Rheumatoid arthritis synovial fibroblasts produce a soluble form of the interleukin-7 receptor in response to pro-inflammatory cytokines

We previously demonstrated that baseline synovial overexpression of the interleukin-7 receptor α-chain (IL-7R) is associated with poor response to tumour necrosis factor (TNF) blockade in rheumatoid arthritis (RA). We found that IL-7R gene expression is induced in fibroblast-like synovial cells (FLS) by the addition of TNF-α, IL-1β and combinations of TNF-α+ IL-1β or TNF-α+ IL-17, thereby suggesting that these cytokines play a role in the resistance to TNF blockade in RA. Because FLS and CD4 T cells also produce a soluble form of IL-7R (sIL-7R), resulting from an alternative splicing of the full-length transcript, we wondered whether expression of sIL-7R is similarly regulated by pro-inflammatory cytokines. We also investigated whether sIL-7R is detectable in the serum of RA patients and associated with response to TNF blockade. RA FLS were cultured in the presence of pro-inflammatory cytokines and sIL-7R concentrations were measured in culture supernatants. Similarly, sIL-7R titres were measured in sera obtained from healthy individuals, early untreated RA patients with active disease and disease-modifying anti-rheumatic drug (DMARD)-resistant RA patients prior to initiation of TNF-blockade. Baseline serum sIL-7R titres were correlated with validated clinical measurements of disease activity. We found that exposure of RA FLS to pro-inflammatory cytokines (TNF-α, IL-1β and combinations of TNF-α and IL-1β or TNF-α and IL-17) induces sIL-7R secretion. Activated CD4 T cells also produce sIL-7R. sIL-7R serum levels are higher in RA patients as compared to controls. In DMARD-resistant patients, high sIL-7R serum concentrations are strongly associated with poor response to TNF-blockade. In conclusion, sIL-7R is induced by pro-inflammatory cytokines in RA FLS. sIL-7R could qualify as a new biomarker of response to therapy in RA.