['ATP-binding cassette transporter A1 (ABCA1) is critical in exporting cholesterol from macrophages and plays a protective role in the development of atherosclerosis. This study was to determine the effects and potential mechanisms of Chlamydia pneumoniae (C.\xa0pneumoniae) on ABCA1 expression and cellular cholesterol efflux in THP-1 macrophage-derived foam cells.', 'C.\xa0pneumoniae significantly decreased the expression of ABCA1 and reduced cholesterol efflux. Furthermore, we found that C.\xa0pneumoniae suppressed ABCA1 expression via up-regulation of miR-33s. The inhibition of C.\xa0pneumoniae-induced NF-κB activation decreased miR-33s expression and enhanced ABCA1 expression. In addition, C.\xa0pneumoniae increased Toll-like receptor 2 (TLR2) expressions, inhibition of which by siRNA could also block NF-κB activation and miR-33s expression, and promot the expression of ABCA1.'] Does chlamydia pneumoniae negatively regulate ABCA1 expression via TLR2-Nuclear factor-kappa B and miR-33 pathways in THP-1 macrophage-derived foam cells?