Diagnostic classification of spondylarthropathy and rheumatoid arthritis by synovial histopathology: a prospective study in 154 consecutive patients

Distinct synovial immunopathologic characteristics of juvenile-onset spondylarthritis and other forms of juvenile idiopathic arthritis

OBJECTIVE

To characterize the synovial immunopathologic features of juvenile-onset spondylarthritis (SpA) in relation to adult SpA and other forms of juvenile idiopathic arthritis (JIA).

METHODS

Synovial biopsy samples were obtained from 10 patients with juvenile-onset SpA, 23 with adult SpA, 19 with rheumatoid arthritis (RA), 8 with juvenile polyarthritis, and 12 with juvenile oligoarthritis. Synovial immunopathologic features were studied by extensive histologic and immunohistochemical analyses.

RESULTS

Synovitis in juvenile SpA was characterized by marked lining layer hyperplasia, clear hypervascularity, and pronounced inflammatory cell infiltration with lymphocytes and macrophages, independent of disease duration or time of sampling. The immunopathologic features of juvenile SpA resembled those of adult SpA in terms of hypervascularity and absence of RA-specific intracellular citrullinated proteins and HLA-DR4/human cartilage glycoprotein 39(263-275) complexes, but differed markedly by a stronger lining layer hyperplasia and lower numbers of CD163+ macrophages. Accordingly, class prediction analysis failed to classify juvenile SpA synovitis in the SpA group. Comparison of juvenile SpA with other JIA subtypes showed a broad overlap, with the exception of slightly lower vascularity in juvenile polyarthritis and higher inflammatory cell infiltration in juvenile oligoarthritis. Unsupervised clustering analysis identified a subgroup of samples characterized by high plasma cell infiltration, which corresponded with active, longstanding JIA, mostly of the oligoarthritis subtype.

CONCLUSION

Despite some similarities with adult SpA, the findings with regard to lining layer hyperplasia and CD163+ macrophage infiltration are indicative of important differences in the synovial immunopathologic features of juvenile-onset SpA. The partial overlap with other JIA subtypes emphasizes the need for further biologic characterization of JIA in order to define pathophysiologic, rather than phenotypic, subgroups.

Diagnostic value of blind synovial biopsy in clinical practice

OBJECTIVE

To assess the diagnostic value of blindly performed synovial biopsies in carefully selected patients with unclassified arthritis.

METHODS

Synovial tissue was obtained blindly under local anaesthesia. The Arthroforce III take-apart 3.5 mm needle and 1.5 mm grasping forceps were used for this purpose.

RESULTS

Four patients with unclassified arthritis could be diagnosed properly based upon examination of synovial tissue of the knee obtained by an easy-to-perform blind biopsy. The arthritis of the four patients was diagnosed as being part of Erdheim-Chester disease, sarcoidosis, multicentric reticulohistiocytosis and arthritis caused by foreign-body material, respectively.

CONCLUSIONS

Analysis of synovial tissue obtained during a blind biopsy procedure has diagnostic potential in carefully selected patients with unclassified arthritis. The common denominator in all the cases presented was a differential diagnosis consisting of a rheumatological disease with characteristic histological features.

Synovial biopsy

In patients with arthritis, synovial tissue is easily accessible for analysis. Blind needle biopsy is a simple and safe procedure. Arthroscopic biopsy is also safe, it allows access to most sites in the joint and it can provide adequate tissue for extensive laboratory investigations, both before and after successful therapy. Synovial tissue analysis has been successfully applied to the study of disease mechanisms and response to treatment. In addition, there may be an indication for diagnostic synovial biopsy in selected cases.

Classification of the spondyloarthropathies

PURPOSE OF REVIEW

The spondyloarthropathies are a group of conditions which share similar clinical features. Classification criteria permit separation of the conditions, allow better targeting of therapies, better measurement of outcomes, and better prognostic information. Early diagnosis remains problematic, but validated criteria for established disease are now emerging.

