Fas-induced in vivo Apoptosis in Bone Marrow: Anti-Fas mAb-induced Elimination and Successive Proliferation of Fas-expressing Cells Especially Those of Myeloid Lineage

Abstract

A single administration of agonistic anti-Fas mAb RK8 into mice decreased the number of bone marrow cells especially Mac1⁺ and Gr1⁺ Cells of myeloid lineage. These cells, which were shown to be Fas-positive in normal bone marrow, were directly eliminated in vivo by Fas-mediated apoptosis. After the elimination of Fas-positive bone marrow cells, bone marrow was reconstituted by successive increase of numbers of Grl^low and Macl^low myeloid precursor cells expressing high levels of Fas, which are minor constituents in normal bone marrow. The increased cells consisted at least two compotents, Grl^dull Macl⁺ cKit⁺ cells and Grl^{intermediated} Macl⁺ cKit^- cells, both of which were shown to be sensitive to Fas-induced apoptosis in vivo. Thus, Fas is functional in normal bone marrow and Fas-induced apoptosis in bone marrow enhances marked proliferation of Fas-expressing myeloid precursor cells in vivo.