Keratinocytes in the depigmented epidermis of vitiligo are more vulnerable to trauma (suction) than keratinocytes in the normally pigmented epidermis, resulting in their apoptosis

BACKGROUND: Vitiligo may develop following minor physical trauma. However, in autologous epidermal grafting, depigmentation of the donor (normally pigmented) site from a suction blister is rare, even in cases displaying failure of repigmentation at the recipient (depigmented) site. OBJECTIVES: To examine whether the suction procedure is more likely to damage keratinocytes in the depigmented than in the normally pigmented epidermis of vitiligo, and to determine what kind of damage occurs to the keratinocytes. METHODS: Paired roofs of suction blisters from five patients with generalized vitiligo, five with localized and seven with segmental type, were used for the study. Multiple new lesions developed in two of the five patients with the generalized type. Apoptosis of keratinocytes in the epidermis was determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick end labelling (TUNEL) staining, with immunohistochemistry for Bax and active caspase 3. Expression of Bcl-2, Bax, FLIP and p53, activation of caspases 3, 8 and 9, and cleavage of poly(adenosine diphosphate ribose) polymerase (PARP) in the epidermis were analysed by Western blotting in four patients with each type. RESULTS: Apoptotic keratinocytes, which stained with TUNEL and anti-Bax and antiactive caspase 3 antibodies, were scattered in the blistered epidermis, mainly in the lower portions. The depigmented epidermis displayed significantly more apoptotic keratinocytes than the normally pigmented epidermis. The numerical difference between the paired epidermides was related to the disease activity and not to the type of lesions. The number of apoptotic keratinocytes in the normally pigmented epidermis was as high as that in the depigmented epidermis in the two patients with active generalized type vitiligo. Expression of Bax and p53 in the depigmented epidermis was higher than in the normally pigmented epidermis, whereas expression of FLIP was lower. In addition, the activation of caspases 3, 8 and 9, and cleavage of PARP, were increased in the depigmented compared with the normally pigmented epidermis. The degree of difference in expression and activation was parallel to the results of the TUNEL assay. CONCLUSIONS: The keratinocytes in the depigmented compared with the normally pigmented epidermis of vitiligo may become apoptotic more easily after suction.