous retroviral envelope antigen expression during lymphocyte maturation.

A comparative study of the expression of retroviral envelope antigen by T and B lymphocytes at different maturational stages was made with chickens typed for genomic ev loci. All lymphocyte subclasses from chf(-) chickens were negative for expression of retroviral envelope antigen. By contrast, cells of the lymphocyte lineage from all the chf(+) lines examined were positive for expression, with the levels of envelope antigen in the lymphoblasts exceeding the levels in the immature and resting cells. This pattern of lymphocyte expression was found in lines of chickens in which the expression of chf in fibroblasts was encoded by the ev 3, ev 6, or ev 9 loci. Plasma cells from those chf(+) lines possessing ev 6 expressed higher levels of envelope antigen than the lymphoblasts, an effect not observed with the chf(+) lines lacking ev 6.

Animals↗
PubMed1984

The B-L (Ia-like) antigens of the chicken. Lymphocyte plasma membrane distribution and tissue localization.

Specific antisera reacting with B-L (Ia-like) antigens were prepared by reciprocal immunization of animals from the congeneic lines CB and CC. The resulting antisera were tested either in direct or indirect immunofluorescence tests and stained 10-16% of peripheral blood cells (PBL). Of the B-L+ cells, 90% were B cells and 8% were T cells. After in vitro stimulation of PBL with ConA, 58% were B-L+ and 91% of these were T cells. B and T cells were defined by means of rabbit antisera raised against bursa and thymus cells made specific by absorption with the relevant tissues. Antigens determined by anti-B-L antisera, rabbit anti-bursa (ABS) and rabbit anti-thymus (ATS) sera showed an independent distribution on the membrane of PBL. The tissue distribution of B-L+ cells, defined by means of allo-antisera and monoclonal antibodies, was studied by direct and indirect immunofluorescence on sections of skin, liver, kidney and brain. In all organs, in addition to B cells and a small number of, presumably activated, T cells, macrophages and dendritic cells were positive. Notably, glia cells in the brain were also shown to express B-L antigen.

Animals↗
PubMed1984

Analysis of structural properties and cellular distribution of avian Ia antigen by using monoclonal antibody to monomorphic determinants.

In this report, we describe the analysis of Ia-like antigens in the chicken by using a monoclonal antibody (CIa-1) reactive with monomorphic determinants of the Ia-like (B-L) antigens. This antibody reacts with determinants on B cells in all avian species tested, but does not detect antigens on lymphocytes of representative mammals, reptiles, and amphibians. In addition to B cells, this antibody defines a subpopulation of the monocyte-macrophage series and reacts with mitogen-activated T cells. Immunochemical analysis indicates that the CIa-1 reactive antigen is a 65,000-dalton glycoprotein consisting of an alpha-chain of 32,000 daltons noncovalently bound to a beta-chain of 27,000 daltons. Under nonreducing conditions, the beta-chain migrates with slightly faster mobility. Two-dimensional gel analysis indicates that the beta-chain is the more heterogeneous of the two chains. Thus, the antigen detected by CIa-1 antibody is similar in cell distribution and structure to the murine Ia antigens and human DR antigens. During in ovo development, Ia+Ig- cells were not found in the yolk sac but were detected in the spleen, mesonephros, and bursa of 9-day embryos. Two populations of Ia+Ig- cells were identified in the bursa: 40 to 60% of the bursacytes, mostly larger cells, exhibited brighter immunofluorescence reactivity than the smaller bursacytes.

Animals↗
PubMed1983

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

Chickens segregating for the ev 3 locus were bred by backcross matings of line 6(3) to line 15B. Analysis of RAV-1-infected segregants indicated that inducibility of antibody reactivity for envelope glycoprotein group-specific determinants correlated with the absence of ev 3, whereas noninducibility correlated with the presence of ev 3. Since the ev 3(+) and ev 3(-) segregants possessed similar genetic backgrounds, these results provide direct evidence that the ev 3 locus determines the phenotype of noninducibility.

Animals↗
PubMed1983

Increased endogenous retroviral gene expression is a consequence of lymphocyte activation.

Plasma cells of line 151(5) chickens have been shown to express elevated levels of endogenous retroviral envelope glycoprotein (VEG), measured relative to levels expressed by both immature B cells and resting peripheral B lymphocytes. In this study we analyzed the relationship between peripheral blood lymphocyte (PBL) maturation and the level of VEG expression. A culture system was developed that would support maturation of pokeweed mitogen-activated peripheral B lymphocytes. As analyzed by cytofluorometry, both Ig+ and Ig- lymphoblasts present in the pokeweed mitogen-stimulated cultures expressed detectable levels of VEG in contrast to bursacytes and PBL. Similarly, Ig- blasts, which were present in concanavalin A-stimulated cultures of PBL and presumed to represent activated T cells, were also positive for the expression of VEG. Immature T cells, i.e., thymocytes, although negative by immunofluorescence analysis, expressed VEG at levels that were detectable by radioimmunochemical techniques. These results indicate that T cells as well as B cells constitutively express VEG, and that mitogenic activation of the resting lymphocyte induces an increase in VEG expression.

Animals↗