Regulation of epidermal proliferation and differentiation in psoriasis

Three decades of psoriasis research: where has it led us?

Psoriasis is a common chronic skin disease. Its pathogenesis has intensively been investigated in the last 3 decades. In the 1970s, the observed increased proliferation of keratinocytes and their altered differentiation were considered to be the most important signs and causes of psoriatic skin lesions. Since the early 1980s, T cells slid into the focus of psoriasis research. It was then postulated that a subpopulation of T cells, so-called T1 cells, and their prominent cytokine interferon-gamma, had a dominant role in the pathogenesis of psoriasis. In the last decade, new data regarding macrophages and dendritic cells and the high therapeutic success of anti-tumor necrosis factor alpha biologics led to the assumption that antigen-presenting cells are important not only in the induction of psoriasis but also in its maintenance. The knowledge gained over the past 3 decades let us postulate that psoriasis is an immunologically induced, overshot, regeneration-like reaction of the skin in which various cells play a dominant role at different stages. This hypothesis is also supported by the very recent discoveries about interleukin (IL)-22, IL-20, and IL-23.

Effects of trypsin on the cyclic AMP system of the pig skin

Trypsin increased cyclic AMP levels of the pig skin. This effect was markedly potentiated by the cyclic nucleotide phosphodiesterase inhibitor theophylline. Without theophylline this trypsin-induced cyclic AMP accumulation was transient and the maximal accumulation was noted by 5 min. Soybean trypsin inhibitor inhibited this trypsin-induced cyclic AMP accumulation. After the trypsin treatment, marked acantholysis was noted histologically and the decreased responsiveness to other adenylate cyclase stimulators was seen. The decrease of the epinephrine response was most marked and that of histamine response was much less. Both low and high Km cyclic nucleotide phosphodiesterase activities were decreased by the trypsin treatment. However, at 5 min incubation time, when the increase in cyclic AMp level was most marked, the decrease in the phosphodiesterase activities was minimal. Trypsin seems to reveal its action through the proteolytic activation of adenylate cyclase system of the skin.