RECENT FINDINGS

Histopathology and histochemistry are providing a better understanding of the underlying process of inflammatory arthritis in spondyloarthropathy and other inflammatory arthritides. Early disease, however, continues to challenge current criteria. Sophisticated imaging with magnetic resonance imaging is being increasingly used and is proving useful for early diagnosis as well as helping to understand the pathophysiology of disease. Juvenile idiopathic arthritis continues to provide problems and criteria have recently been modified to allow a greater clinical utility and inclusion of more patients. Poststreptococcal reactive arthritis appears to be a heterogeneous clinical entity, with a group looking more like rheumatic fever and a group with spondyloarthropathy traits. It may be that the association is not streptococcal, but is a throat infection. Currently available criteria for psoriatic arthritis have been evaluated in a large cohort. Four of the criteria performed well with high specificity and sensitivity whereas the other two had moderate specificity and low sensitivity. It was shown that rheumatoid factor positivity does not exclude a diagnosis of psoriatic arthritis--the single most important clinical feature of this condition being the presence of psoriasis.

SUMMARY

The spondyloarthropathy classification criteria continue to be an area of development. This is most apparent in juvenile arthritis and psoriatic arthritis. The latter is currently undergoing intense scrutiny to develop classification criteria and outcome measures.

Synovial intracellular citrullinated proteins colocalizing with peptidyl arginine deiminase as pathophysiologically relevant antigenic determinants of rheumatoid arthritis-specific humoral autoimmunity

OBJECTIVE

To address the ongoing debate concerning the specificity of synovial citrullinated proteins for rheumatoid arthritis (RA) and to analyze their pathophysiologic relevance to the induction or perpetuation of the RA-specific anti-citrullinated protein antibodies (ACPAs).

METHODS

Synovium of 19 RA patients and 19 non-RA controls was immunostained for the presence of citrullinated proteins with a mouse monoclonal antibody (F95), for the citrullinating enzyme peptidyl arginine deiminase type 2 (PAD-2), and for the free citrulline-producing enzyme inducible nitric oxide synthase (iNOS). Extending the RA cohort to 61 patients, the findings of anticitrulline staining in synovium were related to serum and synovial fluid ACPA levels, as measured by enzyme-linked immunosorbent assay.

RESULTS

F95 staining indicated the presence of synovial intracellular citrullinated proteins in 53% of RA samples versus 5% of control samples, whereas extracellular staining was not RA specific. Immunoblotting and inhibition experiments confirmed that the antibody recognized citrullinated proteins but not free citrulline. Accordingly, iNOS was equally found in RA and control synovium and in intracellular citrullinated protein-positive and intracellular citrullinated protein-negative samples. In contrast, intracellular citrullinated proteins colocalized with PAD-2, which was found in 59% of RA samples versus 17% of control samples. Independent of local disease activity, the presence of the RA-specific synovial intracellular citrullinated proteins was associated with significantly higher systemic and local ACPA levels and with local ACPA production in the joint.

CONCLUSION

These data confirm the presence of RA-specific intracellular citrullinated proteins in synovium. The link with PAD-2 and local and systemic ACPA levels emphasizes their pathophysiologic relevance for RA-specific humoral autoimmunity.

Involvement of neurotrophins and their receptors in spondyloarthritis synovitis: relation to inflammation and response to treatment

OBJECTIVE

To investigate whether expression of the four members of the neurotrophin (NT) family and their four corresponding receptors is related to synovial inflammation in patients with spondyloarthritis (SpA).

MATERIAL AND METHODS

Synovial fluid (SF) and serum NTs and their receptors were measured by ELISA. Immunohistochemistry was used for synovial tissue biopsy specimens from patients with SpA, rheumatoid arthritis, and osteoarthritis (OA). In SpA synovium, immunoreactivity of the receptors trkA and NGFRp75 was also assessed before and after 12 weeks of treatment with the monoclonal anti-tumour necrosis factor alpha antibody, infliximab.

RESULTS

mRNA transcripts of all NTs and receptors were expressed in the inflamed synovium. At the protein level, brain derived neurotrophic factor and NT-3 were significantly higher in the SF of patients with SpA than in those with OA. In contrast, ELISA of serum samples showed that the highest member in SpA was NT-4. Immunohistochemistry demonstrated that the NT receptors trkA and NGFRp75 were highly expressed in the inflamed synovium of patients with SpA, correlating with vascularity and lymphoid aggregates, respectively. Additionally, immunoreactivity of both receptors was significantly decreased after infliximab treatment.

CONCLUSIONS

NTs and their receptors are expressed in inflamed peripheral joints of patients with SpA. Their expression is not constitutive but related to inflammation and they may be involved in the local disease processes.

