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M D Kendall

Publications and source records attributed to M D Kendall.

At least 55 records · Page 3Linked to original sources
PubMed1989

Thymic epithelial antibodies: immunohistological analysis and introduction of nomenclature.

During the Workshop "The Thymus. Histophysiology and Dynamics in the Immune System', Rolduc, april 1989, a special workshop was hold to characterize monoclonal antibodies (mAb) to thymic epithelial cells (TEC) in thymus of man, mice, and rat. Twenty-five TEC-specific mAb's were evaluated for their immunohistological staining patterns on reference thymus, thymuses during ontogeny, various other organs (all tissues obtained from the species against the mAb was raised) and thymuses of other species. In this report only immunohistological results of reference thymuses and thymuses of other species are described. Based on the staining patterns on reference thymuses, mAb could be subdivided in 5 main groups. It is proposed to use these clusters of thymic epithelial staining patterns (CTES) to designate individual mAb, awaiting the possible incorporation in existing CD nomenclature for leucocyte differentiation antigens. The present immunohistological approach will be extended by additional analysis for which a protocol was designed. The ultimate goal of this TEC-mAb workshop is to get well-characterized reagents in the analysis of TEC-associated molecules with putative function in intrathymic T-cell processing.

Animals↗
PubMed1989

Histological changes in the thymus during mouse pregnancy.

We studied the cells and microenvironments of the thymus in the pregnant mouse. A morphological and histological study at the light and electron microscope levels shows that the thymus continues to remain active despite massive loss of cortical cells. Many changes are seen in the cortex, but the medulla is relatively unaltered. In very early pregnancy a reduction in cell death and an increase in the numbers of blast cells and mitotic figures indicate a greater activity than in virgin animals. Later in pregnancy, when two-thirds of the cortical cells are lost, there is a continuing presence of mitotic figures and blast cells. Death of thymocytes by apoptosis occurs in associations (rosettes) with macrophages or cortical epithelial cells in the subcapsular and outer cortex. Death of thymocytes with adjacent epithelial cells also occurs in the deep cortex, as it does in virgin females. These results suggest that involution in pregnancy is structurally different from that induced by acute hydrocortisone treatment or other drugs. This supports the view that the term thymic involution describes not one distinct process, but several different processes. The relevance of these findings to the deletion of thymocytes reactive to paternal and fetal antigen is discussed.

Animals↗
PubMed1989

The morphology of perivascular spaces in the thymus.

The perivascular spaces (PVS) are a functional component of the thymus gland that allows cells or possibly soluble products to reach or leave the medulla without the necessity of passing through the cortex. They are connective tissue compartments, continuous with the tissue around the gland, that extend to the cortico-medullary junction where they become merged with the medulla. Around the gland and in their course to the cortico-medullary junction they are delimited by a continuous layer of type-1 epithelial cells (subcapsular/perivascular cells) that rest on a basal lamina. They contain the major blood vessels to and from the medulla, and capillary loops that enter the cortex from the medulla are also ensheathed by the type-1 cells. Capillary loops in the medulla may not be ensheathed. Nerves run in the tunica adventitia of the blood vessels and may also be found separate from the vessels as small unmyelinated fibres that enter the cortex. Lymphatic vessels are formed either in the medulla or at the cortico-medullary junction and leave the gland along the main PVS between thymic lobes. PVS frequently contain lymphocytes, plasma cells and myeloid cells. Lymphocytes free in the connective tissue are commonest at the cortico-medullary junction: macrophages, plasma cells, eosinophils are frequent in the connective tissue of all PVS, and mast cells are closely associated with the veins of PVS and the capsule around the lobes. Some possible functional correlates of this morphological arrangement are discussed.

Animals↗
PubMed1988

Implantation of cultured thymic fragments in congenitally athymic (nude) rats. Ultrastructural characteristics of the developing microenvironment.

Cultured thymic fragments correspond to the thymic microenvironment depleted of lymphocytes and dendritic cells. When these fragments are implanted under the kidney capsule of congenitally athymic rats, lymphocytes and dendritic cells of host origin enter the graft and induce thymus-dependent immunity in the recipient. This paper describes the ultrastructure of the fragments and the changes that occur during the restoration of normal thymic architecture. At the end of the culture period of 6-9 days and in the early stages after implantation, the grafts consist of keratin-containing epithelial cells of unusual morphology that can be labelled with antibodies raised against the epithelium of the mid/deep cortex and the subcapsule/medulla. Normal thymic architecture develops, including nerves and blood vessels, as lymphocytes populate the environment, and by 4-6 weeks the epithelial cells are the same phenotypically and ultrastructurally as those found in normal rat thymus. However, some areas without lymphocytes still contain the atypical epithelial cells seen before implantation. Large multinucleated giant cells are also present with a few associated epithelial cells of subcapsular/medullary phenotype. In conclusion, the cultured thymic fragments contain a hitherto unknown precursor epithelial cell with an atypical ultrastructure and phenotype that is not seen in normal development.

