Clonal anergy of CD117+chB6+ B cell progenitors induced by avian leukosis virus subgroup J is associated with immunological tolerance.

BACKGROUND: The pathogenesis of immunological tolerance caused by avian leukosis virus subgroup J (ALV-J), an oncogenic retrovirus, is largely unknown. RESULTS: In this study, the development, differentiation, and immunological capability of B cells and their progenitors infected with ALV-J were studied both morphologically and functionally by using a model of ALV-J congenital infection. Compared with posthatch infection, congenital infection of ALV-J resulted in severe immunological tolerance, which was identified as the absence of detectable specific antivirus antibodies. In congenitally infected chickens, immune organs, particularly the bursa of Fabricius, were poorly developed. Moreover, IgM-and IgG-positive cells and total immunoglobulin levels were significantly decreased in these chickens. Large numbers of bursa follicles with no differentiation into cortex and medulla indicated that B cell development was arrested at the early stage. Flow cytometry analysis further confirmed that ALV-J blocked the differentiation of CD117+chB6+ B cell progenitors in the bursa of Fabricius. Furthermore, both the humoral immunity and the immunological capability of B cells and their progenitors were significantly suppressed, as assessed by (a) the antibody titres against sheep red blood cells and the Marek's disease virus attenuated serotype 1 vaccine; (b) the proliferative response of B cells against thymus-independent antigen lipopolysaccharide (LPS) in the spleen germinal centres; and (c) the capacities for proliferation, differentiation and immunoglobulin gene class-switch recombination of B cell progenitors in response to LPS and interleukin-4(IL-4) in vitro. CONCLUSIONS: These findings suggested that the anergy of B cells in congenitally infected chickens is caused by the developmental arrest and dysfunction of B cell progenitors, which is an important factor for the immunological tolerance induced by ALV-J.

Congenital cerebellar dysplasia in White Leghorn chickens (Gallus gallus domesticus).

Congenital cerebellar anomalies have been rarely reported in birds. We examined cerebellums with disorganized folia from seven specific-pathogen-free White Leghorn chickens (Gallus gallus domesticus). Islands of heterotopic cortex were distributed from the deeper cortices to the medulla in the cerebellum. The characteristic lesions were composed of randomly admixed components of the cerebellar cortex, including Purkinje cells, a molecular layer and granular cells. Immunofluorescent analysis revealed Purkinje cells with haphazardly extended dendrites and a lack of Bergmann's glial fibres in the foci. Chicken parvovirus, Aino virus and avian retrovirus were not detected in the affected birds by polymerase chain reaction. This is the first report of cerebellar dysplasia in chickens possibly caused by a genetic abnormality.

First report of polymelia and a rudimentary wing in a Nigerian Nera black chicken.

A case of polymelia with a rudimentary wing is described in an eight-week-old Nera black chicken (Gallus domesticus). It is a rare disorder with chromosomal aberrations, which are associated with congenital limb malformations. The condition was observed during routine physical examination of a flock of 2000 poultry birds in the month of February 2008 in Ibadan, Nigeria. After physical examination, the bird was found to have two extra well-developed legs, which were shorter than the normal legs. These extra legs were also found to be non-functional. Similarly, a rudimentary wing, which was highly vestigial, was found on the left lateral side of the bird very close to the cloaca. The bird died at the age of eight weeks. This is the first reported case of polymelia with a rudimentary wing in a domestic chicken in Nigeria.

Congenital intestinal incarceration in broiler chickens.

The present work describes specific congenital intestinal accidents found in commercial broiler chickens where the affected individuals have their intestinal loops translocated outside the abdomen. These anomalies have been observed in many embryos that failed to hatch, in newly hatched chicks, as well as in broilers at various stages of growth. It appears that these lesions stem from incomplete closure of the abdominal cavity during the last stages of embryonic development.

Congenital cataract in 1-day-old French Mulard ducklings.

