Characterization of the expression of TLR2 (Toll-like receptor 2) and TLR4 on circulating monocytes in coronary artery disease

TLRs are receptors involved in the recognition of pathogens by the innate immune system, and TLR2 and TLR4 play important roles in the activation of monocytes. A total of 105 consecutive patients who underwent coronary angiography comprised of 46 with stable effort angina (SA), 41 with unstable angina (UA), and 18 with no significant CAD (CNT) were enrolled. The baseline expression levels of TLR2 and TLR4 on monocytes in peripheral blood mononuclear cells (PBMCs) were determined by flowcytometric analysis. Since TLR2 expression has been reported to be regulated by TLR4 signaling, we cultured PBMCs with or without lipopolysaccharide (LPS, 1 mu g/ml). At baseline, TLR4 levels (mean of fluorescence intensity) in SA (145 +/- 58, p < 0.05) and UA (164 +/- 65, p < 0.01) were higher than those in CNT (107 +/- 37). As for TLR2, levels were higher in UA (108 +/- 36, p < 0.05) than in SA (94 +/- 18) and CNT (87 +/- 22). After stimulation with LPS, TLR2 levels increased in SA but decreased in UA. In conclusions, TLR4 levels increased in both SA and UA. Monocytes in UA were characterized by elevated TLR2 levels and unresponsiveness of the TLR2 levels to TLR4 stimulation.