J. Robert Smyth

Effect of bursectomy on development of a spontaneous postnatal amelanosis

Abstract The delayed amelanotic (DAM) chicken line has been developed as a model of human vitiligo. The DAM line displays a spontaneous postnatal amelanosis which is characterized by the absence of normal pigmentation in emerging feathers. Bursectomy on the day of hatching significantly decreased the incidence and severity of amelanosis in birds examined 12 to 20 weeks after hatching. The results suggest that bursa-dependent lymphocytes play an important role in the development of delayed amelanosis in the DAM chicken.

The detection of melanocyte autoantibodies in the Smyth chicken model for vitiligo.

Smyth line (SL) chickens are phenotypically characterized by a posthatch depigmentation (vitiligo) of the feathers. The destruction of melanocytes in the feather follicle as well as in other tissues such as the choroid is genetically determined. Previous studies have shown that bursectomy or treatment with immunosuppressive agents decreases the incidence and severity of SL depigmentation (1). These observations implicate a role for the immune system, specifically the humoral component, in melanocyte destruction. In this study we show that there are circulating melanocyte-specific autoantibodies in the sera of depigmented SL chicks which are not present in sera from Light Brown Leghorn (LBL) control chicks. By immunoblots and by immunoprecipitation of radiolabeled melanocyte proteins, SL autoantibodies were shown to bind to multiple melanocyte proteins between 65 and 80 kDa. These proteins are not detected in SL fibroblasts. By immunoblotting, the incidence of autoantibodies for these 65- to 80-kDa proteins was determined to be 95% in depigmented SL chicks (n = 20), 0% in normally pigmented SL chicks (n = 8), and 5% in LBL chicks (n = 20). Melanocyte autoantibodies are detectable in the sera of affected chicks at or several weeks prior to the expression of depigmentation. This information, plus previously published data, implicate melanocyte autoantibodies in the depigmentary phenomenon of vitiligo observed in Smyth line chickens.

Persistence of abnormal melanocytes in immunosuppressed chickens of the autoimmune DAM line

SummaryThe delayed amelanotic (DAM) line of chickens (Gallus gallus) is characterized by the postnatal elimination of melanocytes from regenerating feathers and from the choroid. The process of elimination is accompanied by a massive infiltration of mononuclear leukocytes (MNL) into the supporting connective tissues. When surgically bursectomized at day of hatching, chickens from this lineage develop significantly less amelanosis of the feathers. We report here a histological analysis of regenerating feathers and choroids from bursectomized birds that maintained their plumage pigmentation. In the feathers we observed the presence of morphologically abnormal melanocytes in the absence of MNL infiltration. Choroids also contained abnormal melanocytes without MNL infiltration; however, we observed a few cases of amelanotic choroids with a few MNL. These findings indicate that melanocytes of pigmented birds are morphologically abnormal even in the absence of a bursa and in the absence of leukocytic infiltrates into regenerating feathers and possibly into the choroids. We conclude from these findings that the amelanosis in unbursectomized DAM birds is due to the response of the immune system to an abnormality in the melanocytes which, by itself, does not lead to depigmentation.

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 </= 0.05 and a 19-kb HindIII fragment, P </= 0.03). Methylation analyses revealed that the EV and endogenous avian retroviral (EAV) genes were methylated in both the SL and BL sublines of chickens; therefore, methylation does not appear to be responsible for the differences in the expression of vitiligo between SL and BL sublines. Expression of the EV genes correlated with the disease in vitiliginous SL101 birds and also in 5-Azacytidine-induced vitiliginous BL101 parental control chickens. Only one EV locus was detected in the unrelated Light Brown Leghorn control chickens (1q14) by in situ hybridization, whereas 3 EV loci were identified in SL101 and BL101 chickens (1p25, 2q26, and an unidentifiable microchromosome). Our observations indicate that EV genes may play a role in the induction of autoimmune vitiligo in the SL chicken model.

Autosomal albinism affects immunocompetence in the chicken

Immune responsiveness of three neonatal and juvenile phenotypes, determined by the albinotic C locus, was evaluated. The phenotypes included normally pigmented (C+/-), recessive white (c/ca), and completely amelanotic albinos (ca/ca). No differences in: (1) primary agglutinin levels directed against sheep red blood cells (SRBC) or Brucella abortus (BA), or (2) cell-mediated immunity, as estimated by in vivo mitogen stimulation, were associated with the albino phenotype. The significant suppression of secondary SRBC or BA agglutinins observed in albino chicks was limited and of questionable biological significance. Acquisition of passively transferred maternal BA agglutinins was significantly impaired in albino progeny irrespective of dam genotype. No differences in agglutinin levels were associated with dam genotype. In addition, uptake of yolk sac contents was retarded significantly in albino chicks at hatch. These data suggest that an impaired ability to absorb maternal antibody and not the capacity to mount an active immune response contributes to neonatal mortality in albino chicks.