Lysosomal changes in epithelial cells of the mouse thymus after hydrocortisone treatment

Effects of hydrocortisone on the ultrastructure of the thymic cysts of chicks

Thymi from 10-day old male chicks injected subcutaneously with 5 mg of hydrocortisone for 2 consecutive days and sacrificed on the 4th day were examined by electron microscopy. With depletion of the lymphoid cells, cystic structures, consisting of inter- and intracellular cysts are more apparent in the hydrocortisone-treated chicks. The intercellular cysts vary in size and shape and are lined by cystic, endocrine-like and lymphoid cells. Luminal surfaces of the cystic cells contain microvilli. The lateral plasma membranes show complex interdigitations. The prominent terminal web contains vesicles and numerous core rootlets. Frequent membrane invaginations are apparent at the bases of the microvilli. The endoplasmic reticulum and the Golgi complex are moderately developed. Mitochondria are variable in number but are numerous in some cells. The cytoplasm also contains dense bodies, vacuoles and myelin figures. Endocrine-like cells, containing numerous secretory granules and bordering directly on the follicular lumen suggest that their secretion may be discharged into the lumen. Cystic cells containing intracellular cysts are observed. Presence of cleft-like spaces, microvilli closely opposed to adjacent cytoplasmic processes or lateral microvilli may reflect responses to increase in absorptive or transport function. The present data suggest that hydrocortisone may modulate the structure and function of the cystic structures in the chick thymus.

The ANAE reaction pattern of reticular stromal cells of lymphatic organs from normal and hydrocortisone--treated mice

The pattern of alpha-naphthyl-acetate esterase (ANAE) activity in stromal and lymphatic cells has been examined in lymphatic organs from normal and hydrocortisone (HC)-treated mice. The distribution of ANAE-positive lymphocytes as well as stromal cells in peripheral lymphatic organs was different in T- and B-dependent regions, while in the thymus there was the difference between cortex and medulla. The HC application evoked a marked changes in the pattern of ANAE-positive cells distribution of the thymus, producing only a slight ones in the remaining organs. The influence of HC on the ANAE reaction intensity and distribution in the examined tissue sections is discussed.

The ultrastructure of the normal human thymus: a study of 36 cases

Electron microscopy of the normal human thymus demonstrates a supporting framework of epithelial-reticular cells with long branchticular cell processes lie lymphocytes, macrophages, and rare myoid cells. Both small and large lymphocytes are evident. No desmosomes are observed between the lymphocytes and the epithelial-reticular cells. Macrophages are most numerous in the cort(x were they often contain phagocytized nuclear debris. The possible functional significance of the above-described fine structural features is discussed.

Morphological and enzyme-histochemical changes of the mouse thymus after hydrocortisone

This study was designed to determine the effect of hydrocortisone on morphology and enzyme-histochemistry of the thymus, on the peripheral blood cell picture, and on skin graft survival time in mice. In addition to the prolongation of survival of skin grafts, to a dose-dependent lymphopenia, and to an increase in the number of circulating neutrophil granulocytes, we found morphologically enlarged epithelial reticular cells with large cytoplasmic vacuoles, which often formed cyst-like structures. Because of their broad enzyme activity it may well be that these epithelial cell derived cysts regulate by means of humoral factor(s) the repopulation of the thymic cortex. In addition semithin sections clearly showed that the polymorphonuclear-like cells in the thymic cortex are altered lymphocytes with fragmented nuclei.

Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics

The term apoptosis is proposed for a hitherto little recognized mechanism of controlled cell deletion, which appears to play a complementary but opposite role to mitosis in the regulation of animal cell populations. Its morphological features suggest that it is an active, inherently programmed phenomenon, and it has been shown that it can be initiated or inhibited by a variety of environmental stimuli, both physiological and pathological.The structural changes take place in two discrete stages. The first comprises nuclear and cytoplasmic condensation and breaking up of the cell into a number of membrane-bound, ultrastructurally well-preserved fragments. In the second stage these apoptotic bodies are shed from epithelial-lined surfaces or are taken up by other cells, where they undergo a series of changes resembling in vitro autolysis within phagosomes, and are rapidly degraded by lysosomal enzymes derived from the ingesting cells.Apoptosis seems to be involved in cell turnover in many healthy adult tissues and is responsible for focal elimination of cells during normal embryonic development. It occurs spontaneously in untreated malignant neoplasms, and participates in at least some types of therapeutically induced tumour regression. It is implicated in both physiological involution and atrophy of various tissues and organs. It can also be triggered by noxious agents, both in the embryo and adult animal.