Identification of T cells in early dermal lymphocytic infiltrates in avian scleroderma

Is low molecular weight hyaluronan an early indicator of disease in avian systemic sclerosis?

AIM OF THE STUDY

To further elucidate the pathogenesis of systemic sclerosis (SSc) an experimental avian model was used. The University of California at Davis line 200 (UCD-200) chickens spontaneously develop a SSc-like disease that has most features of human SSc with vascular effects, inflammation, autoimmunity, and fibrosis. The first signs of disease in UCD-200 chickens are swelling and ischemic lesions of the comb and the presence of a tissue containing high amounts of glycosaminoglycan hyaluronan (HA). The aim of this study was to evaluate inflammatory and fibrotic processes of the disease with regard to the molecular weight of HA.

MATERIAL AND METHODS

Comb biopsies from UCD-200 and healthy White Leghorn (WL) chickens, as controls, at different ages were studied with the histochemical localization of HA, hyaluronidase-1 (Hyal-1), cluster of differentiation 3, immunoglobulin Y, and collagen I and III. The molecular weight distribution of HA was estimated with gas-phase electrophoretic analysis.

RESULTS

At 2 days of age, HA was visualized in UCD-200 chickens at the dermal part of the comb with no simultaneous staining of Hyal-1. In adult UCD-200 chickens, the comb skin was almost totally devoid of HA compared to WL chickens of the same age. An increase of low molecular weight (LMW) HA was detected in comb tissue from UCD-200 at the age of 1 day, 1 week, 2 weeks, and 4 weeks, in contrast to adult animals.

CONCLUSIONS

An early inflammatory process involving LMW HA was confirmed as a possible profibrotic process. This indicates that HA might be an important participant in the early inflammatory events of SSc in UCD-200 chickens and that the disappearance of HA in skin predisposes to fibrosis.

Scleroderma Lung

The lungs are frequently involved in systemic sclerosis ('scleroderma'), a rare, disabling disease of unknown origin, characterised by skin thickening and Raynaud's phenomenon. The pathogenesis of scleroderma is complex, but signs and symptoms of excessive fibrosis, vasculopathy and inflammation are almost universally present. Dyspnoea in scleroderma patients can be due to chest wall tightening from skin thickening, pleural disease, cardiac involvement, myositis of intercostal muscles, or so-called scleroderma lung disease. Scleroderma lung disease encompasses vascular (pulmonary artery hypertension) or interstitial lung disease, or both. A comprehensive work-up is required to delineate the underlying cause of dyspnoea in a scleroderma patient, and to establish the contribution of each component to the symptoms. This should include a 6-minute walk test, pulmonary function testing, high-resolution thoracic CT scanning, ECG, echocardiography and, if pulmonary artery hypertension is suspected, right-heart catheterisation; bronchoalveolar lavage is optional. Lung disease in scleroderma contributes significantly to excess morbidity and early mortality, especially when diffusion capacity drops below 40% and/or forced vital capacity below 50%. However, recent clinical studies have unequivocally demonstrated that scleroderma lung disease is amenable to treatment with new vasodilatory drugs that target specific pathways involved in vasoconstriction, or with cyclophosphamide for interstitial lung disease. Uncontrolled studies have suggested that these therapies also have an impact on survival, but controlled studies with a long follow-up are needed to corroborate this point.

Avian models with spontaneous autoimmune diseases

Autoimmune diseases in human patients only become clinically manifest when the disease process has developed to a stage where functional compensation by the afflicted organ or system is not possible anymore. In order to understand the initial etiologic and pathogenic events that are generally not yet accessible in humans, appropriate animal models are required. In this respect, spontaneously developing models--albeit rare--reflect the situation in humans much more closely than experimentally induced models, including knockout and transgenic mice. The present chapter describes three spontaneous chicken models for human autoimmune diseases, the Obese strain (OS) with a Hashimoto-like autoimmune thyroiditis, the University of California at Davis lines 200 and 206 (UCD-200 and -206) with a scleroderma-like disease, and the amelanotic Smyth line with a vitiligo-like syndrome (SLV). Special emphasis is given to the new opportunities to unravel the genetic basis of these diseases in view of the recently completed sequencing of the chicken genome.

Differential effects of the immunosuppressant FK-506 on human ?2(I) collagen gene expression and transforming growth factor ? signaling in normal and scleroderma fibroblasts

OBJECTIVE

To investigate the effects of FK-506 on the expression of the human alpha2(I) collagen gene and transforming growth factor beta (TGFbeta) signaling in normal and scleroderma fibroblasts.

