Systemic mastocytosis is a disease characterized by an abnormal accumulation of mast cells in skin, bone marrow and viscera. Precise mechanisms of events leading to the migration and proliferation of mast cells in skin is not known. We propose to investigate the in vivo cytokine and chemokine production patterns of human skin in patients with mastocytosis and compare these findings to those of patients with atopic dermatitis and to healthy volunteers, using the suction blister technique. The cytokines/chemokines of interest in this study are stem cell factor (SCF), interleukin (IL)-3, IL-4, IL-6, IL-9, IL-10, TNF-alpha, TGF-beta, MCP-1 and RANTES, all of which have been shown to take part in the proliferation, differentiation or chemotaxis of mast cells. Our hypothesis is that human skin is producing mediators which allow the mast cells to migrate and proliferate in skin, resulting in the clinical picture of urticaria pigmentosa. Suction blisters will be generated in patients, and the cytokine/chemokine contents of the blister fluids will be analyzed by immunoassay. If the chemokine content of the blister fluid is found to be high, chemotaxis of mast cell precursors to the skin may also be examined in vivo by placing a template filled with sterile saline over the blister sites. Punch biopsies will be performed to correlate cytokine levels with mast cell numbers. This study will aid in understanding the pathogenesis of cutaneous mast cell disease and may provide insights into the regulation of mast cell growth and differentiation in tissue-specific microenvironments. It is hoped that these studies will contribute to the design of novel treatment strategies against mast cell associated skin diseases.