Retinol-binding protein that mediates retinol transport in blood plasma. Delivers retinol from the liver stores to the peripheral tissues. Transfers the bound all-trans retinol to STRA6, that then facilitates retinol transport across the cell membrane. Interacts with TTR. Interaction with TTR prevents its loss by filtration through the kidney glomeruli. Interacts with STRA6. Produced between days 10 and 15 of pregnancy and at day 15 found in both the peri-implantation conceptus (trophectoderm and yolk sac) and the endometrial surface and glandular epithelium. Found in allantoic fluid at day 30 of gestation. Belongs to the calycin superfamily. Lipocalin family.