Background/Purpose:

We have previously shown that there is an increase in IL-17 in the synovial fluid of patients with Reactive arthritis(ReA) and undifferentiated spondyloarthropathy(uSpA). Besides Th17 cells, IL-17 is produced by several innate cells such as NK, NKT , γδT and double negative T cells(DNT) To account for increased IL-17 we have enumerated these innate cells in the peripheral blood and synovial fluid of patients with ReA/uSpA.  

Methods:

Patients were labelled as Reactive arthritis if they had a typical clinical history of acute or subacute onset of asymmetrical oligoarthritis with a preceding history of diarrhoeal illness within 4 weeks and as uSpA if patients fulfilled ESSG criteria but didnot fit into any defined spondyloarthropathy.  10 to 30 ml of Synovial fluid was aspirated from the inflammed knee joint prior to corticosteroid injection along with peripheral blood in EDTA for cell analysis.   Peripheral blood (PB) of  28 patients with ReA/uSpA and  paired synovial fluid (SF)in 20 patients were collected between September 2014 and  June 2015 for analysis.  The percentage of  NK cells(CD56+CD3-)/NK cells(CD56^bright) / NK cells(CD56^dim) / NKT cells(CD3+/CD56+) , DNT cells(CD4^–/CD8^– αβTCR+CD3+)and γδT cells(γδTCR+CD3+)  were determined by flow cytometry (Beckman Coulter, USA)  using a panel of monoclonal antibodies (BD biosciences, USA)   In paired samples the percentage of cells were compared between the synovial fluid and peripheral blood by non parametric tests(Wilcoxon signed ranks test)

Results:

28 patients(male-25 female–3) with a median age 24(IQR 20-31) years were recruited .Of these 12 were ReA and 16 were uSpA.4 patients had chronic symptoms whereas 24 had acute episode.Knee was the most common joint involved followed by ankle.11 patients had evidence of enthesitis (most common-achilles tendinitis)whereas 3 patients had extra-articular involvement. The median frequency and interquartile range  of various cell population in the peripheral blood and synovial fluid are presented in Table 1.

Table 1.  Percentage (median and interquartile range) of various innate cells in peripheral blood and synovial fluid

** p < 0.005  * p <0.05

CD56 ^bright NK cells was significantly increased in synovial fluid(p=.000) and CD56 ^dimNK cells was significantly decreased in synovial fluid(p=0.001) in comparison to peripheral blood. As it is known that CD56 bright NK cells can produce IL17 , these cells can be a innate source of IL17 in the inflamed joints.Also γδT cells was significantly increased in peripheral blood (P=.022).

Conclusion:

CD56 ^bright NK cells which are cytokine producers are expanded in the synovial compartment as compared to peripheral blood and may be contributing to the production of IL-17 in ReA and uSpA. The increase of peripheral blood γδT cells is most likely related to its origin from the gut.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-subset-of-natural-killer-cells-are-expanded-in-synovial-fluid-of-patients-with-reactive-arthritis-and-undifferentiated-spondyloarthritis/