Herpesvirus connection in the expression of autoimmune vitiligo in Smyth line chickens.

The Smyth line (SL) chicken is an animal model for human vitiligo, a common acquired depigmentary disorder affecting about 1-2% of people worldwide. The vitiligo-like depigmentation in SL chickens typically develops when the birds are between 6 and 14 weeks of age and may affect 70-95% of hatch mates. The development of SL vitiligo is considered to depend on two interacting components, namely an inherent melanocyte defect and an autoimmune reaction to melanocytes. Recently, a role for an environmental factor in the expression of vitiligo was suggested by the observation that only 10% of SL chicks imported from the University of Massachusetts (UM) and reared in isolation at biosecurity level 2 (BSL 2) at the University of Arkansas (UA) exhibited vitiligo. Following further assessment of environmental differences between UA and UM SL chickens, three environmental factors that may have influenced the expression of SL vitiligo were identified. Included were housing condition, status of Mycoplasma synoviae infection, and turkey herpesvirus (HVT) vaccination status. Studies were subsequently conducted at UA and UM to assess the role of these environmental factors in the expression of SL vitiligo. M. synoviae infection was not found necessary for vitiligo expression in SL chickens. However, HVT emerged as a strong candidate for an important environmental factor in SL vitiligo. The connection between HVT and SL vitiligo was confirmed for both BSL 2 and conventional housing. Therefore, the observations reported here suggest a strong causative link between HVT infection and SL vitiligo.

Molecular characterization of the Smyth chicken sublines and their parental controls by RFLP and DNA fingerprint analysis.

The Smyth line (SL) chicken, a model for autoimmune human vitiligo, is characterized by a spontaneous posthatch epidermal pigment loss (vitiligo). Even though the immunological and morphological changes accompanying the vitiligo process have been well studied, the genetics of this phenomenon remains elusive. The SL lines have been maintained by nonpedigreed matings since their inception, and therefore, the inbreeding status is unknown. The present study was designed to provide an estimate of the inbreeding coefficients and the molecular genetic profiles of the SL sublines, each homozygous for a different MHC haplotype and their MHC-matched parental control (BL) sublines. The DNA fingerprint analysis revealed that there is a moderate level of inbreeding within the SL and BL parental sublines. Of the two SL sublines studied, SL101 had the highest level of inbreeding (0.948). Similarly, its parental control line (BL101) was more inbred than the parental subline of SL102 (BL102). The very high level of similarity between the SL sublines and their respective parental control lines is shown further by the similarity index (SI) estimates (SI between SL101 and BL101 was 0.949 and that between SL102 and BL102 was 0.932). Restriction fragment length polymorphism (RFLP) analysis of the endogenous viral genes (avian leukosis virus subgroup E, ALVE) showed that five ALVE-related BamH1 fragments were present in the SL101 and four in SL102 sublines, whereas the parental BL101 and BL102 sublines had five and six fragments, respectively. SL101 and SL102 shared two fragments, but the frequencies were different. Similarly, BL101 and BL102 shared two fragments. SL101 and BL101 shared three fragments, and SL102 and BL102 also shared three fragments.

Identifying susceptibility genes using linkage and linkage disequilibrium analysis in large pedigrees.

Linkage and linkage disequilibrium tests are powerful tools for mapping complex disease genes. We investigated two approaches to identifying markers associated with disease. One method applied linkage analysis and then linkage disequilibrium tests to markers within linked regions. The other method looked for linkage disequilibrium with disease using all markers. Additionally, we investigated using Simes' test to combine p-values from linkage disequilibrium tests for nearby markers. We applied both approaches to all replicates of the Genetic Analysis Workshop 12 problem 2 isolated population data set. We reported results from the 25th replicate as if it were a real problem and assessed the power of our methods using all replicates. Using all replicates, we found that testing all markers for linkage disequilibrium with disease was more powerful than identifying markers that were in linkage with disease and then testing markers within those regions for linkage disequilibrium with the implementations that we chose. Using Simes' test to combine p-values for linkage disequilibrium tests on correlated markers seemed to be of marginal value.

A new recessive ametapodia mutation in the chicken (Gallus domesticus).

