Expression of Toll-like receptors 2 and 4 is increased in peripheral blood and synovial fluid monocytes of patients with enthesitis-related arthritis subtype of juvenile idiopathic arthritis.

Bacterial trigger possibly causes disease exacerbation in enthesitis-related arthritis (ERA) patients. Microbes initiate immune responses through Toll-like receptors (TLRs). We studied TLR expression on blood and SF monocytes and the effect of TLR ligands on peripheral blood (PB) mononuclear cells (PBMCs) in ERA patients. PB from 26 ERA patients and 19 healthy subjects and paired SF from 13 patients were collected. Dual-colour flow cytometry was done for TLR and CD14 expression. Results are expressed as median fluorescence intensity (MFI). Real-time PCR was done for TLRs. PBMCs were stimulated with lipopolysaccharide (LPS) or peptidoglycan and levels of IL-6 and MMP-3 measured in the culture supernatants. PBMCs from ERA patients had higher expression of TLR-2 [MFI 295.5 (48.1-598) vs 179 (68.7-442); P < 0.05] and TLR-4 [MFI 448 (178-2581) vs 402 (229-569); P < 0.05] as compared with controls. TLR-9 expression showed no significant difference between the two groups. In paired samples, SF mononuclear cells (SFMCs) had higher expression of both TLR-2 [MFI 485 (141-1683) vs 353 (118-598); P < 0.05] and TLR-4 [MFI 1016 (42.4-3159) vs 513 (193-2581); P < 0.05] as compared with PBMCs. Difference in TLR-9 expression was not significant. TLR RNA expression data were similar. Patients' PBMCs produced more IL-6 (13.51 vs 6.54 ng/ml) and MMP-3 (61 vs 32.9 ng/ml) as compared with those of the controls, on stimulation by LPS. With peptidoglycan also, IL-6 (30.58 vs 10.84) and MMP-3 (102.54 vs 49.45) were higher than in controls. Increased TLR-2 and TLR-4 expression on PBMCs and SFMCs may recognize microbial/endogenous ligands and up-regulate IL-6 and MMP-3 leading to disease exacerbation.