THE ROLE OF CELL-FUSION IN ERYTHROPOIESIS .2.

In a prior study, cell fusion was found to play an important part in e rythropoiesis in both the chicken and frog. Erythropoiesis in both org anisms could be traced back to groups of embryonic cells which first f used to form an aggregate structure consisting of multiple nuclei encl osed by a common cytoplasm. The cytoplasm of the fused aggregate under went dissolution to give rise to a set of denuded nuclei which, by man ufacturing a haemoglobinised cytoplasm, were transformed into erythrob lasts. Following these findings, the question of cell fusion in erythr opoiesis in the human was investigated, and the results are reported h ere. Leishman stained smears of marrow aspirate were used, and care ta ken to prevent the immature cells coming into contact with plasma. The reason for this was that plasma was found to alter the normal structu re of the immature haemopoietic cells, particularly the megakaryocyte series. Free from plasma contact, the nucleus of the megakaryocyte was found to be not multilobulated, but composed of a compact set of smal l nuclei. The mode of development of the megakaryocyte and its fate co uld be deciphered in the smears. The megakaryocytes arose as a result of fusion of small basophilic embryonic-like cells. After the megakary ocyte had attained a certain size, fusion ceased and the cytoplasm of the megakaryocyte underwent dissolution and was shed in the form of pl atelets, thus denuding the nuclei. The latter, bared of cytoplasm, wer e transformed directly into erythroblasts. The fate of the denuded nuc lei in this manner goes against the accepted view that the denuded nuc leus is phagocytosed. But phagocytosis is not observable, and, importa ntly, it is contrary to the principle of immunological tolerance. The conclusion is reached that the megakaryocyte in the human is the equiv alent of the fused aggregates in the chicken and frog, and erythropoie sis follows the same plan in all three organisms.