Functional haplotypes of PADI4: relevance for rheumatoid arthritis specific synovial intracellular citrullinated proteins and anticitrullinated protein antibodies

BACKGROUND

Haplotypes of PADI4, encoding for a citrullinating enzyme, were associated with rheumatoid arthritis in a Japanese population. It was suggested they were related to the presence of anticitrullinated protein antibodies (ACPA).

OBJECTIVE

To explore the relation between PADI4 haplotypes, the presence of rheumatoid arthritis specific intracellular citrullinated proteins in synovial membrane, and serum ACPA titres.

METHODS

Synovial biopsies and peripheral blood samples were obtained in 59 patients with rheumatoid arthritis. Synovial intracellular citrullinated proteins were detected by immunohistochemistry. Serum ACPA titres were measured by anti-CCP2 ELISA. PADI4 haplotypes were determined by direct sequencing of the four exonic PADI4 single nucleotide polymorphisms.

RESULTS

PADI4 haplotype frequencies and the presence of synovial intracellular citrullinated proteins and ACPA were comparable with previous studies. There was no significant association between PADI4 haplotype 1 or 2 and the presence of synovial intracellular citrullinated proteins, although these proteins were associated with higher serum ACPA. There was no correlation between PADI4 haplotypes and serum ACPA, either by continuous analysis using the titres or by dichotomous analysis using the diagnostic cut off. Further analyses in homozygotes for haplotype 1 or 2 or in heterozygotes (1/2) also failed to show an association between PADI4 polymorphisms and ACPA. This contrasted with the clear association between ACPA levels and HLA-DR shared epitope.

CONCLUSIONS

The link between synovial intracellular citrullinated proteins and ACPA emphasises the role of deimination of synovial proteins in rheumatoid arthritis, but the biological relevance of the PADI4 haplotypes for this autoimmune process is questionable, at least in a European population.

Synovial histopathology of psoriatic arthritis, both oligo- and polyarticular, resembles spondyloarthropathy more than it does rheumatoid arthritis

At present only few biological data are available to indicate whether psoriatic arthritis (PsA) is part of the spondyloarthropathy (SpA) concept, whether it is a separate disease entity or a heterogeneous disease group with oligoarticular/axial forms belonging to SpA and polyarticular forms resembling rheumatoid arthritis (RA). To address this issue with regard to peripheral synovitis, we compared the synovial characteristics of PsA with those of ankylosing spondylitis (AS)/undifferentiated SpA (USpA) and RA, and compared the synovium of oligoarticular versus polyarticular PsA. Synovial biopsies were obtained from patients with RA, nonpsoriatic SpA (AS + USpA), and oligoarticular and polyarticular PsA. The histological analysis included examination(s) of the lining layer thickness, vascularity, cellular infiltration, lymphoid aggregates, plasma cells and neutrophils. Also, we performed immunohistochemical assessments of CD3, CD4, CD8, CD20, CD38, CD138, CD68, CD163, CD83, CD1a, CD146, alphaVbeta3, E-selectin, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, S100A12, intracellular citrullinated proteins and major histocompatibility complex (MHC)-human cartilage (HC) gp39 peptide complexes. Comparing SpA (PsA + AS + USpA) with RA, vascularity, and neutrophil and CD163+ macrophage counts were greater in SpA (P < 0.05), whereas lining layer thickness and the number of CD83+ dendritic cells were greater in RA (P < 0.05). In RA, 44% of samples exhibited positive staining for intracellular citrullinated proteins and 46% for MHC-HC gp39 peptide complexes, whereas no staining for these markers was observed in SpA samples. We excluded influences of disease-modifying antirheumatic drug and/or corticosteroid treatment by conducting systematic analyses of treated and untreated subgroups. Focusing on PsA, no significant differences were observed between PsA and nonpsoriatic SpA. In contrast, vascularity (P < 0.001) and neutrophils were increased in PsA as compared with RA (P = 0.010), whereas staining for intracellular citrullinated proteins and MHC-HC gp39 peptide complexes was exclusively observed in RA (both P = 0.001), indicating that the same discriminating features are found in PsA and other SpA subtypes compared with RA. Exploring synovial histopathology between oligoarticular and polyarticular PsA, no significant differences were noted. Moreover, intracellular citrullinated proteins and MHC-HC gp39 peptide complexes, which are specific markers for RA, were observed in neither oligoarticular nor polyarticular PsA. Taken together, these data indicate that the synovial histopathology of PsA, either oligoarticular or polyarticular, resembles that of other SpA subtypes, whereas both groups can be differentiated from RA on the basis of these same synovial features, suggesting that peripheral synovitis in PsA belongs to the SpA concept.

