Cholinesterase as a possible marker for early cells of the megakaryocytic series.

Among marrow cells of rats only megkarsevere thrombocytopenia by injection of yocytes stain appreciably for acetylantiplatelet antiserum. Subsequently, the cholinesterase. An investigation was number of recognizable megakaryocytes therefore undertaken to determine whether increased, suggesting their derivation from this staining characteristic might be used the small acetylcholinesterase-positive to identify precursors of recognizable cells. These results suggest that acetylmegakaryocytes. Marrow cells smaller cholinesterase activity can be used as a than recognizable megakaryocytes were marker for megakaryocytic cells that canpositive for the enzyme. The number of not be detected with conventional staining these cells increased after induction of methods. M EGAKARYOCYTES ARE platelet-producing, polyploid cells of the hemopoietic tissues. Although these cells have been studied increasingly during the past few years, their immediate precursors have not been identified and characterized. In 1954 Zajicek,’ using Koelle’s method, detected acetylcholinesterase (AChE) activity histochemically in the blood and hemopoietic cells of several different mammalian species. In the cat and rat, AChE activity was confined almost exclusively to megakaryocytes and platelets with very little activity in the erythroid series and none in leukocytes. Zajicek also reported that with prolonged substrate incubation some of the needle-shaped crystals characteristic of AChE activity formed over a small number of cat bone marrow cells that were smaller than megakaryoblasts. He was, however, unable to demonstrate conclusively that these small cells were related to megakaryocytes, largely because of limitations of the Koelle thiocholine method, especially the formation of nonspecific stain deposits (after prolonged substrate incubation). In 1964 Karnovsky and Roots2 introduced a direct-coloring thiocholine method for detecting AChE that eliminated many of the problems associated with Koelle’s method. Experiments were therefore designed to examine whether the presence ofAChE, as detected by the Karnovsky and Roots method, might be used to identify early stages of the megakaryocytic series. This study will demonstrate that AChE-positive cells smaller than recognizable megakaryocytes are present in rat bone marrow. The number of these small AChE cells increases rapidly after the induction of severe thrombocytopenia. This increase is followed by a similar increase both in the number of recognizable megakaryocytes and in their mitotic index.