Takeshi Ohkita

FINE STRUCTURE OF HEPATIC SINUSOIDS and THEIR DEVELOPMENT IN HUMAN EMBRYOS and FETUSES

The fine structure of the hepatic sinusoids of 81 human embryos and fetuses and their development from 5 to 12 weeks gestation were studied. At 5 weeks gestation, sinusoid‐like structures and Kupffer‐like cells were observed between liver cell cords. Between 6 and 8 weeks gestation the sinuosids were completely developed. Definite Kupffer cells appear at this developmental stage, when the bone marrow has not yet formed. Floating macrophages form cell aggregates in the sinusoids which contact endothelial cells and settle as Kupffer cells. Erythroblastophagia is observed in Kupffer cells and macrophages. The endothelial linings are closed, with the attenuated cell processes and intercellular junctions between the adjoining endothelial cells. No transition was observed between Kupffer cells and endothelial cells. The findings suggest that Kupffer cells in the human embryo are extrahepatic in origin and that they reach the sinusoids via the circulatory system. Ito cells, which store fat, originate from mesenchymal cells in the septum transversum.

LIGHT AND ELECTRON MICROSCOPIC STUDIES ON THE DEVELOPMENT OF PERIPORTAL BILE DUCTS OF THE HUMAN EMBRYO

In order to clarify the development of periportal bile duct in the human embryo, the liver tissue of a 13 week‐old human embryo was studied using the electron as well as light microscope.

Leukemia and Thyroid Carcinoma Found among A-Bomb Survivors in Hiroshima

It is a well-known fact that various neoplasms can be induced by ionizing radiation. In humans, leukemia, and carcinomas of the skin, lung, thyroid gland, etc., have been reported among persons exposed to either total body or local irradiation, mostly for diagnostic and therapeutic purposes with X-rays. On the other hand, the final conclusion has not been reached yet, whether certain types of neoplasm were induced significantly by the atomic bomb explosions at Hiroshima and Nagasaki. But at present it is considered to be almost certain that leukemia and thyroid carcinoma were induced in high incidences by atomic bomb radiation. Induction of malignant lymphoma and carcinomas of the breast, ovary and lungs by atomic bomb irradiation is inconclusive and accepted by some and denied by others. For these reasons, presentation of data and discussion on this occasion will be limited to leukemia and thyroid carcinoma.

MORPHOLOGIC and RADIOLOGICAL OBSERVATIONS ON THE EARLIEST BONE MARROW FORMATION IN HUMAN EMBRYOS and FETUSES

Morphologic and radiologic studies were undertaken on 26 human embryos and fetuses to determine the stage and site of the earliest bone marrow formation. Up to the 10th week of gestation, primary bone marrow is not present anywhere although the intramembranous ossification occurs in the maxilla and mandible and also in the middle portion of the clavicle. At the 11th week of gestation, X‐ray examination showed in two fetuses the bone formation in the clavicle, scapula, maxilla, mandible, and the diaphysis of the long bones. Serial sections of these fetuses revealed that the primary bone marrow occurs first in the middle portion of the clavicle. From a series of our embryological studies, the concept of the mononuclear phagocyte system which involves the bone‐marrow‐derived monocytic origin of tissue macrophages, is not accepted, at least, on the origin of Kupffer cells in human fetal livers.

In vitro chemosensitivity tests on human tumor xenografts by clonogenic assay: the combined use of mitomycin C with α-interferon or γ-interferon

Using the human tumor clonogenic assay technique, the effects of Mitomycin C plus either α-interferon or γ-interferon were studied against five human tumor xenografts serially transplanted into nude mice (three gastric and two colon cancers). When the survival fraction found with the drug combination was smaller than the multiplication of survival fractions with either drug alone, the combined effect was defined as synergism. Similarly, antagonistic effect was defined when the survival fraction of drug combination was larger than the larger one observed in either interferon or Mitomycin C alone. Four out of five human tumor xenografts (three gastric and one colon cancers) showed synergistic effects in combination of α-interferon with Mitomycin C. Though two gastric cancer xenografts exhibited synergistic effects in combination of γ-interferon with Mitomycin C, antagonistic effects, which was not found in combination of α-interferon with Mitomycin C, were observed in one gastric cancer and one colon cancer xenografts.