Dendritic cell migrations involving the pilosebaceous unit in the development of murine skin

The avian skin in relation to surface ecology

Birds have a layer of plumage over most of the body which provides thermal insulation. The vane-shaped feathers are more efficient than fur in decreasing air movement between the skin microclimate and the ambient environment. Around the feathers is a layer of air, the depth of which for optimum insulation is determined by their angles to the skin surface maintained by the follicular musculature. The mean avian core temperature is 41°C which is higher than in mammals, but skin surface temperature is several degrees lower. Over the exposed skin the microclimate is more variable, but the skin is warmed by the dermal blood vessels and so the feet do not freeze even at sub-zero temperatures. Transpiration occurs through the skin and helps cool the body. Some water vapour is absorbed by the feather keratin, which prevents the feathers from becoming brittle in dry ambient air. Maintenance of the feather vane arrangement requires a more rigid keratin than in hairs. Birds have only one skin gland, the secretion of which contains wax and lipids, but the epidermis is also strongly lipogenic. The sebaceous secretion probably waterproofs the skin, prevents the feathers from becoming too dry, and is anti-microbial. The avian skin surface provides habitats for many commensal micro-organisms and a few bacterial, fungal and arthropod parasites. Pathogenic microorganisms can penetrate the epidermal barrier in wounds or indirectly through the bites of animal parasites. Once in the dermis micro-organisms are combated by immune responses.

Expression of cytoplasmic antigens linked to orthokeratosis during the development of parakeratosis in newborn mouse tail epidermis

An unusual example of two different types of epidermal differentiation occurs side by side in adult mouse tail. The neonate shows only orthokeratotic differentiation, but develops parakeratotic scales in precise patterns over the first two weeks of life, retaining orthokeratotic differentiation at the necks of hair follicles. Certain human IgG antibodies from patients receiving bone marrow transplants bind only to cytoplasmic components of orthokeratotic epithelium. As markers of orthokeratotic differentiation in indirect immunofluorescent studies, these antibodies allowed the timing and location of the change in epidermal differentiation. A specific loss of 'orthokertotic' antigens in the natural switch from orthokeratosis to parakeratosis was demonstrated. The sequence of the orthokeratotic antigens disappearance suggested that the switch to parakeratotic differentiation occurred at a supra-basal level.

Tissue connections in a transplantable virus-producing sebaceous adenoma of the mouse

In this study a transplantable sebaceous adenoma is presented, which maintained its histological structure with similarities to normal sebaceous glands over a long series of transplantations. From the periphery toward the center a basal lamina, an outer layer of undifferenciated stem cells, loosely connected secreting tissue, a tightly packed zone of close cell attachment, and finally a central sebaceous zone can be distinguished. Special reference is made to the belt-like region around the zone of cell lysis and sebum accumulation, which forms a barrier to the surrounding tissue by means of numerous cell adhesions in the form of desmosomes. Relatively few virus particles of the retrovirus group, particularly type A particles, were found in any of the examined tumors.