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R K Jordan

Publications and source records attributed to R K Jordan.

26 records · Page 2Linked to original sources
PubMed1976

Development of sheep thymus in relation to in utero thymectomy experiments.

The developing thymus of sheep embryos has been examined from 20 days of gestation onwards. The initial relationships of the thymus to the parathyroid III and the pericardium are maintained so that the thymus develops as an extensive and complex structure consisting of paired cords of tissues on either side of the neck continuous with a single, fused structure in the anterior mediastinum. Histological examination of the developing thymus revealed that thymic lymphopoiesis commences at 36 days of gestation (term = 150 days). The results indicate that conclusions drawn from sheep thymectomy, usually performed after 60 days of gestation, must be interpreted with caution.

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PubMed1975

The development of the thymus in the nude mouse.

The developing thymus of nude mouse embryos (derived from homozygous, nu/nu x nu/nu, matings) has been examined from 13 days' gestation onwards for the presence of large basophilic stem cells or their lymphoid progeny. No trace of either stem cells or lymphocytes has been found at any stage, indicating that from the earliest stages of thymic development lymphopoiesis is defective. However, histological evidence alone is not sufficient to rule out the possibility that small numbers of lymphocytes may be present in the nude thymus. Recent evidence that nude mice born of heterozygous (nu/+) females possess some T lymphocytes and "T lineage" cells is discussed in relation to these findings. A series of morphological changes have been defined within the epithelial component of the developing nude thymus, further analysis of which may help to determine the nature of the thymic defect.

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PubMed1975

An electron microscopic study of the histogenesis of the parathyroid gland in the sheep.

Definitive chief cells, characterized by the presence of specific secretory granules and typical membrane configurations, were present in the developing parathyroid glands of sheep embryos from 26 days of gestation (term = 150 days). During earlier stages of gestation developing chief cells contained lysosomal systems which appeared to be concerned with the autophagy of retained secretion product. The EM evidence suggests that physiologic release of the hormone does not occur until at least 30 days of gestation, which correlates well with the experimentally established time of onset of functional capacity in the parathyroid gland in the sheep. 'Bark cells' were found in the parathyroid primordia of embryos between 20 and 27 days of gestation. The significance of these "dark cells" is discussed with respect to glutaraldehyde fixation and to their possible relationship to chief cells.

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PubMedDate not supplied

Thymic epithelium and the induction of transplantation tolerance in nude mice.

Immunological tolerance of self has been studied experimentally by the induction of unresponsiveness to antigens of the major histocompatibility complex (MHC) in neonatal mice. The specific unresponsiveness resulting from such neonatal tolerance induction is first demonstrable in the thymus, suggesting that neonatal tolerance is induced by some cellular component of the thymus, or at some prethymic stage. Recent transplantation studies suggest that thymic epithelium, derived by organ culturing fetal mouse thymus in the presence of deoxyguanosine, survives in an allogeneic host environment despite the continued expression of MHC donor antigens, but fails to induce allotolerance. We demonstrate here that embryonic thymus lobes organ cultured at 24 degrees C, a treatment that deletes the lymphohaematopoietic component of thymus leaving the epithelial matrix intact, when transplanted to intact histoincompatible recipients, similarly survive for a prolonged period and do not induce tolerance to donor MHC antigens. However, when such culture-derived thymic epithelium is allografted to athymic nude mice, host-derived lymphocytes from both the epithelial graft and recipient spleen are unresponsive to the MHC antigens of the epithelial donor. The results suggest that, when investigated in a system which precludes the possible involvement of extrinsic mature T cells, processed by the syngeneic host thymus, thymic epithelium may induce transplantation tolerance.

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PubMedDate not supplied

In vitro studies on the ontogeny of lymphocyte populations.

We have investigated the ontogency of lymphocyte populations in the mouse embryo using organ culture techniques. Our results indicate that B lymphocytes are generated independently in foetal liver, foetal spleen and foetal bone marrow, while T lymphocytes are generated in thymus. We have characterised the structural and functional properties of developing lymphocytes in the organs. Our results suggest that foetal lymphocytes may differ from adult lymphocytes in a number of important respects which may have a bearing on the generation of tolerance to self antigens.

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