Self-sustaining pathological processes in skin psoriasis.

Clinical findings suggest that an etiological factor of skin psoriasis (SPs) is of nervous origin. Vasoactive intestinal peptide (VIP) is the most probable candidate for such a factor since VIP is the only neurotransmitter the extracellular level of which increases during SPs exacerbation and decreases in remission. VIP released from skin nerves induces keratinocyte hyperproliferation, angiogenesis, vasodilation, and other SPs-associated cutaneous pathological processes. These can go on over a prolonged period since (1) once released, VIP induces its own further secretion; (2) VIP induces release of interleukin-6 (IL6) that evokes both its own further release and release of VIP. Thereby, a vicious circle-type mechanism perpetuating and amplifying VIP secretion can function in the focuses of psoriatic damage. The mechanism described operates still more intensively under the effects of parathyroid hormone, aldosterone, and enkephalin, the blood levels of which are elevated in patients with SPs. The above explains such features of SPs as its association with human immunodeficiency virus infection, mental stress, alcohol consumption, smoking, and dependence of SPs on skin pigmentation.