Animals↗
PubMed1988

Elemental levels in mast cell granules differ in sections from normal and diabetic rats: an X-ray microanalysis study.

Mast cells around the thymus of rats stain red with alcian blue and safranin indicating that the mast cells are probably of the peritoneal (connective tissue) type. After the onset of streptozotocin induced diabetes some cells contain both red and blue granules and blue staining cells may appear. X-ray microanalysis of frozen freeze-dried sections from diabetic male CSE Wistar rats showed electron dense granules to have similar amounts of S to normal rat mast cell granules but reduced levels of Na, Mg, P, Cl and K. Two cells also had electron lucent granules with very high levels of Na, Cl, K and Ca and reduced concentrations of S. The differences in elemental composition suggest that the mast cells from diabetic rats are not immature, but are related to the condition of induced diabetes, and that granules of very different composition can occur within a single cell. X-ray microanalysis has given an insight into mast cell granule elemental content which was not possible by conventional biochemical methods.

Animals↗
PubMed1987

Regeneration of the thymus in old male rats treated with a stable analogue of LHRH.

It has been shown that the thymus can be regenerated in intact old rats by implanting s.c. a stable analogue of LHRH. Old male rats were given s.c. implants of osmotic pumps containing a solution in citrate buffer of the analogue which was given at a rate of 1 microgram/h for 28 days. Some animals were given pumps containing buffer alone, and another group of rats was orchidectomized. The animals were killed after 28 days and the tissues weighed and taken for histology. Serum testosterone was measured by radioimmunoassay. Sham-treated rats had small fatty thymuses, which were poorly organized with a very narrow band of cortex. Animals treated with the analogue of LHRH and those which had been orchidectomized had relatively large thymuses which were multi-lobed in drug-treated rats, and atrophied accessory sex organs. The testes were grossly atrophied in analogue-treated rats. Histologically, the thymus looked healthy, having a wide, thymocyte-filled cortex and a clearly defined corticomedullary junction. Serum testosterone concentrations were similar in orchidectomized and analogue-treated rats. It is concluded that it is possible to regenerate the thymus in old rats treated with an analogue of LHRH, but the effect is accompanied by chemical castration. It is also clear that the old pituitary gland is susceptible to the desensitizing action of an LHRH analogue.

Animals↗
PubMed1986

Elemental content of mast cell granules measured by X-ray microanalysis of rat thymic tissue sections.

Mast cell granules were examined by fully quantitative X-ray microanalysis of 20 cells in freeze-dried cryosections. The mast cells were situated mainly in the connective tissue of the thymic capsule of five adult male Carworth Sprague Europe rats. In addition 30 red blood cells were analysed from the same sections. Nineteen of the mast cells had granules rich in S and K. One cell had smaller granules, and in this cell the granules contained high [Ca] and [P] instead of high [S] and [K]. In the majority of cells (13) the S:K ratio was highly correlated and less than 2.2, whereas in the remaining six cells the individual granule ratios were very variable in any one cell and much higher. The mean granule [K] (994 +/- 57 mmol kg-1 dry wt) was about four times the mean cytoplasmic level of 227 +/- 81 mmol kg-1 dry wt. The existence of this difference in concentration between the granules and the cytoplasm suggests that the K in the granules must be bound. The relationship between the [K] and [S] is discussed with regard to the possible binding of heparin and amines in the granules.

Animals↗
PubMed1986

Reappearance of the thymus in old rats after orchidectomy: inhibition of regeneration by testosterone.

The thymus is a critically important organ during development, but atrophies progressively during the ageing process after puberty and is often considered to be unimportant in adult life. We have found that the thymus, which is grossly atrophied in 12- to 15-month-old male rats, is markedly restored in size 30 days after orchidectomy. The organ then appears normal histologically, having a well-defined cortex and medulla, is vascularized and filled with thymocytes. The regeneration of the thymus after orchidectomy was inhibited in a dose-related fashion by testosterone implants which produced serum concentrations of testosterone within the physiological range. The thymus was also increased in size after orchidectomy of 10-week-old rats, and testosterone inhibited the enlargement of the thymus. These results have important implications for the possible enhancement of the immune system with associated improvement of health during ageing and disease. They also point to an important physiological link between the endocrine and immune systems.

Animals↗
PubMed1986

The syncytial nature of epithelial cells in the thymic cortex.

