Electron Microscopic Studies on the Spleen of Normal Mouse and its Morphological Changes after Total Body Irradiation

Abstract

Electron microscopic observations of the normal mouse spleen confirm the reticular cells having an important role on erythropoiesis and lymphocytopoiesis. The possibility of DNA reutilization is discussed in connection with phagocytic bodies (Phagosomes) which are derived from phagocytized nuclear substance.
A special lock-gate-like structure of the sinus wall is observed and it is considered that this makes possible to form blood channels between the pulp cord and sinus by an open-and-close mechanism depending upon the situation needed.
Comparing with the normal structure, the changes in the mice spleen after total body irradiation of 1, 000 r were studied, and the following results were obtained.
(1) Half an hour after the irradiation, the formation of clear foci is prominent in the nucleus, cytoplasma and mitochondrial matrix of the lymphocytes. As the time passes after irradiation, the clear foci in the cytoplasma disappear and focal aggregation of chromonema occurs, which tends to increase in its intensity. These changes are considered to be based on the alteration of molecular structure of the constituents caused by X-ray irradiation.
(2) Two hours after irradiation, the reticular cells adhere to the lymphocytes and by the activity of the former, the latter are dehydrated and condensed. In the next step, the condensed lymphocytes are phagocytized and digested by the reticular cells.Formation of the so-called tingible bodies seen histologically only occur when the reticular cells could participate in this phenomenon.
(3) In the red pulp, a part of the myeloid cell elements is phagocytized by the same mechanism of the reticular cells and other parts will flow out from pulp cord to sinus space through the opening of lock-gates of endothelial cells at the sinus wall.