Autoantibodies in systemic sclerosis and fibrosing syndromes: clinical indications and relevance

Endothelin axis polymorphisms in patients with scleroderma

OBJECTIVE

To evaluate the distribution of polymorphisms in the endothelin 1 (EDN1), endothelin receptor A (EDNRA) and endothelin receptor B (EDNRB) genes in systemic sclerosis (SSc; scleroderma) and SSc subsets.

METHODS

Two hundred five patients with SSc and 255 healthy controls were screened for polymorphisms in EDN1, EDNRA, and EDNRB, using sequence-specific primer-polymerase chain reaction. The polymorphisms studied were at the following positions: for EDN1, -1370 (T-1370G) of the promoter, +138 of exon 1 (+138 A/-), +85 of exon 3 (E106E), and +23 of exon 5 (K198N); for EDNRA, -231 of exon 1 (G-231A), and +69(H323H) and +105 (E335E) of exon 6; for EDNRB, +2841 of exon 2 (EDNRB-3), -2547 of exon 3 (EDNRB-2), and -2446 of exon 3 (EDNRB-1).

RESULTS

No significant differences between the SSc group as a whole and control subjects were observed for any of the investigated polymorphisms in EDN1, EDNRA, and EDNRB. However, compared with patients with limited cutaneous SSc, patients with diffuse skin involvement had an increased frequency of allele carriage of EDNRB-1A (76.8% versus 54.4%; P = 0.002), EDNRB-2A (79.7% versus 60.2%; P = 0.006), and EDNRB-3G (79.7% versus 56.6%; P = 0.001). Significantly increased carriage frequencies for EDNRA alleles H323H/C and E335E/A were observed in SSc patients with anti-RNA polymerase (anti-RNAP) antibodies, compared with both anti-RNAP-negative SSc patients (P < 0.05) and control subjects (P < 0.005).

CONCLUSION

The finding of associations between endothelin receptors A and B and distinct clinical and immunologic SSc subsets supports the role of endothelin and its receptors in the pathogenesis of SSc. However, these findings and their functional significance need to be confirmed and investigated in future studies.

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.

Scleroderma: from cell and molecular mechanisms to disease models

Scleroderma [also known as systemic sclerosis (SSc)] is a complex autoimmune disease characterised by pathological remodelling of connective tissues. Although the earliest and most frequent manifestations include blood vessel and immunological abnormalities, the systemic and progressive pathology suggests that fundamental interactions between microvascular damage and inflammation are mechanistically linked to obliterative tissue fibrosis. This review will focus on how model systems have provided clues to these relationships and will discuss new data from the study of novel animal disease models. These reveal how vascular damage and leukocyte accumulation generate the molecular cues that control the profiles of soluble mediators, which regulate the aberrant behaviour of mesenchymal cells within connective tissues, and how the dysregulated expression of these components and their differentiation contribute to the persistent fibrogenic response.

Demonstration of Autoimmunity in the Tight Skin-2 Mouse: A Model for Scleroderma

The tight skin-2 (Tsk2/+) mouse has been proposed as an animal model of systemic sclerosis (SSc) because this animal exhibits increased collagen synthesis and accumulation in the dermis. The Tsk2/+ mouse also has been reported to have a mononuclear cell infiltrate in the dermis; however, to date no evidence of autoimmunity has been described in this animal model. We report here that Tsk2/+ mice harbor numerous autoantibodies in their plasma including some, which are similar to those, present in SSc patients. Immunofluorescence with HEp-2 cells revealed the presence of anti-nuclear Abs (ANAs) in the plasma of 92% of the Tsk2/+ mice. In contrast, <5% of cage-mated CAST/ei mice had a positive ANA and none of the C3H/HeJ age-matched controls were positive. Homogenous, speckled, rim, nucleolar, centromere as well as combinations of these patterns were observed. The proportion of Tsk2/+ animals with a positive ANA increased slightly with age. ELISAs showed that 93% of the Tsk2/+ animals were positive for anti-Scl70, 82% for anti-centromere, 5% for anti-RNP/Sm, and none were positive for anti-RNA-polymerase II Abs. Indirect immunofluorescence with Crithidia luciliae and ELISA for anti-dsDNA Abs showed that 76% of Tsk2/+ mice were positive for this autoantibody. The high frequency of anti-Scl70 and anti-centromere autoantibodies indicates that Tsk2/+ mice display some humoral immune alterations which are similar to those found in patients with SSc. However, the Tsk2/+ mice also develop autoantibodies to dsDNA and a majority of the mice develop multiple autoantibody specificities (anti-Scl70, anti-CENP-B, and anti-dsDNA) indicating that the mouse may be a useful model to study autoimmunity in a wider spectrum of connective tissue diseases.

Diagnostic Tests for Rheumatic Disease: Clinical Utility Revisited

Establishing a diagnosis of systemic rheumatic disease requires an integration of a patient's symptoms, physical examination findings, and the results of diagnostic testing. There is often a temptation by clinicians to rely heavily on objective measures such as the presence or absence of an autoantibody. Medical textbooks and the medical literature may overestimate the diagnostic utility of many commonly ordered tests for rheumatic disease because the tests are usually analyzed among patients with established rheumatic disease rather than among patients with an uncertain cause of symptoms as is common in practice. Few diagnostic tests are highly sensitive, though the antinuclear antibody in systemic lupus erythematosus (SLE) and the erythrocyte sedimentation rate in temporal arteritis are notable exceptions. Conversely, few diagnostic tests are highly specific; anti-proteinase-3 and antimyeloperoxidase antibodies (types of antineutrophilic cytoplasmic antibodies) among patients with Wegener granulomatosis (and related vasculitides) and anti-double-stranded and anti-Smith antibodies among patients with SLE may be particularly helpful in the proper clinical settings due to their high specificity. Anticitrullinated cyclic protein (anti-CCP), a newly described autoantibody that may be highly specific for rheumatoid arthritis, requires additional study as its utility in clinical practice is uncertain.