Connective Tissue Degeneration: Mechanisms of Palmar Fascia Degeneration (Dupuytren's Disease).

Dupuytren's disease is a connective tissue disorder of the hand causing excessive palmar fascial fibrosis with associated finger contracture and disability. The aetiology of the disease is heterogeneous, with both genetic and environmental components. The connective tissue is abnormally infiltrated by myofibroblasts that deposit collagen and other extracellular matrix proteins. We describe the clinical profile of Dupuytren's disease along with current therapeutic schemes. Recent findings on molecular and cellular parameters that are dysregulated in Dupuytren's disease, which may contribute to the onset of the disease, and the role of resident inflammation promoting fibrosis, are highlighted. We review recent literature focusing on non-myofibroblast cell types (stem cell-like cells), their pro-inflammatory and pro-fibrotic role that may account for abnormal wound healing response.

Characterization of synovial mast cells in knee osteoarthritis: association with clinical parameters.

OBJECTIVE: To investigate the presence of mast cells in the osteoarthritic (OA) synovium and their association with clinical parameters in comparison with rheumatoid arthritis (RA) samples. METHOD: Synovial tissues of 56 symptomatic OA and 49 RA patients were obtained. Two to three paraffin slides were used to quantify inflammation using haematoxylin and eosin (H&E) staining (synovitis score 0-9), and numbers of mast cells (per 10 high-power fields) using double immunofluorescence for CD117 and tryptase. Average scores per patient were used for analysis. Knee radiographs of OA patients were scored according to the Kellgren and Lawrence (KL) system and pain was determined in OA patients at baseline by visual analogue scale (VAS). RESULTS: Median (range) of mast cells was significantly higher in OA samples 45 (1-168) compared to RA samples 4 (1-47) (P-value < 0.001), despite a lower median (range) synovitis score in OA (2.5 (0-6.0)) compared to 4.6 (0-8.0) in RA samples. The synovitis score was significantly correlated with the number of mast cells (in OA Spearman's rho (P-value) 0.3 (0.023) and RA 0.5 (P-value < 0.001)). Interestingly, we observed a trend towards an association between the number of mast cells and an increased KL-grade (P-value 0.05) in OA patients, independently of synovitis. No associations were found with self-reported pain. CONCLUSION: Prevalence of mast cells in OA synovial tissue is relatively high and associates with structural damage in OA patients, suggesting a role of mast cells in this disease.

Differential TLR-induced cytokine production by human mast cells is amplified by FcɛRI triggering.

BACKGROUND: Mast cells are mainly present in strategic locations, where they may have a role in defence against parasites and bacteria. These pathogens can be recognized by mast cells via Toll-like receptors (TLR). Allergic symptoms are often increased in the presence of pathogens at the site of allergen exposure, but it is unknown which cytokines can mediate such an effect. OBJECTIVE: To study whether an interaction between IgE- and TLR-mediated activation of human mast cells can contribute to exacerbated inflammatory responses. METHODS: Peripheral blood-derived mast cells were stimulated with TLR ligands, in the presence or absence of anti-IgE triggering, after which degranulation was measured using flow cytometry and cytokine production was evaluated by multiplex assays, and ELISA. For evaluation of allergen-specific responses, mast cells were sensitized with serum of allergic individuals or controls, after which they were stimulated using allergens in combination with TLR ligands. RESULTS: Simultaneous triggering of mast cells via IgE and TLR ligands greatly enhanced cytokine production but not IgE-induced degranulation. Different TLR ligands specifically enhanced the differential production of cytokines in conjunction with FcεRI triggering. Importantly, only TLR-4 and TLR-6 were able to induce robust production of IL-13, an important molecule in allergic reactions. CONCLUSIONS & CLINICAL RELEVANCE: These results indicate that the simultaneous presence of pathogen- or danger-associated signals and FcεRI triggering via specific IgE can significantly modify mast cell-mediated allergic reactions via synergistic production of cytokines and inflammatory mediators and provide an explanation of augmented allergic symptoms during infection.

Toll-like receptor triggering augments activation of human mast cells by anti-citrullinated protein antibodies.

OBJECTIVE: Mast cells may play a role in rheumatoid arthritis (RA), but activation of human mast cells in autoimmune settings has been little studied. Toll-like receptors (TLR) and Fcγ receptors (FcγR) are important receptors for cellular activation in the joint, but expression and stimulation of these receptors in human mast cells or the functional interplay between these pathways is poorly understood. Here, we analysed triggering of human mast cells via these receptors in the context of anti-citrullinated protein antibody-positive (ACPA+) RA. METHODS: RNA and protein expression of TLRs and FcγR was quantified using PCR and flow cytometry, respectively. Mast cells were stimulated with TLR ligands (including HSP70) combined with IgG immune complexes and IgG-ACPA. RESULTS: Human mast cells expressed TLRs and produced cytokines in response to TLR ligands. Both cultured and synovial mast cells expressed FcγRIIA, and triggering of this receptor by IgG immune complexes synergised with activation by TLR ligands, leading to two- to fivefold increased cytokine levels. Mast cells produced cytokines in response to ACPA immune complexes in a citrulline-specific manner, which synergised in the presence of HSP70. CONCLUSIONS: Our data show that synovial mast cells express FcγRIIA and that mast cells can be activated by IgG-ACPA and TLR ligands. Importantly, combined stimulation via TLRs and immune complexes leads to synergy in cytokine production. These findings suggest mast cells are important targets for TLR ligands and immune complexes, and that combined activation of mast cells via these pathways greatly enhances inflammation in synovial tissue of RA patients.

Evidence for a functional role of IgE anticitrullinated protein antibodies in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a systemic autoimmune disease involving inflammation of the joints. Among the autoantibodies described in RA, anticitrullinated protein antibodies (ACPAs) are highly specific and predictive for RA. In addition, ACPAs have been implicated in the pathogenesis of RA. However, a direct functional response of immune cells from ACPA(+) RA patients toward citrullinated proteins has not been demonstrated. In this study, we show that exposure to citrullinated antigens leads to activation of basophils from ACPA(+) RA patients within 20 minutes. This was not observed after exposure of basophils to noncitrullinated control antigens or after stimulation of basophils from ACPA(-) RA patients and healthy controls. Basophil activation was correlated with the binding of citrullinated proteins to basophils. Furthermore, serum from ACPA(+) RA patients in contrast to that from ACPA(-) RA patients could specifically sensitize human FcepsilonRI expressing rat basophil cells (RBL), enabling activation by citrullinated proteins. Mast cell degranulation products such as histamine levels were enhanced in synovial fluid of ACPA(+) RA patients as compared with ACPA(-) RA and osteoarthritis patients. In addition, histamine levels in synovial fluid from ACPA(+) RA patients correlated with IgE levels, suggesting degranulation of mast cells by cross-linking IgE. Immunohistochemistry on synovial biopsies demonstrated an increased number of degranulated CD117(+) mast cells in ACPA(+) RA patients; IgE and FcepsilonRI expression in synovial mast cells from ACPA(+) RA patients was increased. In conclusion, our results show an immunological response of immune cells from ACPA(+) RA patients in a citrulline-specific manner. Moreover, these data indicate a role for IgE-ACPAs and FcepsilonRI-positive cells in the pathogenesis of RA.