Background:  Psoriasis vulgaris is a common chronic inflammatory dermatosis. Disorders in keratinocyte proliferation, differentiation, inflammation and immune dysregulation are the major factors implicated in the pathogenesis of psoriasis vulgaris.

Methods:  The study was performed in skin specimens of 25 patients with psoriasis vulgaris and a control group of 10 individuals without a skin disease. Biopsy specimens from lesional and normal skin were analyzed by immunohistochemical method for expressions of Ki-67, Bcl-2, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL), tumor necrosis factor alpha (TNF-α) and nuclear factor kappa B (NF-κB). In addition, densities of mast cell infiltration were also investigated.

Results:  Ki-67 and TUNEL indexes and TNF-α and NF-κB expressions were significantly higher in psoriatic epidermis than in normal epidermis (p < 0.05). There was no significant difference at Bcl-2 reactivity between the normal and the psoriatic epidermis (p > 0.05); however, Bcl-2 staining intensity of lymphocytes was higher in psoriatic lesions than in normal dermis (p < 0.05). Additionally, the number of mast cells was significantly higher in psoriatic dermis than in normal skin (p < 0.05).

Conclusions:  There were several complex factors involved in the pathogenesis of psoriasis. We conclude that cellular damage and apoptosis temporarily coincide with epidermal proliferation during the course of psoriatic hyperplasia.