A new serologic marker in ankylosing spondylitis

Diagnosing early ankylosing spondylitis

Diagnosis of ankylosing spondylitis is still delayed by many years. Several efforts have been made in the past few years to shorten this delay. A new set of criteria for inflammatory back pain has performed better than previous sets. MRI has evolved to become the standard imaging modality for the detection of sacroiliitis during early disease, and it clearly outperforms quantitative scintigraphy, which was the standard screening test for many years. Promising new developments such as whole body MRI and ultrasound (sonography) for the detection of enthesitis or sacroiliitis deserve further evaluation. Serum antibodies directed against a 28-kD Drosophila antigen may provide additional diagnostic information. A recently proposed diagnostic algorithm in patients with suspected early ankylosing spondylitis may help physicians confidently diagnose patients before definite radiographic sacroiliitis is detectable. Finally, referral strategies for patients seen by primary care physicians seem to work well and are currently under further valuation.

High positive predictive value of specific antibodies cross-reacting with a 28-kDa Drosophila antigen for diagnosis of ankylosing spondylitis

OBJECTIVES

Diagnosis of ankylosing spondylitis (AS) can be difficult, and a specific laboratory test has not yet been introduced as a routine diagnostic tool. Our aim was to evaluate the diagnostic value of antibodies specifically binding to a recombinant 28-kDa antigen for the diagnosis of AS.

METHODS

Blinded sera were tested for antibodies binding to the procaryotically expressed 28-kDa protein using an enzyme-linked immunosorbent assay (ELISA). This purified 28-kDa protein is produced by a specific clone from an embryonic Drosophila hydei Xgtl I c-DNA library and is bound by human antibodies cross-reacting with both a 36-kDa protein of chromosomes from Drosophila melanogaster and a 69-Da HeLa S3 protein potentially involved in signal transduction pathways.

RESULTS

Serum concentrations of antibodies cross-reacting with this specific antigen were increased in 371 patients with AS compared with 37 healthy controls (39.5 vs 22.6 U/ml; P = 0.004). The positive predictive values of this ELISA test for AS were between 95.1% (95% confidence interval 90.6-97.9%) for a cut-off level of 50 U/ml and 97.4% (92.7-99.5%) for a cut-off level of 75 U/ml, and the sensitivities were between 42.1% (37.0-47.3%) for a cut-off level of 50 U/ml and 30.7% (26.1-35.7%) for a cut-off level of 75 U/ml.

CONCLUSIONS

Serum ELISA tests for antibodies cross-reacting with the 28-kDa antigen show a high positive predictive value for AS of more than 95%.

Anti-heat-shock protein antibodies in rheumatic and autoimmune diseases

The heat-shock proteins (hsp) are a family of molecules that have different molecular weights and are thought to operate as scavengers that trap abnormal proteins and protect the stressed cells. These molecules, which have been conserved during evolution, have highly identical stretches of their amino acid sequence in bacteria as well as in humans. Experiments show that arthritis patients manifest T-cell responses to the hsp-65-kD molecule, as do rats with adjuvant arthritis. The B cell response to hsp has not been extensively studied. Autoantibodies against hsp 65, 70, and 90 have been detected in various rheumatic and autoimmune disorders such as rheumatoid arthritis, ankylosing spondylitis, systemic lupus erythematosus, and inflammatory bowel diseases. The frequency of these antibodies varies among studies and is mainly dependent on the methods of detection. Studies on sensitivity and specificity of these antibodies do not exist; therefore, their significance should be interpreted cautiously.