The epithelial cells of the cortex of human and rodent thymus glands were examined by light and electron microscopy, and the intracellular membrane potentials measured from the subcapsular, cortical and medullary regions. In the human thymus cortex, there is a highly correlated age-independent relationship (r = 0.78) between the distance in micron from one adjacent Type 2/3 epithelial nucleus to another, and the number of thymocytes between them. In rodent glands that had undergone some degree of involution due to hypoxia simulating an altitude of 17 000 feet or following the injection of phenylhydrazine, Type 2/3 epithelial cells were often found to be bi- or multinucleated. Electrophysiological studies of 10 mouse thymus lobes using 0.2 micron tipped electrodes showed that there were highly significant differences (P less than 0.0001) between the intracellular membrane potentials of the subcapsular zone, the cortex and the medulla. When dyes were injected intracellularly (through 0.5 micron tipped electrodes) into individual epithelial cells, methylene blue remained within the cytoplasm, but procion yellow passed in 30 minutes into the nuclei of all the epithelial cells of the cortex but not those of the subcapsular zone, nor the medulla. This indicates that the cortex must be a functional syncytium and it differs in this respect from the rest of the gland.

Adolescent↗
PubMed1986

Elemental concentrations within types 2 and 3 epithelial cells of the rat thymus.

The elemental composition (Na, Mg, P, S, Cl, K, Fe and Zn) of epithelial cells of rat thymus cortex has been determined using X-ray microanalysis of freeze-dried frozen sections. The cytoplasm contained highly significantly lower levels of potassium and phosphorus than the nuclei. When the results were compared with a previous study of the elemental levels in cortical thymocytes (using the same material), only differences in the P concentration were found. This is probably attributable to the greater degree of leptochromasia usually observed in epithelial cells compared with thymocytes. Since thymocyte maturation depends very closely on the microenvironment created by the epithelial cells, the great similarity in elemental levels observed in this study could be important in the control of cell division and maturation events.

Animals↗
PubMed1985

Atrophy of the thymus in rats rendered diabetic by streptozotocin.

The thymus atrophied rapidly in rats rendered diabetic by a single injection of streptozotocin. The weight of the gland was reduced to one-fifth of its original weight within three weeks. Histologically there was a great loss of cortical thymocytes and a marked increase in mast cells lying in the thickened fibrous tissue. These findings may have a bearing on the state of immune deficiency observed in animals with diabetes induced by streptozotocin.

Animals↗
PubMed1985

Reappearance of thymus of ageing rats after orchidectomy.

There was no visible thymus in ageing rats of 18 months, and 7 days after orchidectomy there was still no evidence of a thymus. By 30 days after the operation, however, there was a well-defined and well developed bilobular thymus overlying the heart, although it was smaller than those observed in 10-week-old rats. Histologically, the tissue appeared normal, was well vascularized, filled with lymphocytes and several mitotic figures were also seen. When compared with sham-operated animals, blood from these animals had a significantly higher lymphocyte count. These results have important implications for the possible enhancement of the immune system with associated improvement of health during ageing.

Aging↗
PubMed1985

The ultrastructure of the epithelium of the ductuli efferentes testis in the common starling (Sturnus vulgaris).

The ductuli efferentes of male common starlings (Sturnus vulgaris) were prepared for light and electron microscopy. The epithelium of breeding birds was pseudostratified, consisting of ciliated cells, which were of the same type throughout the ductules, and of two types of non-ciliated cells: an electron-dense form with complex lateral invaginations, long microvilli and apical invaginations found in proximal ductuli efferentes (Type 1 a) and a less dense, taller, seemingly more secretory cell found distally (Type 1 b). Both types contained crystal-like structures in granular and transitional endoplasmic reticulum, which were occasionally seen in ciliated cells and not elsewhere. These 'intracisternal bodies' were probably proteinaceous in nature. The ciliated cells were typically more electron-lucent than the non-ciliated cells. They adopted the height and interdigitation characteristics of the surrounding epithelium. Occasional annulate lamellae were encountered. Intraepithelial lymphocytes were seen occasionally, notably in non-breeding birds. The epithelial morphology of the non-breeding common starling is briefly mentioned. The tubules were collapsed and apparently inactive, although signs of proliferative activity were seen in birds killed in February. The distinction of the epithelial cells into one ciliated and two non-ciliated types in this study is discussed in the light of previous work, as differences were found to exist. It is suggested that care should be taken in the use of mammalian tubule nomenclature when it is applied to birds.

Animals↗
PubMed1985

The morphology of the haemopoietic cells of the yolk sac in mice with particular reference to nucleolar changes.

Nucleolar changes of haemopoietic cells during the development of the mouse yolk sac blood islands were qualitatively examined by light and electron microscopy. Haemopoiesis in the yolk sac begins at seven days of gestation and, after the formation of vitelline vessels, erythropoiesis appears to be active at ten days. At 7-8 days of gestation, angioblasts have large and reticulated nucleoli in connection with the nuclear envelope either through the invagination of the nuclear membrane, i.e. canals and tubular or lamellar structures, or directly. The nucleoli of the fixed primitive erythroblasts at 8-9 days are of compound type and invaginations of the nuclear membrane are rarely seen. In free erythroblasts, fibrillary areas become obscure. In matured erythroblasts, remnants of the nucleoli are present in the heterochromatin masses. Nucleolar changes in each stage are so characteristic that nucleolar structure can be useful in the recognition of the differentiation stages of yolk sac haemopoetic cells.

Animals↗