Ocular opacity, associated with reluctance to move and inability to feed properly, was observed in approximately 1% of all newly hatched females from several related flocks of Mulard ducks. A 5-week follow-up study of 10 1-day-old affected females was performed, and they were compared with 10 control animals. Clinical, ocular and ultrasonographic examinations, and a complete necropsy of two animals per group with histological examination of the eye, were performed weekly. A bilateral immature cortical anterior cataract was diagnosed at ocular examination and confirmed by ultrasonography in affected ducks. Dyscoria was occasionally observed in affected animals. Severe cataract, with Morgagnian globules, severe anterior fibre liquefaction and disorganization were observed by photonic microscopy. No retinal or choroidal lesions were observed. No progression or repair of ultrasonographic and microscopic lesions could be detected during the 5 weeks of examination. The female predisposition for the ocular lesions suggests a congenital sex-linked recessive cataract.

Heterophil function and resistance to staphylococcal challenge in broiler chickens naturally infected with avian leukosis virus subgroup J.

Avian leukosis virus subgroup J has a high tropism for myeloid lineage cells and frequently induces neoplastic transformation of myelocytes. The impact of congenital avian leukosis virus subgroup J infection on the function of circulating heterophils and susceptibility to staphylococcal infection was investigated. Six-week-old broiler chickens negative for exogenous avian leukosis viruses or congenitally infected with avian leukosis virus subgroup J were inoculated intravenously with 10(6) colony-forming units of Staphylococcus aureus, and pre- and postinoculation heterophil function was assessed. All chickens developed a leukocytosis with heterophilia after inoculation, but total leukocyte and heterophil counts were significantly higher in leukosis-negative chickens than in virus-infected chickens. Tenosynovitis was more severe in leukosis-negative chickens, and 2/10 (20%) of the virus-infected chickens had no histologic evidence of tenosynovitis. Osteomyelitis in the tibiotarsus or tarsometatarsus developed in 5/10 (50%) of the chickens in each group. S. aureus was recovered from the hock joint of 6/10 (60%) of the chickens in each group. Heterophils from all chickens exhibited similar phagocytic ability pre- and postinoculation. Heterophils from virus-infected chickens exhibited less bactericidal ability preinoculation than did heterophils from leukosis-negative chickens. However, postinoculation bactericidal ability was similar in both groups. Avian leukosis virus subgroup J provirus was present in heterophils isolated from congenitally infected chickens. Heterophils isolated from broiler chickens congenitally infected with avian leukosis virus subgroup J exhibit no significant functional deficits, and infected and uninfected chickens exhibit similar susceptibility to staphylococcal infection.

The half-life of duck hepatitis B virus supercoiled DNA in congenitally infected primary hepatocyte cultures.

The transcriptional template for duck hepatitis B virus (DHBV) replication is believed to be the supercoiled covalently closed circular (CCC) molecule. DHBV CCC DNA can be amplified at least 50-fold in acutely and congenitally infected hepatocyte cultures but is normally maintained at a constant copy number in vivo infections. Here we describe experiments to determine the half-life of DHBV CCC DNA in congenitally infected hepatocyte cultures using both direct and indirect labeling of DHBV CCC DNA with the DNA labeling agent 5-bromo 2-deoxyuridine (BrUdR). Direct labeling of DHBV CCC DNA with BrUdR generated a very stable molecule with no calculable half-life. For indirect labeling experiments, hepatocytes were first cultured for 5 days in the absence of BrUdR to generate a pool of unlabeled DHBV CCC DNA, in then BrUdR was added to the culture medium. By following the fate of the pool of unlabeled CCC DNA in the cultures over time we calculated the half-life of DHBV CCC DNA to be 3 and 5 days in two separate experiments. This result suggests that there is a requirement for continuous amplification of DHBV CCC DNA to maintain a persistent chronic infection.

Hereditary congenital baldness: a sex-linked trait in the domestic fowl.

Congenital baldness in the domestic fowl is a genetic condition in which small irregular skin areas are devoid of down feathers (and later definitive feathers) over one or both eyes and/or the center of the head. In this study, the expression of congenital baldness was quite variable and ranged in size from a few follicles to areas as large as 10 mm2. The area over the right eye and the center of the head was more frequently involved than was the area over the left eye. This condition was inherited as sex-linked recessive. The symbol ba was assigned to the gene, and it was shown to be linked to the sal locus by 7.6 to 8.2 crossover units. An unusual feature was that 5% to 13% of heterozygous males exhibited the trait.

