Membrane-Bound Toll-Like Receptors are Overexpressed in Peripheral Blood and Synovial Fluid Mononuclear Cells of Enthesitis-Related Arthritis Category of Juvenile Idiopathic Arthritis (JIA–ERA) Patients and Lead to Secretion of Inflammatory Mediators

We examined expression and function of TLRs in enthesitis-related arthritis (ERA) patients. RNA levels of TLR1, TLR3, and TLRs 5–8 were measured in 24 ERA peripheral blood mononuclear cells (PBMC), 18 synovial fluid mononuclear cells (SFMC), and IRAK1, IRAK4, TRIF, TRAF3, and TRAF6 in 18 PBMC and 10 SFMC. IL-6 and IL-8 were measured in supernatants from ERA PBMC (n = 7), SFMC (n = 3), and healthy PBMC (n = 5) cultured with ligands for TLR1/2 (Pam 3-cys), TLR3 (poly I:C), TLR5 (flagellin), and TLR2/6 (zymosan). TLRs 1, 3, 5, and 6 were measured in whole blood (n = 20 ERA, seven healthy) and SFMC (n = 2) by flow cytometry. ERA PBMC compared to healthy PBMC and SFMC compared to ERA PBMC had higher RNA expression of TLR1, TLR3, TLR5, TLR6, IRAK1, IRAK4, TRIF, TRAF3, and TRAF6. TLR7 and TLR8 RNA expression was similar in all study groups. IL-6 and IL-8 levels were higher in stimulated ERA SFMC compared to ERA PBMC and in ERA PBMC compared to control PBMC. TLRs 1, 3, and 6 were also overexpressed at the protein level.