Animal models in scleroderma.

Scleroderma or systemic sclerosis is an insidious connective tissue disease with no known cure. A hallmark feature of scleroderma is the excess synthesis and deposition of collagen resulting in a fibrotic state. In scleroderma, fibrosis is not confined only to the skin but impacts internal organs as well. In an effort to better understand the pathophysiology of this disease, researchers have developed a variety of animal models that display features of the human condition. This paper focuses on mouse models of scleroderma and summarizes work conducted with these experimental paradigms that is focused on understanding the cellular and molecular events associated with the onset and maintenance of fibrosis.

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.

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.

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

University of California, Davis (UCD) line 200 chickens spontaneously develop a progressive fibrotic syndrome with features similar to those observed in human autoimmune connective tissue diseases, including fibrosis, vascular occlusion, and lymphocytic infiltration of the comb, skin, digits, and viscera. Beginning at 2 weeks post hatch, line 200 chickens develop intense lymphocytic infiltration of the comb and dorsal neck skin. To further characterize the nature of these cellular infiltrates, weekly serial skin biopsy specimens from line 200 and control birds were examined using hematoxylin and eosin staining and indirect immunofluorescence with a library of mouse anti-chicken monoclonal antibodies specific for lymphocyte markers. In situ staining performed on serial skin sections revealed the presence of large groups of T cells beginning at 2 weeks of age. Further characterization of these infiltrates demonstrated the presence of both T helper and T cytotoxic/suppressor cells with a mean +/- SD T4:T8 ratio of 1.44 +/- 0.29 by 4 weeks of age. As the lesions progressed, the infiltrates also contained distinct groups of B cells as characterized by MUI 36. In addition, the lesions were strongly positive for B-L (Ia) antigen, which was noted on B cells, monocytes/macrophages, activated T cells, and fibroblasts. The skin sections were negative for 2 different macrophage monoclonal antibodies at all time-points. Upon extraction from affected skin, 42.0 +/- 13.06% (mean +/- SD) of these cells were positive for B-L, 35.10 +/- 6.51% were T cells, and 31.25 +/- 3.14% were recognized by MUI 36. Although positive staining for IgG was not found in these extracted cells, 7% of the isolated cells were positive for surface IgM.

Serial observations and definition of mononuclear cell infiltrates in avian scleroderma, an inherited fibrotic disease of chickens.

University of California, Davis (UCD) line 200 chickens develop an inherited connective tissue disease which includes fibrosis, vascular occlusion, and lymphocytic infiltration of skin, comb, and viscera. To further identify the nature of these features, tissue from both affected and control chickens, aged 7 days to 12 months, was serially examined using hematoxylin-eosin and Masson's trichrome stain. Mononuclear cell accumulations in skin were simultaneously characterized using mouse anti-chicken T and B cell specific monoclonal antibodies in a solid-phase immunoperoxidase assay; the same cells were also examined by direct immunofluorescence with fluoresceinated anti-chicken IgM and IgG, and stained for esterase and acid phosphatase. At 6 weeks of age, the majority of line 200 chicks manifested dermal fibrosis, cellular infiltrates, and vessel anomalies. In contrast, visceral involvement did not reach maximum incidence until 5 months of age with involvement of small intestine (60%), lungs (60%), and kidneys (65%), and not until 1 year for esophagus (64%), heart (30%), and testes (66%). Moreover, and of particular interest, was the threefold increment of full-thickness skin biopsies in line 200 birds. The cellular infiltrates in skin, found in 100% of affected line 200 chickens, were positive for B1, a mature B cell marker found on peripheral blood and bursal B cells; the majority of these same cells were found to bear surface IgM but not IgG. These data suggest that this syndrome may result from an alteration in collagen metabolism associated with a mature subpopulation of B lymphocytes.

Diversity of autoantibodies in avian scleroderma. An inherited fibrotic disease of White Leghorn chickens.

University of California, Davis line 200 White Leghorn chickens develop an inherited progressive fibrotic disease that includes the appearance of antinuclear antibodies (ANA). To further characterize these ANA, serial aged line 200 birds were studied. Greater than 50% of line 200 birds develop antinuclear and anticytoplasmic antibodies; fluorescent staining patterns included cytoplasmic spider web, most prevalent at 1 mo of age, and fine speckled patterns, characteristic of chickens 6 mo and older. By enzyme-linked immunosorbent assay, 40.4% of line 200 birds were found to have antibodies to single-stranded DNA (ssDNA). In contrast, antibodies to histones, RNA, or poly A . poly U were not detected. Precipitating antibodies to saline extracts from chicken liver were noted in 33.3% of line 200 birds. Saline extracts from turkey, pheasant, and partridge liver but not rat, rabbit, or mouse tissues were also positive in immunodiffusion testing with these line 200 birds. The antigenicity of chicken liver extracts was sensitive to pronase, protease K. and pH variations greater than 10 and less than 5; however, they were resistant to trypsin. DNase. RNase, and incubation at 37 degrees C and 56 degrees C for 1 h. Cell fractionation in conjunction with column chromatographic techniques revealed that several protein antigens with apparent molecular weights in the range of 62,000-290,000 were present in cytoplasm but not in isolated nuclei. Line 200 sera were not reactive against nuclear ribonucleoprotein, Sm, Scl-70, or SS-B/La antigens. Thus, line 200 chickens develop antinuclear and anticytoplasmic antibodies at an early age, which recognize a unique group of protein antigenic determinants found only in avian species. Moreover, and of particular interest, the presence of autoantibodies to saline-extractable antigens correlated with positive ANA, antibodies in ssDNA, and to the clinical expression of disease.

Characterization of a spontaneous disease of white leghorn chickens resembling progressive systemic sclerosis (scleroderma).

University of California, Davis (UCD) line 200 White Leghorn Chickens spontaneously develop a syndrome that has many analogous features to human progressive systemic sclerosis. This syndrome is characterized by progressive involution of comb, dermal fibrosis, and distal polyarthritis. These three features occur within 6 wk after hatching, and are accompanied by a 40% mortality as a result of vaso-occlusive disease, with development of secondary infection of peripheral gangrenous lesions. Birds that survive greater than 2 mo after hatching progressively develop fibrosis of the esophagous and mononuclear infiltration of heart and kidney, with prominent occlusion of small and medium sized blood vessels. In addition, line 200 chickens develop rheumatoid factors, antinuclear antibodies, and antibodies to collagen, but do not have antibodies to thymocytes, DNA, or extractable nuclear antigens. Moreover, antinuclear antibodies when studied using HEp-2 cells as substrate demonstrate predominantly a speckled pattern. This syndrome of line 200 chickens is not detectable in F1 crosses to several UCD inbred lines. F1 X parental line BC1 backcrosses have an approximately 50% incidence of disease, suggesting that this syndrome is inherited as autosomal recessive. However, only 4% of F2 generation birds show abnormal symptoms, suggesting the presence of modifying genes. There is no appearance of IgG deposition, as determined by immunofluorescence, in either skin, blood vessels, esophagus, or heart. However, approximately 20% of chickens have a glomerulonephritis; this feature appears to be a terminal event and does not appear clinically significant. Although this syndrome of line 200 chickens has several features that are in sharp distinction to human scleroderma, the presence of common immunologic and pathologic denominators suggest that this spontaneous disease may be an appropriate model to develop a better understanding of autoimmune connective tissue diseases.