METHODS

The expression levels of type I procollagen protein and alpha2(I) collagen messenger RNA (mRNA) were analyzed by immunoblotting and Northern blotting, respectively. The promoter activities of alpha2(I) collagen gene and 3TP-Lux were determined by transient transfection assay. Interaction between TGFbeta receptor type I and FK-506 binding protein 12 (FKBP12) was evaluated by immunoprecipitation.

RESULTS

FK-506 did not affect the basal expression of type I procollagen protein or alpha2(I) collagen mRNA, but it significantly reduced the TGFbeta1-induced expression of type I procollagen protein and alpha2(I) collagen mRNA in normal fibroblasts. The effect of FK-506 was regulated posttranscriptionally, but not transcriptionally. In scleroderma fibroblasts, FK-506 significantly reduced the expression of type I procollagen protein and alpha2(I) collagen mRNA through posttranscriptional regulation, but not transcriptional regulation. FK-506 increased the basal activity of the 3TP-Lux promoter, but it did not affect the TGFbeta1-induced promoter activity in normal fibroblasts. In contrast, FK-506 did not affect the basal or the TGFbeta1-induced 3TP-Lux promoter activity in scleroderma fibroblasts. Furthermore, FKBP12, which protects TGFbeta receptor type I from ligand-independent activation by TGFbeta receptor type II, constitutively dissociated from TGFbeta receptor type I in scleroderma fibroblasts.

CONCLUSION

FK-506 inhibits alpha2(I) collagen gene expression by reducing the stability of mRNA without exhibiting its activation effect on TGFbeta signaling in scleroderma fibroblasts.

High-dose immunosuppressive therapy and autologous progenitor cell transplantation for systemic sclerosis

High-dose immunosuppressive therapy aimed at immunoablation, given together with autologous stem cell transplantation, has resulted in prolonged (>3 years) improvements of skin thickening and functional ability, together with a stabilization of pulmonary function in two-thirds of treated patients with severe systemic sclerosis. Transplant-related mortality occurred in 17% of the first cohort of 41 patients reported to the European Group for Blood and Marrow Transplantation, which included cases from the United States, but this figure has dropped to 8.7% in a recent retrospective analysis of 57 transplants performed in Europe. Similar outcomes were reported in multicentre studies from the United States of 19 patients, and from France of 12 patients, with improvements in skin scores and functional assessments, together with a stabilization of internal organ dysfunction. Based on the results of these phase I/II studies, multicentre prospective randomized trials are being planned or are in progress in Europe and the United States employing uniform patient entry criteria and outcome parameters. The aim of these studies is to compare the clinical benefits and safety of transplant regimens versus conventional chemotherapy in patients with severe systemic sclerosis who are at risk of life-threatening organ failure and premature mortality. Eligibility criteria include a diagnosis of diffuse systemic sclerosis of recent onset and major organ (heart, kidney, lungs) involvement according to predefined criteria. The prospective randomized trials address two issues related to the treatment of severe systemic sclerosis: is intensive immunosuppressive therapy superior to conventional therapy, and can self-tolerance be re-established?

Phase I/II trial of autologous stem cell transplantation in systemic sclerosis: procedure related mortality and impact on skin disease

BACKGROUND

Systemic sclerosis (SSc, scleroderma) in either its diffuse or limited skin forms has a high mortality when vital organs are affected. No treatment has been shown to influence the outcome or significantly affect the skin score, though many forms of immunosuppression have been tried. Recent developments in haemopoietic stem cell transplantation (HSCT) have allowed the application of profound immunosuppression followed by HSCT, or rescue, to autoimmune diseases such as SSc.

METHODS

Results for 41 patients included in continuing multicentre open phase I/II studies using HSCT in the treatment of poor prognosis SSc are reported. Thirty seven patients had a predominantly diffuse skin form of the disease and four the limited form, with some clinical overlap. Median age was 41 years with a 5:1 female to male ratio. The skin score was >50% of maximum in 20/33 (61%) patients, with some lung disease attributable to SSc in 28/37 (76%), the forced vital capacity being <70% of the predicted value in 18/36 (50%). Pulmonary hypertension was described in 7/37 (19%) patients and renal disease in 5/37 (14%). The Scl-70 antibody was positive in 18/32 (56%) and the anticentromere antibody in 10% of evaluable patients. Peripheral blood stem cell mobilisation was performed with cyclophosphamide or granulocyte colony stimulating factor, alone or in combination. Thirty eight patients had ex vivo CD34 stem cell selection, with additional T cell depletion in seven. Seven conditioning regimens were used, but six of these used haemoimmunoablative doses of cyclophosphamide +/- anti-thymocyte globulin +/- total body irradiation. The median duration of follow up was 12 months (3-55).