Infiltration of the synovial membrane with macrophage subsets and polymorphonuclear cells reflects global disease activity in spondyloarthropathy

Considering the relation between synovial inflammation and global disease activity in rheumatoid arthritis (RA) and the distinct but heterogeneous histology of spondyloarthropathy (SpA) synovitis, the present study analyzed whether histopathological features of synovium reflect specific phenotypes and/or global disease activity in SpA. Synovial biopsies obtained from 99 SpA and 86 RA patients with active knee synovitis were analyzed for 15 histological and immunohistochemical markers. Correlations with swollen joint count, serum C-reactive protein concentrations, and erythrocyte sedimentation rate were analyzed using classical and multiparameter statistics. SpA synovitis was characterized by higher vascularity and infiltration with CD163⁺ macrophages and polymorphonuclear leukocytes (PMNs) and by lower values for lining-layer hyperplasia, lymphoid aggregates, CD1a⁺ cells, intracellular citrullinated proteins, and MHC–HC gp39 complexes than RA synovitis. Unsupervised clustering of the SpA samples based on synovial features identified two separate clusters that both contained different SpA subtypes but were significantly differentiated by concentration of C-reactive protein and erythrocyte sedimentation rate. Global disease activity in SpA correlated significantly with lining-layer hyperplasia as well as with inflammatory infiltration with macrophages, especially the CD163⁺ subset, and with PMNs. Accordingly, supervised clustering using these synovial parameters identified a cluster of 20 SpA patients with significantly higher disease activity, and this finding was confirmed in an independent SpA cohort. However, multiparameter models based on synovial histopathology were relatively poor predictors of disease activity in individual patients. In conclusion, these data indicate that inflammatory infiltration of the synovium with CD163⁺ macrophages and PMNs as well as lining-layer hyperplasia reflect global disease activity in SpA, independently of the SpA subtype. These data support a prominent role for innate immune cells in SpA synovitis and warrant further evaluation of synovial histopathology as a surrogate marker in early-phase therapeutic trials in SpA.

Tumor necrosis factor α blockade treatment down-modulates the increased systemic and local expression of toll-like receptor 2 and toll-like receptor 4 in spondylarthropathy

OBJECTIVE

Abnormal host defense against pathogens has been implicated in the pathogenesis of spondylarthropathy (SpA), a disease characterized by abundant synovial infiltration with innate immune cells. Given the role of Toll-like receptors (TLRs) in activation of innate inflammation and the occurrence of TLR-dependent infections after tumor necrosis factor alpha (TNFalpha) blockade treatment, the present study was undertaken to analyze TLRs and their modulation by TNFalpha blockade in SpA.

METHODS

Peripheral blood mononuclear cells (PBMCs) were obtained from SpA and rheumatoid arthritis (RA) patients during infliximab therapy, and from healthy controls. TLR-2 and TLR-4 expression and TNFalpha production upon lipopolysaccharide (LPS) stimulation were analyzed by flow cytometry on different monocyte subsets. Synovial biopsy specimens from 23 SpA patients before and after infliximab or etanercept treatment, from 15 RA patients, and from 18 osteoarthritis (OA) patients were analyzed by immunohistochemistry.

RESULTS

Expression of TLR-4, but not TLR-2, was increased on PBMCs from patients with SpA, whereas both TLRs were increased in RA patients. TLR expression was particularly increased on the CD163+ macrophage subset. Infliximab reduced TLR-2 and TLR-4 expression on monocytes of SpA and RA patients, leading to lower levels than in controls and to impaired TNFalpha production upon LPS stimulation. In inflamed synovium, the expression of both TLRs and of CD163 was significantly higher in patients with SpA than in those with RA or OA. Paralleling the systemic effect, TLRs in synovium were down-regulated following treatment with infliximab as well as etanercept, indicating a class effect of TNFalpha blockers.

CONCLUSION

Inflammation in SpA is characterized by increased TLR-2 and TLR-4 expression, which is sharply reduced by TNFalpha blockade. These findings suggest a potential role of innate immunity-mediated inflammation in SpA and provide an additional clue regarding the mechanism of action as well as the potential side effects of TNFalpha blockade.