الفهرس 
Melanin pigmentary systemOnly 14 pages are availabe for public view
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Abstract
Ultraviolet radiation induces a variety of responses including skin erythema, inflammation hyperpigmentation and xerosis especially, after long-term exposure. Several studies have shown that the ultraviolet radiation directly stimulates melanocyte proliferation and melanogenesis in vitro. However; this response does not explain many skin findings and changes that were reported in skin areas not exposed to UV radiation. These suggest a systemic effect of UV radiation, which may be through release of several cytokines into the circulation, stimulating melanocyte proliferation and melanogenesis. Many studies have suggested this systemic effect of ultraviolet radiation e.g., melanocytes proliferation in hidden skin areas found to be increased under the effect of UVB radiation. Epidermal keratinocytes produce several mitogens that stimulate melanocyte production and melanogenesis, the release of these mitogens was increased when keartinocytes have been irradiated with UV light in vitro. Sera of vitiligo patients treated with PUVA, induced melanocytes and fibroblasts to proliferate in vitro. Increased activity of the deeply situated hair follicle melanocytes in vitiligo skin areas not exposed to PUVA therapy. Presence of DNA photodamage accumulation in the uninvolved skin areas of psoriatic patients undergoing phototherapy. PUVA-induced lentigines in vitiligo patients involved the vitiliginous, as well as the normal appearing skin and the exposed, as well as, the unexposed skin. Punch grafting followed by PUVA therapy resulted in satellite repigmentation that occurred in ungrafted vitiliginous patches at distant sites from the minigrafted areas.
It has been suggested that NB-UVB and PUVA treatments affect several epidermal and dermal cells by the release of several mitogens, melanogens that can reach the circulation and stimulate melanocyte proliferation and melanin production anywhere regardless the irradiated skin area.
In the present study, biopsies from healthy covered skin areas were histopathologically processed assessed for possible significant elevation of melanocytic count and melanin density, by comparing biopsies before exposure and after 1, 3 months of exposure to clarify the skin changes.
This study included 30 UV treated patients, 25 patients have psoriasis and 5 patients have vitiligo. Precautions have been followed to avoid the possible influence of age, sex, skin type and season, the entire study was completed in winter and under standardized conditions for all study subjects.
All patients were subjected to UV radiation; 15 patients to PUVA, 15 patients to NB-UVB according to the clinical protocol followed in the out patient dermatology clinic, Ain Shams University Hospitals. Clinical assessment, digital photography (of some cases) and histopathological assessment were applied at 0 point, 1 and 3 months of treatment.
Statistical analysis of results revealed that no significant difference was found in melanin density by histogram between study groups regarding age and sex. The increase in melanin density by histogram was in skin type V> IV> III at 0 point, 1 and 3 months of treatment, which is mainly due to the higher initial melanin content in darker skin types. The increase in melanin density in psoriatic patients treated with NB-UVB at the time interval 1-3 months is mainly due to that the pathology in psoriasis lacking the autoimmune effectors that circulate freely in plasma affecting the melanocytic number and activity. The increase in melanocytic count although was not parallel with that in melanin density and visual assessment, but can be explained by that the repetitive exposure to UV radiation increases the melanin density, melanocytic activity regardless the number of melanocytes, and that the melanin density correlates well with the visible skin color regardless the melanocytes density.
To conclude, this present work indicates that PUVA and NB-UVB therapies have tanning and hyperpigmention effect on the covered skin areas possibly through an endocrinal mechanism by the circulating melanogens and mitogens, which act on melanocytes not directly exposed to UV radiation. And that both therapies may have similar effect on the covered skin areas.