Inflammatory and immune reactions associated with stratum corneum and neutrophils in sterile pustular dermatoses

In this review we present our own experimental findings as well as those from the literature related to the pathomechanisms for the inflammatory changes in psoriasis and its related diseases. A growing body of evidence has indicated that T cell-mediated immunity plays an important role in triggering and maintenance of psoriatic lesions. It has been revealed that lymphokines produced by activated T cells in psoriatic lesions have a strong influence on the proliferation of the epidermis. Characteristic neutrophil accumulation under the stratum corneum can be observed in the highly inflamed areas of psoriatic lesions. These neutrophils are chemotactically attracted and activated there by synergistic action of chemokines, IL-8 and Gro-alpha released by stimulated keratinocytes, and particularly by C5a/C5a des arg produced via the alternative complement pathway activation. We demonstrated that the infiltrating neutrophils adhere to iC3b-opsonized corneocytes to produce active oxygen and probably lysosomal enzymes. From a close relationship observed between neutrophil accumulation and high mitotic ratio of the lesional epidermis, we think that these stimulated neutrophils influence the growth and differentiation of epidermal keratinocytes. Aberrant expression of HLA-DR on neutrophils suggests their activation of infiltrating T cells in the presence of bacterial superantigen. These T cells in turn influence the transepidermal neutrophil migration through the effect of their cytokines on the keratinocyte production of proinflammatory mediators including IL-8 and C3. In this review we discuss the pivotal roles played by stratum corneum and neutrophils in several skin diseases, where neutrophils accumulate beneath the stratum corneum in a sterile condition.