FAS LIGATION TRIGGERS APOPTOSIS IN MACROPHAGES BUT NOT ENDOTHELIAL-CELLS

The reticuloendothelial system includes macrophages and endothelial ce lls. These cells are produced and destroyed in vivo with a precision t hat implies the existence of homeostatic mechanisms. The stimuli for e ndothelial cell proliferation and monocyte production are becoming wel l characterized. However, the mechanisms involved in eliminating these cells are poorly understood. One mechanism involved in cellular elimi nation is apoptosis, which can be triggered in some cells by ligation of the Fas molecule. In this report we have investigated whether macro phages and endothelial cells express the Fas molecule, and whether Fas transmits an apoptosis-inducing signal in these cells. We demonstrate that macrophages express Fas and readily undergo apoptosis when cultu red with anti-Fas. In contrast, while endothelial cells can express th e Fas molecule, Fas ligation is insufficient to induce apoptosis. Thes e results suggest differential regulation of Fas function among cells of the reticuloendothelial system, and imply different mechanisms of h omeostasis.