RESULTS

An improvement in skin score of >25% after transplantation occurred in 20/29 (69%) evaluable patients, and deterioration in 2/29 (7%). Lung function did not change significantly after transplantation. One of five renal cases deteriorated but with no new occurrences of renal disease after HSCT, and the pulmonary hypertension did not progress in the evaluable cases. Disease progression was seen in 7/37 (19%) patients after HSCT with a median period of 67 (range 49-255) days. Eleven (27%) patients had died at census and seven (17%) deaths were considered to be related to the procedure (direct organ toxicity in four, haemorrhage in two, and infection/neutropenic fever in one). The cumulative probability of survival at one year was 73% (95% CI 58 to 88) by Kaplan-Meier analysis.

CONCLUSION

Despite a higher procedure related mortality rate from HSCT in SSc compared with patients with breast cancer and non-Hodgkin's lymphoma, the marked impact on skin score, a surrogate marker of mortality, the trend towards stabilisation of lung involvement, and lack of other treatment alternatives justify further carefully designed studies. If future trials incorporate inclusion and exclusion criteria based on this preliminary experience, the predicted procedure related mortality should be around 10%.

Profiles of pulp infiltrating lymphocytes at various times throughout feather regeneration in Smyth line chickens with vitiligo

Smyth line (SL) chickens develop a spontaneous, autoimmune, posthatch loss of pigment cells (vitiligo) in regenerating feather tissue. Smyth line vitiligo (SLV) is associated with lymphocyte infiltrations prior to and throughout the development of the disorder. It was the purpose of this study to determine the type, relative amounts, and proportions of pulp-infiltrating lymphocytes at various times throughout the growth of regenerating feathers. Feathers were plucked from 8-week-old chickens with and without SLV. Feather pulp cell suspensions were prepared when the regenerating feathers were 2, 3, 4, and 6 weeks of age. Cells were fluorescently labeled using a panel of mouse monoclonal antibodies specific for chicken lymphocytes. Both T and B cells infiltrated the feather pulp of chickens with SLV. T cell levels remained elevated throughout the 6 weeks of feather growth, while B cell levels steadily declined to control levels over the same time. The pulp-infiltrating cells were primarily T cells with an alphabeta T cell receptor expressing the Vbeta1 gene (TCR2+). The ratio between CD4+ and CD8+ cells was 1.42 and 0.75 in 2- and 6-week-old regenerating feathers from chickens with autoimmune SLV, respectively. In non-vitiliginous chickens this ratio was always near 1. These data suggest that TCR2+ T cells play an important role in SLV. CD4+ cells may play a recruiting/activating role, whereas CD8+ cells may have cytotoxic activity specifically directed against melanocytes. Additionally, this is the first report demonstrating the infiltration of B cells into the feather pulp of vitiliginous chickens. These B cells may directly/indirectly contribute to melanocyte destruction in SLV.

