The dermoepidermal junction in psoriatic skin as revealed by scanning electron microscopy.

Our previous ultrastructural and immunohistochemical studies, in vivo and in vitro, have shown important modifications of the basement membrane of psoriatic skin, which could play a key role in the alterations of keratinocyte adhesion, migration, proliferation and differentiation. In order to complete the morphological examination of all the structures in the dermoepidermal junction of psoriatic skin, we carried out a scanning electron microscopic study using biopsies taken from eight psoriatic patients. The biopsies were fixed in a mixture of 0.2% paraformaldehyde and 0.25% glutaraldehyde in 0.1 M cacodylate buffer at pH 7.4. The specimens were then frozen in liquid nitrogen and fractured following the natural cleavage planes and observed under a Jeol JSM-6301F field emission scanning electron microscope operating at 1.8-2.0 kV. The basal keratinocytes observed showed pore-like depressions on the lateral plasmalemma and villous-like projections in very dilated intercellular spaces. Moreover the basal cell plasma membrane was seen to rest on the papillary dermis without interposition of the lamina densa. The detachment of some keratinocytes enabled the examination of the lamina densa, which appeared slightly granular with numerous focal interruptions through which it was possible to observe the underlying collagen fibres. These findings, together with previously reported findings, support the hypothesis that in psoriasis molecular and structural alterations of the dermoepidermal junction are present, that could fundamentally alter the regulation of the cytomorphological processes and the normal functions of the basement membrane.