Vertical transmission of reticuloendotheliosis virus in breeder turkeys.

Epizootiological studies were conducted on a commercial turkey breeder flock naturally infected with nondefective reticuloendotheliosis (RE) virus. Although RE virus was isolated from 27 (46%) of the 59 hens studied, only 4 of the 45 hens tested transmitted RE virus to progeny during a 6-week observation period and the overall transmission rate was 1.8%. The transmitter hens were of two types: three hens were consistently viremic and antigenemic and lacked antibody; one hen was viremic but lacked detectable viral antigen and possessed antibody. Toms appeared to play no role in vertical transmission of the infection. Of several tests evaluated for detection of transmitter hens, the direct enzyme-linked immunosorbent assay on albumen was probably best, since it detected three of four transmitter hens, detected relatively few nontransmitter hens, and had the best consistency of any test. No significant differences in hatchability were found between eggs from viremic and non-viremic hens. These findings can be utilized in the development of programs for eradication of RE virus from turkey breeding flocks.

A sequential histologic and immunohistochemical study of duck hepatitis B virus infection in Pekin ducks.

Twenty-nine Pekin ducks were inoculated with duck hepatitis B virus (DHBV), DHBV-free serum, or saline at 1 day of age. Congenitally DHBV-infected ducks were also studied. Ducks were killed periodically during a 92-week study and examined histologically and immunohistochemically to assess liver and extrahepatic inflammation and to detect and characterize DHBV core antigen tissue distribution. DHBV infection produced an asymptomatic but persistent DHBV viremia in all ducks associated with a mild to moderate transient hepatic inflammation apparent at 3 to 6 weeks post-inoculation and waning afterwards. DHBV core antigen was detected in hepatocyte cytoplasm at 1 week post-inoculation, and by 3 weeks post-inoculation scattered pancreatic acinar and islet cells also contained viral antigen. Small numbers of mononuclear cells in the splenic white pulp also contained viral antigen. Viral antigen persisted in all of these tissues throughout the duration of the experiment. No inflammation or tissue injury was detected in any of the extrahepatic tissues during the course of DHBV infection. One DHBV-injected duck developed a hepatocellular carcinoma at 88 weeks of age. Isolated patches of neoplastic hepatocytes contained cytoplasmic DHBV core antigen. The results of this study indicate that DHBV, like mammalian hepadnavirus, is capable of producing a persistent infection of the liver and several extrahepatic tissues and suggest that persistent infection may be associated with the development of hepatocellular carcinoma.

Genetic cellular resistance to subgroup E avian leukosis virus in slow-feathering dams reduces congenital transmission of an endogenous retrovirus encoded at locus ev21.

The gene ev21, which encodes an infectious endogenous subgroup E avian leukosis virus (ALV-E), designated EV21, is closely linked to the sex-linked, slow-feathering (SF) gene K. To address the relationship between congenital transmission of EV21 and host susceptibility to ALV-E infection, SF roosters that were heterozygous for the dominant gene for susceptibility to ALV-E were mated with ev-negative rapid-feathering (RF), subgroup E-resistant dams to produce SF and RF progeny. The SF female progeny that were heterozygous ALV-E susceptible were viremic at hatch and, when mature, consistently shed the ALV group-specific antigen, p27, in the egg albumen they produced. In contrast, SF females that were homozygous ALV-E resistant were neither viremic at hatch nor shedders of ALV p27. Infectious ALV-E assays of progeny from susceptible and resistant SF dams confirmed that maternal cellular resistance to ALV-E limited congenital transmission of EV21. It is proposed that, in progeny, immunologic tolerance toward exogenous ALV infection due to congenital transmission of antigenically related endogenous viruses may be abrogated by selection for cellular resistance to ALV-E in SF lines used as female parents of feather-sexed crosses.

Influence of congenital transmission of endogenous virus-21 on the immune response to avian leukosis virus infection and the incidence of tumors in chickens.