Pathogenesis of scleroderma. Collagen

It is now evident that persistent overproduction of collagen and other connective tissue macromolecules results in excessive tissue deposition, and is responsible for the progressive nature of fibrosis in SSc. Up-regulation of collagen gene expression in SSc fibroblasts appears to be a critical event in the development of tissue fibrosis. The coordinate transcriptional activation of a number of extracellular matrix genes suggests a fundamental alteration in the regulatory control of gene expression in SSc fibroblasts. Trans-acting nuclear factors that bind to cis-acting elements in enhancer and promoter regions of the genes modulate the basal and inducible transcriptional activity of the collagen genes. The identity of the nuclear transcriptional factors that regulate normal collagen gene expression remains to be firmly established, and to date, no alterations in the level or in the activity of such DNA binding factors has been demonstrated in SSc fibroblasts. In addition to important interactions between fibroblasts and the extracellular matrix, cytokines and other cellular mediators can positively and negatively influence fibroblast collagen synthesis. Some of these signaling molecules may have physiologic roles, and their aberrant expression, or altered responsiveness of SSc fibroblasts to them, may result in the acquisition of the activated phenotype. The rapid expansion of knowledge regarding the effects of cytokines on extracellular matrix synthesis has led to an appreciation of the enormous complexity of regulatory networks that operate in the physiologic maintenance of connective tissue and which may be responsible for the occurrence of pathologic fibrosis. The ubiquitous growth factor TGF beta is the most potent inducer of collagen gene expression and connective tissue accumulation yet discovered. The expression of TGF beta in activated infiltrating mononuclear cells suggests a role for this cytokine as a mediator of fibroblast activation in SSc. Furthermore, the recognition that TGF beta is capable of inducing its own expression in a variety of cell types, coupled with the demonstration that a subpopulation of SSc dermal fibroblasts produces TGF beta, indicates the existence of a possible autocrine loop whereby lymphocyte-derived TGF beta in early SSc not only signals biosynthetic activation of fibroblasts in a paracrine manner, but autoinduces endogenous TGF beta production by the target fibroblasts themselves. Such an autocrine loop involving TGF beta may explain the persistent activation of collagen gene expression in SSc fibroblasts, and could be responsible for the progressive nature of fibrosis in SSc. Numerous other cytokines, as well as cell-matrix interactions, also modify collagen gene expression and can significantly influence the effects of TGF beta. Although their physiologic function in tissue remodeling or their involvement in abnormal fibrogenesis has not yet been conclusively demonstrated, the study of the biologic effects of these cytokines may provide important clues to understanding the pathogenesis of SSc, and to the development of rational drug therapy aimed at interrupting the abnormal fibrogenic process in this disease.

Endothelial cell apoptosis is a primary pathogenetic event underlying skin lesions in avian and human scleroderma

The mechanism that may cause degenerative fibrotic skin lesions was studied in situ using skin biopsies from patients with systemic sclerosis (SSc), localized scleroderma, or keloids, and at the initial disease stage in the University of California at Davis (UCD) lines 200/206 chickens, which develop a hereditary systemic connective tissue disease resembling human SSc and permit study of disease stages not accessible in humans. Frozen skin sections were analyzed simultaneously for apoptosis by terminal deoxynucleotidyl transferase-mediated FITC-dUTP nick end labeling and indirect immunofluorescence staining of cell markers with tetramethylrhodamine isothiocyanate conjugates. The results showed that endothelial cells are clearly the first cells to undergo apoptosis in the skin of UCD-200/206 chickens, a process that seems to be induced by anti-endothelial cell antibodies. In human fibrotic skin diseases, apoptotic endothelial cells could only be detected in early inflammatory disease stages of SSc and localized scleroderma.

Cultured fibroblasts in avian scleroderma, an autoimmune fibrotic disease, display an activated phenotype

University of California, Davis, line 200 and 206 chickens spontaneously develop an autoimmune syndrome that has many features analogous to human scleroderma, including dermal fibrosis, antinuclear antibodies and antibodies to type II collagen. These birds also have thymic subcapsular epithelial defects and an abnormality in T cell calcium influx and proliferation in response to both T cell receptor-dependent and -independent activators. To determine whether fibroblast activation is a contributing factor to development of skin fibrosis in line 200/206 chickens, as it is in human scleroderma, we studied the collagen, non-collagenous protein and glycosaminoglycan (GAG) production of 34 separate fibroblast lines derived from the normal and fibrotic skin of line 200 and 206 chickens and from the skin of control chicken lines 058 and 254. The mean +/- SEM 24-h incorporation of 3H-proline or 3H-glucosamine into extracellular collagen, non-collagenous protein or GAG by first passage fibroblast lines derived from the fibrotic skin of diseased birds was 1,526 +/- 136, 859 +/- 82 and 25.7 +/- 1.3 dpm/10(3) cells, respectively, while fibroblast lines derived from the skin of control birds produced only 341 +/- 36, 343 +/- 42 and 15.2 +/- 1.4 dpm/10(3) cells. Similar differences in results were recorded for cell-associated production, and when collagen and non-collagenous protein production were assessed using non-radioactive electrophoretic methods. The activated phenotype of the fibroblast lines derived from the fibrotic skin of diseased birds persisted through 10 cell doublings in tissue culture. However, the ratio of type I:III collagen and the profile of GAG types produced were similar in all fibroblast lines studied. These results suggest that fibroblast activation is responsible for the skin fibrosis observed in this avian model of scleroderma.

