Objective: Lymphoid neogenesis seems to play an important role in the persistence of chronic inflammation and has been shown in various disorders characterized by chronic inflammation including rheumatoid arthritis. Arthritis of Behçet's disease is characterized by non-erosive arthritis in which the disease course is considered to be subacute and self limiting. However, molecular mechanisms underlying those features of Behçet's arthritis have not been defined yet. In order to determine the contribution of lymphoid neogenesis in the disease course of Behçet's arthritis, we investigated the synovial fluid (SF) levels of CXCL 12, CXCL 13, CCL 21 homeostatic chemokines and the percentage of SF naive lymphocytes expressing their receptors such as CXCR4+ and CCR7+. We further measured the SF TGF-Beta and INF-Beta levels which are known to contribute lymphoid neogenesis via leading persistent expression of CXCR4 on T cells and inhibiting T cell apoptosis, respectively.
Methods: Fifty-one [15 BD, 17 RA, and 19 osteoarthritis (OA)] patients with at least one- sided knee arthritis were enrolled in the study. Patients with BD constituted the study group, and RA, OA patients were used as positive and negative control groups, respectively. The SF levels of CXCL 12, CXCL 13, CCL 21, TGF-Beta and INF-Beta were measured by ELISA. CXCR4, CCR7 chemokine receptors on SF lymphocytes were tested by Flow- cytometry. Kruskal-Wallis test and Mann-Whitney U test were used for statistical analysis where appropriate.
Results: Synovial fluid CCL 21 levels were found to be increased in RA patients as compared to BD and OA patients (p = 0.003, and p = 0.013, respectively). No significant difference was detected between BD and OA patients with respect to CCL 21 levels. Both CXCL 12 and CXCL 13 SF levels were found to be higher in RA and BD patients as compared to OA patients (CXCL-12; p = 0.012, and p = 0.024), (CXCL 13; p < 0.001, and p = 0.007). However, no difference with regard to SF levels of both CXCL 12 and CXCL 13 were found between RA and BD patients. Percentages of both CD3+CXCR4+ lymphocytes and CD3+CCR7+ lymphocytes in the SF of RA patients were detected to be increased as compared to those of BD and OA patients (CD3+CXCR4+; p = 0.019, p = 0.048, respectively), (CD3+CCR7+; p = 0.023, p = 0.001, respectively). However, no differences with respect to the percentages of SF lymphocytes expressing CD3+CXCR4+ or CD3+CCR7+ were found between BD and OA patients. Both TGF-Beta and INF-Beta SF levels were found to be higher in RA patients as compared to BD and OA patients (TGF-Beta; p = 0.041, and p = 0.003), (INF-Beta; p = 0.012, and p = 0.016). However, no differences with regard to SF levels of both TGF-Beta and INF-Beta were found between BD and OA patients.
Conclusion: Considering the subacute, self limiting and non-erosive course of arthritis observed in BD, our finding of detection of lower levels of CCL21 and TGF-Beta1 and IFN-Beta in BD patients, seems to prevent the development of LN and chronic inflammation in Behçet's synovitis. In support of this view, percentages of SF naïve T lymphocytes were found to be lower in BD patients comparing with those of the RA. Absence of tertiary lymphoid structures in BD patients, may explain the spontaneous resolution of Behçet's arthritis in most of the cases.