Objective: 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.
Methods: 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.
Results: 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.
Conclusion: 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.