DISTRIBUTION OF MURINE MANNOSE RECEPTOR EXPRESSION FROM EARLY EMBRYOGENESIS THROUGH TO ADULTHOOD

The mannose receptor is a 175-kDa transmembrane glycoprotein that appe ars to be expressed on the surface of terminally differentiated macrop hages and Langerhans. cells. The ectodomain of the mannose receptor ha s eight carbohydrate recognition domains. The receptor recognizes the patterns of sugars that adorn a wide array of bacteria, parasites, yea st, fungi, and mannosylated ligands. Clearance studies in whole animal s have localized radiolabeled ligands, such as mannosylated bovine ser um albumen, not only to macrophages, but also to liver sinusoidal endo thelial cells. Hitherto, there has been no comprehensive analysis of e xpression of the mannose receptor in embryonic and adult mouse tissues . In this study, we have undertaken a systematic survey of the express ion of the mannose receptor from early embryogenesis through to adulth ood. The mannose receptor is expressed on tissue macrophages throughou t the adult mouse as expected. However, the mannose receptor is first observed on embryonic day 9 on cells that line blood island vessel wal ls in the yolk sac. The mannose receptor is localized on sinusoidal en dothelial cells in embryonic liver by embryonic day 11 and in bone mar row at embryonic day 17. This pattern persists in these organs through out embryogenesis into adulthood when sinusoidal endothelial cells of lymph nodes also express the mannose receptor. The receptor is also fo und on lymphatic endothelial cells of small intestine. In contrast, si nusoids of spleen and thymus do not express mannose receptor antigen. This study demonstrates that the mannose receptor is expressed on tiss ue macrophages and on subsets of vascular and lymphatic endothelial ce lls. Thus, the mannose receptor maybe a marker of the so-called reticu loendothelial system.