الفهرس 
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Abstract
Hair has a great social significance for human beings. Human hair growth activity reflects both physiological and pathological conditions.
Alopecia is one of the most important hair disorders and can be viewed as disorders of adult stem cells.
The field of epithelial stem cells is progressing rapidly largely because of technical advances in molecular and cellular biology.
Many recent studies were done to assess the role for stem cell activity in alopecia. Stem cells in the follicles may develop differently depending on location. Stem cells localized in the bulge of hair follicles are thought to be involved in the cyclical regeneration of hair follicles.
Hair follicle stem cells possess stem cell characteristics, including multipotency, high proliferative potential, and ability to enter quiescence.
Lineage analysis has demonstrated that all epithelial layers within the adult follicle and hair originated from bulge cells.
CK17 and CK19 are stem cell markers that are found in the hair follicles and may play a role in the aetiopathogenesis of alopecia.
CK17 protein is present in the outer root sheath and the matrix of the bulb but otherwise persists in a detectable form only in the medulla of the differentiated hair shaft. K17 null mice exhibit severe alopecia in an age- and strain-dependent fashion.
CK19 is a marker for putative stem cell-containing epithelial compartments, in order to characterize stem cell distribution in the human hair follicle throughout the hair cycle. CK19-reactive cells were found either continuously or at intervals in the outermost cell layer of the outer root sheath while a small number of CK19-positive cells were sporadically found in the inner cell layer of the outer root sheath of terminal hair follicles of the scalp.
In our study, we investigated the expression of stem cell markers(cytokeratin 17 and cytokeratin 19) in scarring and non- scarring alopecia.
This study included 30 patients with alopecia (15 with non-scarring alopecia and 15 with scarring alopecia) and 10 apparently healthy individuals as control. The patients were selected from the outpatient clinic of Dermatology Department, Minoufia University Hospital.
Punch biopsy was taken from the lesional skin of alopecia in patients and from the scalp of the controls. Three sections were formed from each block. One section was stained by Haematoxyline and Eosin and the other two sections were stained with immunohistochemical stain for detection of cytokeratin 17 and cytokeratin 19.
We found that on comparing the non-scarring group with the control group, there was a statistically significant difference between them as regarding to the presence of CK17 in the outer layers of the hair
follicles and in sebaceous glands. Also, there was a statistically significant difference between them as regarding to the presence of CK19 only in the inner layers of the hair follicles.
On comparing the scarring group with the control group, there was a statistically significant difference between them as regarding to the presence of CK17 in the outer layers and the inner layers of the hair follicles and in sebaceous glands but regarding CK19, there was no statistically significant difference between both groups.