Toll-like receptor (TLR) 2 is upregulated on peripheral blood monocytes of patients with psoriatic arthritis: a role for a gram-positive inflammatory trigger?

Toll-like receptor (TLR) 2 and TLR4 are able to activate innate immune cells in response to gram-positive and gram-negative bacteria, respectively. Psoriatic arthritis (PsA) is a chronic inflammatory joint disease and gram-positive streptococcus may have a role in its pathogenesis, suggesting the importance of TLR2 stimulation in PsA. Objective To assess TLR2 and TLR4 expressions on innate immune cells of PsA patients, relating to clinical disease activity. Methods Fort-five patients with peripheral joint manifestations of PsA were included and disease activity was assessed by Disease Activity Score of 28 joint counts (DAS28). 32 healthy subjects constituted the control group. Membrane-bound TLR2 and TLR4 expressions were assessed on peripheral blood monocytes and neutrophils by flow cytometry. Results Twenty-seven patients had active PsA (DAS28 higher than 2.6) and 18 had inactive disease. TLR2 was significantly upregulated on monocytes in both active and inactive PsA group, comparing to healthy controls. TLR4 was similarly expressed in all tested groups. Conclusion TLR2 is overexpressed by PsA monocytes, suggesting that gram-positive exposure could induce higher inflammatory responses in this disease.