THE SPECIFIC RECOGNITION BY MACROPHAGES OF CD8(+),CD45RO(+) T-CELLS UNDERGOING APOPTOSIS - A MECHANISM FOR T-CELL CLEARANCE DURING RESOLUTION OF VIRAL-INFECTIONS

During viral infections, CD8(+),CD45RO(+) T populations expand. These primed cells express abundant levels of cytoplasmic granules that contain perforin and TIA-1. Recent work has suggested that the majority of this CD8(+) population downregulates Bcl-2 protein expression and is destined to undergo apoptosis. In this study we have investigated the elimination of these apoptotic CD8(+) T cells by both human monocyte-derived and murine bone marrow macrophages. We have found that these phagocytes recognize and ingest both apoptotic CD8(+) and CD4(+) T cells using an alpha(v) beta(3) (vitronectin receptor)/CD36/thrombospondin recognition system, with the same receptors being used in the recognition of apoptotic neutrophils. These data provide new evidence for a mechanism that enables the clearance of greatly increased populations of CD8(+) effector cells which are found during viral infections. This enables cellular homeostasis to occur in the host upon resolution of viral diseases in vivo.