A New Proposal of the Origin and Development of the Osteoclast

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This paper proposes our latest concept of the origin and development of the osteoclast, which is based on our previous experimental results as well as on an analytic review of the literature. We postulate that: (1) The osteoclasts are not derived from the hematopoietic cells but rather from local, non-hematopoietic cells, possibly undifferentiated mesenchymal cells. (II) Various phenomena occur during their developmental process. Namely, (1) The precursor cells of the osteo-clasts may take up the tritiated thymidine released from the disintegrated by-pertrophic chondrocytes during their early developmental stage; (2) the osteo-cytes and preosteoblasts are incorporated into the pre-existing osteoclasts; (3) cells with giant lysosomes also may be incorporated into the pre-existing osteo-clasts. This phenomenon appears to contribute to the increase in the percentage of area of giant lysosomes in the osteoclasts; (4) the blood-borne cells labelled with tritiated thymidine may be similarly incorporated into the pre-existing osteoclasts; (5) the transplanted cells either supply local Immoral factor for osteoclast function or fuse with the incompetent osteoclasts to activate them. Our new concept as described above appears to be the most reasonable one, integrating almost all the data from the previous experiments involving the use of various methods conducted by various researchers including ourselves.