The 93D (hsr-omega) locus of Drosophila: non-coding gene with house-keeping functions

The 93D, or hsr-omega (heat-shock RNA-omega), locus of Drosophila melanogaster and other species of Drosophila, besides being induced as a member of the heat shock gene family, is also selectively and singularly inducible by a variety of agents, notably benzamide, colchicine and vitamin B6 (in species other than D. melanogaster). The genomic structure of this locus is highly conserved in all species, although the primary base sequence has diverged rapidly between species. Three transcripts (two nuclear and one cytoplasmic) are produced by this locus but none of them has any significant protein coding capacity. The profile of the three transcripts varies in a developmental and inducer-specific manner. This locus is developmentally active in nearly all cell types and is essential for viability of flies. Its induction during heat shock is independent of the other members of the heat shock gene family. The other selective inducers act on this locus through separate response elements. hsr-omega activity has a characteristic effect on transcription/turnover of the heat shock induced hsp70 and the alpha-beta transcripts in D. melanogaster. It appears that the hsr-omega locus has important house-keeping functions in transport and turnover of some transcripts and in monitoring the 'health' of the translational machinery of the cell.

Are heat shock proteins involved in autoimmunity?

Heat shock proteins (HSPs) have been postulated to be critical antigens in both autoimmune disease and experimental models of autoimmunity. This postulate has been largely based on the remarkable conservation of aminoacid sequence between human and bacterial HSPs, so that it has been argued that immune responses initially directed against the HSP of an infectious agent, would have the potential to initiate or maintain autoimmune disease. This would apply especially to T cell recognition of HSPs, since the T cell focuses on short peptide epitopes within a protein antigen rather than on the antigen's secondary structure. This article critically evaluates the available experimental evidence relating to this hypothesis: although research has clearly highlighted the central role of HSPs in the cellular immune response to pathogenic organisms and has shown the potential for T cell responses directed against self HSPs, a role for self HSPs as major target antigens in autoimmune disease has yet to be firmly established.

Ankylosing spondylitis: an autoimmune disease?

Identification of several autoantibodies in serum samples from patients with ankylosing spondylitis or suspected ankylosing spondylitis is reported. Five antibodies associated with ankylosing spondylitis were identified by applying cytoimmunofluorescence and immunoblotting techniques to antigen pools from insect tissue. At least one of these antibodies was found in 82% of serum samples from patients with ankylosing spondylitis. A 36 kD drosophila antigen, which showed the most common and most dominant reaction, was further purified and isolated. Thirty two (34%) of the serum samples from 95 patients with definite ankylosing spondylitis and 12 (28%) of the serum samples from 43 patients with suspected ankylosing spondylitis reacted with this antigen. Antibodies purified from the 36 kD antigen reacted specifically with a 69 kD antigen present in separations of total protein preparations from human lymphocytes and HeLa cells. The 36 kD antibody was not found in 29 patients with rheumatoid arthritis nor in 38 apparently healthy controls. The prevalence of the 36 kD antibody was comparable in HLA-B27 positive and negative patients. In addition, the same immunoreaction was found in patients with so called 'seronegative' spondylarthropathies, particularly of the ankylosing spondylitis-type, suggesting that this antibody is specific for ankylosing spondylitis or other 'seronegative' spondylarthropathies with the typical clinical and radiological changes of ankylosing spondylitis.

Stress proteins, autoimmunity, and autoimmune disease

At birth, the immune system is biased toward recognition of microbial antigens in order to protect the host from infection. Recent data suggest that an important initial line of defense in this regard involves autologous stress proteins, especially conserved peptides of hsp60, which are presented to T cells bearing gamma delta receptors by relatively nonpolymorphic class lb molecules. Natural antibodies may represent a parallel B cell mechanism. Through an evolving process of "physiological" autoreactivity and selection by immunodominant stress proteins common to all prokaryotes, B and T cell repertoires expand during life to meet the continuing challenge of infection. Because stress proteins of bacteria are homologous with stress proteins of the host, there exists in genetically susceptible individuals a constant risk of autoimmune disease due to failure of mechanisms for self-nonself discrimination. That stress proteins actually play a role in autoimmune processes is supported by a growing body of evidence which, collectively, suggests that autoreactivity in chronic inflammatory arthritis involves, at least initially, gamma delta cells which recognize epitopes of the stress protein hsp60. Alternate mechanisms for T cell stimulation by stress proteins undoubtedly also exist, e.g., molecular mimicry of the DR beta third hypervariable region susceptibility locus for rheumatoid arthritis by a DnaJ stress protein epitope in gram-negative bacteria. While there still is confusion with respect to the most relevant stress protein epitopes, a central role for stress proteins in the etiology of arthritis appears likely. Furthermore, insight derived from the work thus far in adjuvant-induced arthritis already is stimulating analyses of related phenomena in autoimmune diseases other than those involving joints. Only limited data are available in the area of humoral autoimmunity to stress proteins. Autoantibodies to a number of stress proteins have been identified in SLE and rheumatoid arthritis, but their pathogenetic significance remains to be established. Nevertheless, the capacity of certain stress proteins to bind to multiple proteins in the nucleus and cytoplasm both physiologically and during stress or injury to cells, suggests that stress proteins may be important elements in the "immunogenic particle" concept of the origin of antinuclear and other autoantibodies. In short, this fascinating group of proteins, so mysterious only a few years ago, has impelled truly extraordinary new lines of investigation into the nature of autoimmunity and autoimmune disease.

