High in vivo expression of interleukin-17 receptor in synovial endothelial cells and chondrocytes from arthritis patients

Objective. To evaluate the presence of interleukin-17 (IL-17) and the expression of IL-17 receptor (IL-17R) in joint tissues from subjects with different arthritides. Methods. Immunohistochemistry was used on frozen synovial and cartilage biopsies to identify cells expressing IL-17 and IL-17R. Results. IL-17 staining was present only in synovial biopsies of rheumatoid arthritis (RA) (seven out of nine cases). IL-17R was expressed by all synovial biopsies evaluated except for three cases of post-traumatic arthritis (PTA). Vascular endothelial cells mainly expressed IL-17R. The percentage of IL-17R(+) vessels was the highest in RA synovium and the lowest in PTA. Chondrocytes from all types of arthritides were negative for IL-17 staining, but expressed IL-17R; the highest percentage of positive chondrocytes was found in seronegative spondylarthritis and the lowest in RA. Conclusions. IL-17-positive cells are found exclusively in RA. On the other hand, synovial endothelial cells and chondrocytes expressing IL-17R are found in the majority of patients with different types of arthritis. This finding suggests a role for a second ligand for IL-17R, which could be either a different cytokine or a different isoform of IL-17.