Background T-cells play a key role in psoriatic arthritis (PsA). Nevertheless, the distribution and exact role of these cells remains unclear. Here, we study whether expanded T-cell clones are present in synovial tissue (ST), and whether such clones are also detectable in peripheral blood (PB) and synovial fluid (SF).

Methods ST and SF from inflamed knees was sampled in 2 PsA patients together with paired PB samples. Using next generation sequencing T-cell clones were identified by their unique T-cell receptor β-chain sequence. Clones with a frequency of ≥0.5% were arbitrarily considered to be expanded.

Results ST and SF samples from the same joint shared many of the expanded clones (see Table 1). Ninety percent (median, range 71-100%) of the expanded clones in ST were retrieved in SF, 33% of these being expanded in both samples. ST clones accounted for 14% of the SF T-cell repertoire. In PB 83% of the expanded ST clones were retrieved, 17% being expanded in both samples.

Analysis of both inflamed knees in patient 1 showed that 83% of the expanded ST clones in the left knee were retrieved in the right knee, 80% of these being expanded in both.

Conclusions In PsA synovial tissue harbors expanded T-cell clones, which are not fully represented in synovial fluid or blood samples. Preliminary analysis indicates that different joints contain identical expanded T cell clones. Our results suggest that in PsA comprehensive analysis of inflammation-related expanded clones best focuses on ST, rather than PB and SF.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.4456