Heat shock proteins and the immune response

Heat shock proteins (HSPs) or stress proteins are produced by prokaryotic and eukaryotic cells in response to a variety of insults. After this original definition, it has become increasingly clear that HSPs can modify the function and destiny of other proteins and thus play an important role in numerous physiological processes. The heat shock response is one of the most universal reactions known and HSPs are among the most conserved molecules in phylogeny. Here Stefan H.E. Kaufmann discusses the role of HSPs in immunity with respect to both their function and their antigenicity.

Parasite heat-shock proteins

Many parasites, including most of those of medical or veterinary importance, experience a major increase in ambient temperature at some stage during their life cycle. This occurs when a cyst or free-living larval form is ingested by a warm-blooded host, when a poikilotherm-infecting parasite is transmitted to a homeotherm, or when a transiently free-living invasive larva penetrates the skin of a mammal. This sudden change in temperature could be expected to stress the intruder, as it should dramatically alter rates of metabolic reactions and of denaturation of proteins. This would especially affect the function of near-equilibrium, regulatory, and membrane-bound enzymes (changes in temperature affect membrane fluidity). In this article George Newport, Janice Culpepper and Nina Agabian consider how parasites cope with this problem, emphasizing the possible role of heat-shock proteins (HSPs), how the expression of these molecules is regulate, and how HSPs interact with the host immune system.

Attempts towards a serological diagnosis of ankylosing spondylitis

Polytene chromosomes of salivary glands as well as nuclear proteins from Kc-cells of Drosophila melanogaster have been used as substrate to identify and evaluate the diagnostic value of crossreacting antibodies present in sera of AS patients. The diagnostic significance of the recently described anti-93D antibody (Lakomek et al., 1984) was confirmed by screening sera of patients with definite or suspected AS using cytoimmunofluorescence on the polytene chromosomes. In addition, four new antibodies could be identified in AS sera by immunoblotting. Simultaneous detection of these antibodies supports the diagnosis of AS and is most useful in diagnosis of early stages of this disease.

Undifferentiated arthritis and spondylarthropathy as a major problem of diagnosis and classification

Epidemiologically-based studies have shown that 20-50% of all cases of early arthritis cannot be classified. More recent data came from experiences with an outpatient clinic especially for early arthritis. Of 149 patients with inflammatory rheumatic disease, 39 (26%) were diagnosed as undifferentiated arthritis and 22 (15%) had a probable diagnosis. Therefore, despite diagnostic progress in recent years, only half of all cases can be diagnosed definitely. Follow-up studies of patients with HLA-B27 positive arthritis and undifferentiated spondylarthropathy show the difficulties of early diagnosis and the heterogeneity of disease course and prognosis. Early diagnostic criteria combining the result of the HLA-B27 test with history, symptoms, erythrocyte sedimentation rate and radiological spinal signs can predict or exclude the development of ankylosing spondylitis (AS) at an early stage of the disease in three-quarters of patients, but the diagnosis of AS should not be excluded before 5 to 10 years' observation.