Biomedical subjects
Publications and source records attributed to A E Wild.
By means of an erythrocyte-antibody rosette technique, Fc receptors, functional at pH 6.0 but not at 7.2, were shown to be present on enterocytes isolated from duodenum and jejunum (but absent from ileum) of 12-20-day-old suckling rats.
In Xenopus laevis tadpoles, wounding of the outer cornea failed to initiate lens regeneration. If both the outer and inner corneas were wounded or if the lens was dislocated, lens regeneration was initiated but failed to continue beyond stage III. However, lensectomy followed by re-implantation of the lens resulted in the regeneration of a fully differentiated lens in several cases, despite the presence of the re-implanted lens. Although some of the regenerates in these eyes were also arrested at stage III, those which attained full lens differentiation, i.e. stage V, developed normally and synthesized crystalline from the onset of stage IV as indicated by a positive immunofluorescence reaction. Histological examination of the dislocated and re-implanted lenses showed the majority of them to be normal in appearance. Cornea transplanted to the posterior chamber of the eye also regenerated a lens in the presence of the re-implanted lens. All these regenerates underwent lens fibre differentiation to give stage-V regenerates. These findings show that lens regeneration from the cornea can occur in the presence of lens. Results are discussed on the basis that contrary to earlier suggestions, an inhibitory lens factor does not exist in vivo, but rather that a factor for the initiation and maintenance of regeneration emanates from the eye cup and upon wounding of the inner cornea is able to reach the inner cell layer of the outer cornea and initiate lens regeneration.
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Rabbit yolk sac splanchnopleur exposed in utero to IgG-HRP and IgG-ferritin conjugates, rabbit and bovine anti-HRP antibodies, free HRP, ferritin and human IgG, was examined ultrastructurally in an attempt to determine whether or not coated micropinocytotic vesicles are involved in selectively transporting immunoglobulins across yolk sac endodermal cells. Human, rabbit and bovine IgG-HRP conjugates, rabbit anti-HRP antibodies, free HRP and human IgG, all become localised in coated micropinocytotic vesicles. Differences were observed in that only human IgG and rabbit anti-HRP antibodies could be located in the intercellular space and bovine IgG-HRP conjugate could not be detected in coated micropinocytotic vesicles in confluence with the lateral and basal plasmalemma. Bovine anti-HRP anti-bodies, IgG-ferritin conjugates, and free ferritin, could not be observed in coated micropinocytotic vesicles. All proteins were detected in macropinocytotic vesicles, and dense bodies resembling phagolysosomes. Results are discussed in the light of a proposal that selection occurs at the cell surface during formation of coated micropinocytotic vesicles and is not linked to intracellular proteolysis.
The transport of immunoglobulins from mother to foetus and newly born mammal involves selective events which are independent of molecular size, related to immunoglobulin class, structure, and species of origin, and involve considerable protein degradation. Such events are briefly described as background information to a discussion of how selection of proteins might take place during transport across the cellular barriers concerned, namely the yolk sac splanchnopleur, chorio-allantoic placenta, and small intesting. Until recently the Brambell hypothesis has been the most favoured explanation. This implies that selection occurs intracellularly, within endodermal cells of the yolk sac splanchnopleur and small intestine, and within the syncytiotrophoblast of the chorio-allantoic placenta, of certain species. It also suggests that specific receptors are present which give attached proteins protection from degradation when the vesicles containing them fuse with lysosomes; such protected proteins are then liberated from the vesicle by exocytosis. This hypothesis is examined in the light of what is now known about the mechanism of uptake and transport of proteins by the endodermal cells and syncytiotrophoblast. It is suggested that rather than being an intracellular event, involving protection from proteolytic degradation, selection takes place at the cell surface. Evidence is presented, some direct and some circumstantial, that proteins may be selectively endocytosed by coated micropinocytotic vesicles, and non-selectively endocytosed through a complex apical canalicular system leading to macropinocytotic vesicle formation. In the small intesting of the suckling rat these two processes appear to be segregated, selective uptake occurring in the proximal half and non-selective uptake occurring in the distal half. In the endodermal cells of the rabbit yolk sac splanchnopleur, and by implication in the syncytiotrophoblast of man and monkey, it is suggested that both selective, and non-selective, uptake of protein occurs. Non-selective uptake into macropinocytotic vesicles is regarded as an event leading to complete degradation of all contained protein and functioning so as to supply the foetus and newly born mammal with essential amino acids. Selective uptake into coated micropinocytotic vesicles is regarded as an event leading to the transport of immunoglobulins across the cell without any contact with lysosomes, and functioning so as to supply the newly born mammal with protection against invasive organism. Specific receptors are still required but only for the initial uptake and segregation of proteins into coated micropinocytotic vesicles. The role which the glycocalyx might have in such selective binding of proteins is considered and possible difficulties in characterization of specific receptors brought to light in view of the likely overwhelming need for non-specific binding to effect non-selective uptake.