Avian scleroderma: evidence for qualitative and quantitative T cell defects

T cell activation is dependent upon calcium influx and protein kinase C activation, with subsequent lymphocyte proliferation dependent upon IL-2. Abnormalities in T cell proliferation, including abnormal calcium influx and defective protein kinase C activation, have been identified in aged mice and humans and many autoimmune diseases including diabetes, lupus and scleroderma. Since UCD line 200 chickens, which spontaneously develop a scleroderma-like disease, have both thymic defects and a diminished peripheral blood lymphocyte response to IL-2, we have further investigated T cell function in these birds. Interestingly, line 200 T cells respond poorly in vitro to a variety of diversely acting T cell mitogens including concanavalin A, phytohemagglutinin and anti-chicken CD3 monoclonal antibody. Moreover, they do not respond well even to phorbol myristate acetate in conjunction with ionomycin. Addition of exogenous IL-2-containing supernatant concurrently with mitogenic stimulation also had no significant effect. Analysis of intracellular free calcium demonstrated that the lymphocytes from diseased birds had a reduced influx of calcium (or release for intracellular stores) following stimulation. These data clearly reflect a unique defect in T cell activation associated with avian scleroderma. Analysis of chicken CD3, CD4 and CD8 expression revealed a 39% decrease in peripheral blood CD4+ cells in scleroderma birds, although this decrease was not sufficient to explain the 80-90% decrease observed in proliferation assays and calcium influx. Our data support the hypothesis that avian scleroderma is mediated via abnormal function of lymphocyte co-stimulatory molecules or intracellular calcium regulators.

Expression and function of surface antigens on scleroderma fibroblasts

Dermal fibroblasts from patients with systemic sclerosis (SSc) bound a much greater number of T lymphocytes than did normal dermal fibroblasts. Monoclonal antibodies (MAb) against classes I and II antigens of the major histocompatibility complex (MHC) and their receptors, CD8 and CD4, had no effect on T cell interaction with SSc and normal cells, while MAb against lymphocyte function-associated antigen type 3 (LFA-3) and CD2 both strongly inhibited lymphocyte attachment. MAb against intercellular adhesion molecule type 1 (ICAM-1) and LFA-1 also prevented binding of T lymphocytes, but had a more marked effect on adhesion to SSc fibroblasts than to normal fibroblasts; they also completely abolished the increased binding to fibroblasts treated with interleukin-1 alpha, tumor necrosis factor alpha, and interferon-gamma. No difference was found in the proportion of normal and SSc fibroblasts that expressed MHC classes I and II and LFA-3, but more SSc cells expressed ICAM-1, and at a higher level, than did normal fibroblasts. These results show that cultured SSc cells have elevated binding to T lymphocytes, which possibly results from expansion of a subset of fibroblasts that produces high levels of ICAM-1.

Phenotypic analysis of skin infiltrates in comparison with peripheral blood lymphocytes, spleen cells and thymocytes in early avian scleroderma

University of California at Davis line 200 (UCD-200) chickens develop a hereditary connective tissue disease characterized by severe lymphocytic infiltration, vascular occlusion and fibrosis of skin and internal organs. To identify cellular immunological abnormalities in the acute inflammatory disease stage of this animal model for progressive systemic sclerosis (PSS) we investigated the phenotypic characteristics and function of peripheral blood lymphocytes (PBL), spleen cells and thymocytes in comparison with skin infiltrating cells. Immunofluorescence and immunohistochemical analysis using monoclonal antibodies revealed the overwhelming majority of skin infiltrating mononuclear cells in the deeper dermis and subcutaneous tissue to be T cell receptor alpha/beta (TcR2)+/CD3+/CD4+/class II+ cells, a small portion (5-10%) of which were interleukin 2 (IL-2) receptor positive. In contrast, the inflammatory infiltrate in perivascular areas of the papillary dermis was constituted of mainly TcR gamma/delta (TcR1)+/class II- lymphocytes. Only few B cells (T/B cell ratio greater than 5) were detected. These diseased chickens showed significantly reduced percentages and numbers of circulating peripheral T cells exhibiting TcR1, TcR2, CD3, CD4 or IL-2-receptor, probably owing to an increased influx into lymphoid organs and affected tissues. In contrast to healthy chickens, the thymi of UCD-200 animals revealed fewer cells expressing TcR1, TcR2 and class II antigen, suggesting an altered intrathymic maturation of the T cell lineage. Functional in vitro studies showed a significantly decreased T cell mitogen-induced proliferation rate associated with a decreased capacity to produce IL-2 and to express IL-2 receptors. In contrast to the deficient in vitro IL-2 production the sera of UCD-200 chickens contained significant levels of IL-2 bioactivity. The alteration of T lymphocyte physiology in UCD-200 chickens adds, at least in part, to the parallels between this animal model and its human counterpart. These data confirm our hypothesis that the PSS-like disease of UCD-200 chickens includes a numeric and/or functional alteration of peripheral T cell subsets, especially of TcR1 positive cells, in contrast to the pronounced accumulation in the afflicted tissues.

