A New Stereological Method for Determination of the Size of Spherical objects in Electron Microscopy: Its Application to Small Lymphocytes of the Mouse Thymus

Abe, Kazuhiro; Ito, Takashi

doi:10.1679/aohc1950.34.203

Cited by 13 publications

(7 citation statements)

References 10 publications

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“…There is evidence indicating that cortical and medullary small lymphocytes in the thymus are different in certain morphological and behavioral aspects (TROWELL, 1961;ITO and HOSHINO, 1962;KOSTOWIECKI and SHERMAN, 1963;SAINT-MARIE and LEBLOND, 1964;WEBER, 1966;ABE, SASAKI and ITO, 1972a). In previous papers we also observed by electron microscopy that thymic small lymphocytes are different in ultrastructural features between cortex and medulla ITO, 1970b, 1972;ABE, SASAKI and ITO, 1973b). The morphological difference between cortical and medullary small lymphocytes is considered a reflection of their functional differentiation, because it is assumed that cortical small lymphocytes are immunologically incompetent and medullary small lymphocytes, competent.…”

Section: Discussionmentioning

confidence: 57%

Vascular Permeability in the Thymus of the Mouse

Abe

Ito

1974

Arch. Histol. Jap., Arch. Histol. Jpn

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Summary. In this study, thymic blood vessels in adult mice were examined particularly in relation to the permeability of their walls. The pattern of distribution of the thymic vessels indicated that the cortex is supplied, for the most part, with capillaries, and the medulla with venules.Cortical capillaries and medullary venules are usually encircled by epithelial reticular cells, but the investment is not completely continuous. Endothelial cells of cortical capillaries and medullary venules contain numerous micropinocytotic vesicles. In addition, larger vacuoles are also seen in the endothelial cells of the venules. After intravenous injection of ferritin, these micropinocytotic vesicles and vacuoles in the endothelial cells of the thymic vessels are labeled by ferritin. Ferritin particles also appear in the perivascular spaces of the thymic vessels. The vascular permeability in the thymus is different between cortical capillaries under the capsule, capillaries in the inner cortex and venules in the medulla. The injected ferritin in only limited amounts also invades the thymic parenchyma especially in the outermost cortex and the medulla. The permeability of ferritin across the walls of thymic blood vessels was compared with that in the splenic lymphatic tissue, mesenteric lymph node and pancreas. The results obtained were discussed with special reference to the vascular barrier mechanism in the thymus.The existence of a blood barrier in the thymus has been postulated on the basis of the earlier findings that the thymus, unlike other lymphatic organs, does not show significant histologic changes associated with immune reactions to blood-borne antigens, whereas it responds to antigens injected directly into the organ (MARSHALL and WHITE, 1961). The barrier was previously thought to be ultrastructurally established by a continuous investment of epithelial reticular cells around the walls of the thymic blood vessels (CLARK, 1963;WEISS, 1963). However, it has been demonstrated by closer electron microscopy that the epithelial reticular cells are not completely continuous around the thymic blood vessels (ITO and HOSHINO, 1966). It should also be examined, however, whether or not blood-borne antigens actually permeate the vascular walls in the thymus, because failure of the thymic parenchyma to respond to antigens may account for the "non-permeable" vascular walls. Recently RAVIOLA and KARNOVSKY (1972) have assessed in detail, by electron microscopy, the permeability of the thymic vessels to ultrastructural tracers of different molecular weight including ferritin.In this study, we examined the permeability across the walls of thymic blood vessels by using ferritin as tracer. The choice of ferritin afforded, as shown in the present results, not only qualitative but also semiquantitative evaluation of the vascular permeability in electron microscopy. Material and Methods A total of 59 dd-mice of both sexes, two months old, were used. For examination of the pattern and distribution of the thymic vessels, 10 mice were...

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