An apparently new mutation that is associated with abnormal limb development appeared in a strain of Light Brown Leghorn chickens. Mutants are characterized by the complete absence of the tarsometatarsals, while severely hypoplastic development of the metacarpals is also present. The phenotype of the new mutant (ametapodia-2) closely resembles ametapodia-1, described in 1967, but ametapodia-2 is inherited as an autosomal recessive (AMET*A), while ametapodia-1 was associated with an incompletely dominant gene (MP*A). Only heterozygous ametapodia-1 (MP*N/MP*A) were viable and able to reproduce, while homozygous ametapodia-2 mutants do not normally survive beyond 2-4 days of age. The shankless mutation (SHL*S) also reduces development of the metatarsal and metacarpal bones and has been shown to be associated with a pericentric inversion of chromosome 2. No obvious cytologic abnormality was apparent in ametapodia-2 birds, and offspring of a cross between AMET*A carriers and shankless birds were normal, indicating that the two mutations are not alleles. Ametapodia-1 (MP*A) was found to be linked to the rose comb locus (R) by 16 crossover units. Linkage test matings between AMET*A and (R*R) showed independent segregation, strongly suggesting that the mutation occurred at a relatively distant locus and therefore is probably not allelic to MP*A.

Analysis of the effect of endogenous viral genes in the Smyth line chicken model for autoimmune vitiligo.

The Smyth line (SL) chicken, an animal model for autoimmune human vitiligo, is characterized by a spontaneous posthatch pigment loss, determined to be the result of an autoimmune phenomenon. Because endogenous virus (EV) genes have been reported to be associated with a number of autoimmune diseases of human and animal models, we designed this experiment to investigate the role of EV in the SL vitiligo by using the complete sequence of Rous-associated virus-2 as a probe for EV. An F(2) resource population was developed by the matings of SL and parental control (BL) chickens. Linkage disequilibrium between vitiligo and EV was apparent (16.2-kb SacI fragment, P

5-azacytidine treatment induces autoimmune vitiligo in parental control strains of the Smyth line chicken model for autoimmune vitiligo.

The effect of 5-Azacytidine (5-AzaC) on melanization was examined in two sublines of the Smyth line (SL) chicken model for autoimmune vitiligo, in two MHC-matched vitiligo-susceptible but normally pigmented controls (BL), and in nonsusceptible controls (LBL). 5-AzaC was administered ip every 3 days from day of hatch to 18 weeks at levels of 1 or 3 mg/kg body wt. Both treatments increased (P < 0.01) the incidence of autoimmune vitiligo in BL controls. In contrast, treatment significantly depressed (P < 0.01) the expected high incidence of vitiligo in one SL subline, but not in the other. There were no apparent pigmentation changes in 5-AzaC-treated LBL controls. 5-AzaC had dose-dependent depressing effects (P < 0.01) on body and lymphoid organ weights. Histological and mitogen assay data suggest negative effects on lymphocyte number and function. The data show that 5-AzaC can initiate autoimmune disease in genetically susceptible but phenotypically normal individuals.

Immune response to sheep red blood cells in two Smyth line populations homozygous for different major histocompatibility complex haplotypes.

The Smyth line (SL) chicken is characterized by a high incidence of spontaneous, posthatch, selective destruction of melanocytes, caused by an autoimmune phenomenon. It has been shown that the MHC is associated with the development and severity of the disease. To clarify further the role of MHC haplotypes and other factors leading to an autoimmune response, mean antibody titers to SRBC were determined for 37-wk-old females from 2 SL sublines (SL101 and SL102), each homozygous for a different MHC haplotype, their MHC-matched parental control sublines (BL101 and BL102), and a normally pigmented control, LBL. Although total incidence of amelanosis is approximately the same for both SL sublines, amelanosis occurs earlier and is more severe in SL101 birds. Within sublines, chickens were further classified as to the extent of the feather amelanosis. Neither SL MHC subline had a mean SRBC titer that differed significantly from unrelated LBL controls. Although the secondary response of the two sublines differed from each other (P < .05), neither differed from its MHC-matched parental control; therefore, the differences in immune response appear to be largely MHC-related and not closely related to melanocyte destruction. When SRBC titers were related to amelanotic severity, no differences were found within the SL101 subline, although, SL102 birds that became amelanotic at a later age had a lower primary response to SRBC (P < .05) than the more severely affected group. Birds simultaneously producing both pigmented and amelanotic feather tissue had higher (P < .05) primary and secondary anti-SRBC titers than did the complete amelanotics.