Selective abnormalities in the thymic microenvironment associated with avian scleroderma, an inherited fibrotic disease of L200 chickens

As a prelude to deciphering the mechanisms of intrathymic T-cell maturation we produced a panel of 18 monoclonal antibodies (mAbs) against chicken thymic stromal elements. Eleven of these detected epithelial cells. They were: pan-epithelial; subcapsule and peri-vascular (pan type 1 epithelium); subcapsular, perivascular and medulla; medulla; or cortex. Of particular interest were the sub-specificities within these regions, especially the subcapsular region. Four mAbs stained both epithelial and non-epithelial cells in discrete regions. In addition, three mAbs recognized only non-epithelial cells. One identified macrophages scattered throughout the thymus, another the connective tissue and another the medullary vascular endothelium. These reagents have provided an extensive profile of the thymic stromal architecture and revealed that these cells are equally as complex as the T cells whose differentiation they induce and regulate. While the mAbs provide a valuable means for studying the mechanisms of normal thymopoiesis, their clinical significance is unknown. UCD line 200 chickens develop an autoimmune disease manifest by dermal and internal organ fibrosis, T cell infiltrates of skin and other affected organs and production of multiple autoantibodies. We have used our panel of mAbs to evaluate the thymic microenvironment in these autoimmunity-prone chickens. A comparative analysis with control chickens revealed striking deficiencies in the L200 subcapsular regions coupled with excessive expression of MHC class II antigens, particularly in the cortex. We hypothesize that these abnormalities induce altered T-cell differentiation, thereby predisposing the L200 chickens to autoimmune disease.

Ontogeny of T cell development in avian scleroderma

UCD line 200 chickens develop an inherited fibrotic disease associated with the production of antinuclear antibodies, antibodies to type II collagen, and early skin lesions characterized by intense T lymphocyte infiltrates. In the present study we have investigated the hypothesis that developmental abnormalities in T lymphocyte differentiation predispose the line 200 chickens to autoimmune disease. The status of the thymic microenvironment in these birds during ontogeny was studied with an extensive panel of monoclonal antibodies (mAbs) reactive with distinct stromal cell subsets including MHC determinants. In addition, their T-cell graft-versus-host reactivity and responses to mitogenic stimulation and interleukin (IL)-2 were also analyzed. Line 200 chickens have profound defects in thymic structure with a virtual complete absence of antigens specific for type I epithelium which lines the thymic subcapsular and perivascular regions. There are excessive levels of MHC class II positive cells, particularly in the cortex, and B cells/subset macrophages identified by mAb MUI 36. These defects are found from the late embryonic period, long before clinical disease is manifest. Furthermore, by FACS analysis, line 200 thymocytes have a major increase in IL-2 receptor density. In addition, line 200 chicken peripheral blood lymphocytes (PBL) respond poorly to mitogenic agents and have a reduced response to IL-2. Finally, it is important to note that line 200 PBL produce a normal graft-versus-host reaction. We propose that these abnormalities in T-cell differentiation are selective, not global, and may be reflective of a defect in thymic education resulting in an inappropriate response to self-antigens.

Genetic control of avian scleroderma

The inheritance of avian scleroderma, a fibrotic autoimmune disease of chickens resembling human scleroderma, was investigated. Comb inflammations and lesions were used to determine the state of disease of 4-week-old chickens. All line 200 males and 60% of female line 200 chicks showed abnormalities. Crosses (F1) between line 200 and eight partially inbred lines of chickens maintained at the University of California at Davis were all normal. Backcrosses of F1 cocks to line 200 hens showed a higher incidence of scleroderma in males than in females for all lines. The incidence of affected birds varied between backcrosses from a low of 42% for backcross line 217 males derived from a New Hampshire line, to 88% for males of backcross line 213 derived from a partially inbred Leghorn line, demonstrating the presence of genes modifying the penetrance of presumed major genes causing the disease. Backcross genotypes segregating for haplotypes of the major histocompatibility complex (MHC) derived from inbred lines showed consistently lower penetrance of scleroderma than homozygotes carrying the line 200 haplotype. Thus B3Bs (lines 211 and 215), B14Bs (line 217), and B15Bs (lines 212, 213, 216, and 218) all had fewer affected individuals than BsBs homozygotes from the same families.