PubMed · 6357028
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G Illy, P El Baze, J P Ortonne. 1983. [Merkel's cell : current data].. https://pubmed.ncbi.nlm.nih.gov/6357028/
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The density and distribution of Merkel cells in human embryonic and fetal skin were studied using an immunolabeling technique on epidermal and dermal sheets obtained by ethylenediamine tetraacetic acid separation. Merkel cells were identified by the known cytokeratin markers CK20 and CK18. Merkel cells showed CK20 immunoreactivity as early as 56 d estimated gestational age (EGA) in the palmar epidermis (133.11 +/- 44.27 cells/mm2). The density increased rapidly, reaching a maximum of more than 1400 cells/mm2 at 80-90 d EGA. At this stage, the cells became distributed along the primary epidermal ridges. In the palmar epidermis of fetuses older than 100 d EGA, the distribution of Merkel cells showed the same pattern, but the density then decreased gradually. Merkel cells were not observed in ductal and glandular portions of eccrine sweat glands. In the epidermal sheets of hairy skin, a few cells were first seen in the fetus at 75 d EGA. At 100 d EGA, only a few Merkel cells were observed, mostly in the hair pegs and bulbous hair pegs. In the older fetus, ring-like arrangements and aggregates of Merkel cells were prominent in the infundibulum and bulge of hair follicles, respectively. Merkel cells were both globular and dendritic in shape. The ratio of dendritic to globular cells increased gradually until the period of highest Merkel cell density in both the glabrous and hairy skin. All Merkel cells located in the dermis were globular in shape. In accord with the results obtained, we postulate that Merkel cells may have some functional role in the formation and proliferation of eccrine sweat glands and hair follicle anlagen in developing skin.
The mixed epidermal cell lymphocyte reaction (MECLR) is a commonly used method to study the effects of ultraviolet B (UVB) radiation on the skin immune system. In UVB experiments dosimetry is very important. The influence of irradiance on the MECLR was studied in vitro using Philips FS40 lamps with variable UV intensities. Irradiation of isolated epidermal cells with high irradiance impaired the alloactivating capacity more than irradiation with low irradiance. In vivo, the influence of long-term UVB exposure on the MECLR was studied by treating normal healthy volunteers with suberythemagenic doses of UVB thrice weekly during 4 weeks. The first set of experiments, using low irradiance Sylvania UV-21 F75/85 W lamps, resulted in a decrease of MECLR responses of 83.1%. In the second set of experiments performed a year later, employing an identical protocol except for the use of high irradiance Waldmann UV-21 F85/100 W lamps, an increase of MECLR responses of 99.7% was observed. Volunteers of both sets of experiments received equal doses of UVB. In conclusion, this study shows that in vitro UVB-induced suppression of the MECLR is critically dependent on irradiance and therefore might explain contradictory results described in the literature. The in vivo data suggest that, comparable to the in vitro experiments, irradiance may influence the effects of UVB irradiation in vivo. Further experiments should prove whether this is indeed the case.
The skin barrier primarily protects the body against uncontrolled loss of water and in addition prevents water and matter of the environment from indiscriminately entering the living system. The current concept of the skin barrier suggests that permeability is governed by a hydrophilic and a hydrophobic "channel". To account both for the barrier function and the hydrophilic and hydrophobic pathways through this barrier, we propose a new model, "the domain mosaic model of the skin barrier", which depicts the bulk of the lipids as segregated into crystalline/gel domains bordered by "grain borders" where lipids are in the fluid crystalline state. Such an arrangement provides for an effective "water-tight" barrier that allows a minute and controlled loss of water to keep the corneocytes moistened. In addition the model provides for the necessary mechanical properties permitting bending and stress imposed on the skin surface. Furthermore, the fluid character of the "grain borders" represents areas where lipid and hydrophobic molecules may diffuse through the system on down-hill gradients. It is suggested that in the border areas between the crystalline domains, structural transformations of the lipid organization due to permeation promoters may take place without structural changes in the bulk organization of lipids in the crystalline or gel phase.