Destruction of circulating leukemia cells by phagocytosis in rats with myelogenous leukemia

Acute myelogenous leukemia was induced in outbred Long-Evans rats by iv injections of leukemia cells from a subcutaneous tumor of Shay myelogenous leukemia. In rats with this leukemia the peripheral white blood cell (WBC) counts varied from 2.4 to 700 X 10(9)/liter. No differences were found in the bone marrow of the rats with the high WBC counts and that of rats with low WBC counts. This observation could explain the large variations in the number of circulating leukemia cells caused by differences in cell proliferation or delivery of cells into the circulation. Massive phagocytosis of leukemia cells occurred in animals with low WBC counts (less than 12 X 10(9)/liter) but not in animals with high WBC counts (greater than 150 X 10(9)/liter). This phagocytosis was directed against circulating leukemia cells. The main phagocytes were Kupffer's cells of the liver and macrophages of the spleen parenchyma. In addition, phagocytosis occurred in the spleens and bone marrow by intravascular macrophages, which were derived from extravascular sites. The endothelium of the postcapillary venules of the lymph nodes participated in the phagocytosis of circulating leukemia cells while continuing to be the locus of lymphocytic return from circulation to lymphatic parenchyma. The factors underlying the differences in macrophage activity between the rats with high and low WBC counts were unknown.

On the development of the lymphoid follicles of the bursa of Fabricius

The structural features of the development of the bursa of Fabricius in white Leghorn chick embryos are depicted at carefully timed intervals during embryogenesis, with emphasis on the sequence of events between the ninth and twelfth days of incubation. The direction and character of the migration of lymphoid cell precursors and granulocytes from the intravascular space to intraepithelial sites, where the formation of the primitive lymphoepithelial nodule takes place, is demonstrated. The mechanism of the mode of migration of these cells through the stromal epithelial interface is described and illustrated with electron micrographs and their role in the development of the primitive lymphoid follicles is described and discussed.

Passage of red blood cells through the sinusoidal wall of the spleen

The migration of blood cells across the wall of splenic sinusoids has been studied by means of serial sections in rats inoculated with murine erythroblastosis virus (MEV). The sinusoidal walls of the normal spleen have no permanent openings. In the normal spleen, mature red blood cells and blood cells in the latest stages of maturation can be seen in diapedesis. The predominant form of transmural migration is intercellular. In MEV-inoculated animals, in which there is a vigorous erythroblastic proliferation, large numbers of erythroblasts are in transmural passage. Serial sections show that these cells migrate through the cytoplasm of the endothelial lining cells. On the basis of these observations, it is suggested that the transcellular mode of migration may be related to the delivery of newly formed red blood cells into the circulation while the intercellular mode may be part of the mechanism by which the spleen controls the removal of red cells from the circulation.