After contact exposure to Strain RPL-40 avian leukosis virus-infected hatchmates, a dilatory neutralizing antibody response and prolonged RPL-40 viremia was found among most pullets that were congenitally infected with endogenous virus 21 (EV21). Conversely, most of the hatchmates that were not congenitally infected seroconverted within 10 wk after exposure to Strain RPL-40 virus. Compared with noncongenitally infected hatchmates, EV-21 infection-induced tolerance to pathogenic avian leukosis viruses was reflected in a significantly higher incidence of lymphomas in congenitally infected hens. The rate of seroconversion and the incidence of RPL-40 virus-induced tumors among noncongenitally infected daughters from slow-feathering dams homozygous resistant to EV were similar to those found among daughters of rapid-feathering dams that lacked genetic locus ev21. Results suggest that selection for resistance to EV may eliminate tolerance toward oncogenic field strains of avian leukosis viruses and may improve the performance of progeny from a feather-sex cross.

Selective shedding and congenital transmission of endogenous avian leukosis viruses.

Shedding and congenital transmission of endogenous avian leukosis viruses were studied in viremic White Leghorn hens exogenously infected with viruses with endogenous long terminal repeats (LTRs) and in four semicongenic lines of hens that naturally express infectious endogenous viruses (EVs). Relatively high titers of infectious virus EV7 (encoded at locus ev7), Rous-associated virus-0 (RAV-0), and recombinant 882/-16 RAV-0 were detected in blood cells and sera from exogenously infected hens, but marked differences were noted in the incidence of congenitally infected progeny. In enzyme immunoassays that detect viral group-specific antigen, little or no p27 was detected in albumens from dams infected with RAV-0. However, hatchmates infected with either EV7 or recombinant 882/-16 RAV-0, which was constructed with an RAV-0 LTR, shed high titers of p27. Similarly, semicongenic hens that expressed RAV-0 (EV2) (encoded at locus ev2) shed little or no p27 into albumens, but hens that harbored ev10, ev11, and ev12 shed high titers of p27. A slower electrophoretic mobility of p27, considered to be characteristic of EVs that are restricted in congenital transmission, was not associated with low levels of shedding or congenital transmission; p27 from other EVs and p27 from an avian leukosis virus field strain, all of which are shed at high levels, had mobilities identical to that of p27 from RAV-0. Although shedding and congenital transmission appear to be controlled by the viral genome, there was no correlation between low efficiency of shedding or congenital transmission and endogenous LTR or p27 sequences.

Gall bladder anomaly in a young chicken.

A multi-cystic gall bladder was observed at necropsy in a 7-week-old broiler cockerel. Cystic lumina contained multiple elongated papillary epithelial projections and plicae composed of epithelium and lamina propria, abutting normal lining epithelium.

The effect of experimental turkey embryo infection with Mycoplasma meleagridis on weight, weight gain, feed consumption, and conversion.

Turkey poults were obtained from an earlier trial where hatchability performance of a group of embryos experimentally infected with Mycoplasma meleagridis [MM(+)] was compared with that of a group of uninfected cohorts [MM(-)]. In the present trial, post-hatch production parameters compared were weight, weight gain, feed consumption, feed conversion, culling, and mortality. Both toms and hens were monitored for 16 weeks, and a group of randomly selected toms was monitored for 22 weeks. Final liveweights and dressweights of hens were compared at 17 weeks, and those of the toms were compared at 23 weeks. Hens showed no significant (P less than 0.05) differences in the measured parameters during the 16-week period, nor did the initial population of toms, except in weight gain during the final period (weeks 12-16) and in final weight at week 16, which were significantly (P less than 0.05) greater in the MM(+) toms than in their MM(-) cohorts. Dressweights at slaughter of MM(+) hens were significantly greater than those of MM(-) hens, but liveweights of hens at slaughter and both liveweights and dressweights of toms at slaughter did not differ significantly. This inability of MM(-) turkeys to demonstrate a comparative advantage over MM(+) birds agrees with an earlier trial (4), in which MM(+) poults had weights superior to those of MM(-) cohorts during the first 3 to 4 weeks of life (4). These data indicate that the theory of superior performance in association with MM(-) birds must be reevaluated before the benefits derived from an M. meleagridis eradication program can be measured.