Human scavenger receptor B1 is involved in recognition of apoptotic thymocytes by thymic nurse cells

Recognition and uptake of apoptotic cells by neighboring phagocytes is esse ntial for the clearance of dying cells without accompanying inflammation or tissue damage. In the thymus, many apoptotic cells are generated in the pr ocess of negative selection, and both thymic macrophages (professional phag ocytes) and nursing thymic epithelial cells (nursing TEC; nonprofessional p hagocytes) recognize and ingest them. However the receptors responsible for this recognition and uptake have not been identified. In the present study , we have established a human nursing TEC line and examined the expression of several genes of the scavenger receptor family considered to be potentia l receptors for apoptotic cells. Human scavenger receptor-Ri (hSR-B1)/CLA-1 , previously shown to recognize apoptotic cells, was strongly expressed in nursing TEC, whereas there was little or no expression of the other scaveng er receptors tested: scavenger receptor class A, CD36, or CD68. Suppression of hSR-B1/CLA-1 expression using antisense oligonucleotides decreased the binding of apoptotic thymocytes to nursing TEC by more than 40%. These resu lts indicate that hSR-B1/CLA-1 may play a major role in the clearance of ap optotic cells in the thymus, mediating the recognition and ingestion of apo ptotic thymocytes by nursing TEC.