OBJECTIVE The purpose of this study was to assess the role of macrophage OSBP-related protein 1L (ORP1L) in the development of atherosclerosis. METHODS AND RESULTS C57BL/6 mice overexpressing human ORP1L in macrophages driven by scavenger receptor A promoter were generated. Bone marrow (BM) of the mice was transplanted into LDLr-/- animals, and aortic root lesion area in the recipients was determined after Western-type diet feeding. The recipients of ORP1L BM displayed 2.1-fold increase (P<0.001) in lesion size as compared with recipients of wild-type littermate BM. Macrophages of the ORP1L BM recipients showed a decrease in ABCG1 and APOE mRNAs and proteins, and an increase in PLTP message; also the plasma PLTP activity was elevated. The effect of ORP1L on cholesterol efflux was assessed using macrophages loaded with [3H]cholesterol oleate-acLDL or labeled with [3H]cholesterol. The ORP1L transgenic macrophages displayed 30% reduction (P<0.01) in cholesterol efflux to HDL2, but not to apoA-I. ORP1L was shown to bind 25- and 22(R)-hydroxycholesterol, identifying it as an oxysterol binding protein. Furthermore, ORP1L attenuated the response of ABCG1 mRNA to 22(R)-hydroxycholesterol, the effect on ABCA1 being less pronounced. CONCLUSIONS The results demonstrate that macrophage ORP1L can act as a modulator of atherosclerotic lesion development and provide clues to the underlying mechanism.