Clinical and E.xperimentai Allergy. 1991, Volume 21. pages 711-714 Tumour necrosis factor stimulates human skin mast cells to release histamine and tryptase F. J. VAN OVERVELD, Ph. G. JORENS, M. RAMPART*, W. DE BACKER P. A. VERMEIRE Departments of Respiratory Medicine and * Pharmacology, University of Antwerp (UIA). Belgium Summary Besides its effects on tumour cells, tumour necrosis factor (TNF) also acts on a variety of other cells, thus enhancing inflammatory and immune processes. In view of the prominent role ofthe mast eel! in such processes, tbe aim ofthe present study was to assess the effects of reeombinant TNF-a on human mast cells. Mast cells from the infant foreskin obtained during circumcision were dispersed by an enzymatic technique using collagenasc and hyaluronidase. Cells thus obtained were pooled, washed and separated by Percoll gradient cenlrifugalion. Mast cells, with a purity of 70 90% were incubaled for 60 min with 1 0 " to 10 •^ M rTNF-a. Histamine and tryptase levels were assessed in the cell supernatant by spectrofluorometry and radioimmunoassay (RIA) respectively. A concentration dependent release of histamine was observed, which reached a maximum of 11-5 + 2-2 nmol/IO*" cells at 10"** M rTNF. Release of tryptase was also concentration dependent and reached a maximum of 293+105 mU/IO'' cells {10 " rTNF). rTNF-oc thus appears lo be a direct stimulus for mast cells to degranulale and to release both histamine and tryptase. Clinical and Experimental Allergy, Vol. 21, pp. 711 -714. Submitted 22 March 1991; revised 1 July 1991; accepted II July 1991. Introduction During the past decade the list of poiypeptides (cytokines) regulating the action of immune-, inflammatory- and haematopoietic cells has grown rapidly. One of these cytokines, TNF-a, is primarily produced and secreted by activated macrophages, but also T-lymphocytes. natural killer cells and mast cells can be induced to secrete it [1,2]. Induction of TNF production was observed after admin- istration of various agents such as endotoxin, interferon--/ (iFN-7). and colony stimulating factors (CSF) [3]. Besides acting on tumour cells, TNF activates neutrophils, stimu- lating their adhesion to endothelial cell surfaces and enhancing their phagocytic activity [4]. Furthermore. TNF stimulates the production of several cytokines such as interleukin-l (TL-I). IL-6, IFN-/^1 and GM-CSF. as well as cytokine receptors [3]. It was shown that IL-1 or iTNF-a in combination with reeombinant GM-CSF enhanced histamine synthesis in haematopoietic cells [5]. Correspondence: Dr F. J. van Overveld. Deparlnicnl ot" Respiralory Medicine. Universily of Antwerp (UIA), Universiteilsplein I. B-2610 Aiiiwcrp. Belgium. In view ofthe association of high serum levels of TNF with poor prognosis in sepsis, graft versus host disease, acute respiratory distress syndrome and its role in many other immunological processes this factor was found to be an important mediator of general inflammalion [6], Mast cells are classically known to be involved in immediate hypersensitivity and allergic types of pro- cesses. On the basis of the increased numbers found in both acute and chronic inflammatory condiliuns, mast cells are also thought to have an effect in many different inflammatory events [7]. Yel ihe precise role ofmast cells in inflammation is uncertain. Whereas many niasl cell- derived mediators clearly can have pro-inflammatory efTects. products of mast cell activation may also function to limit inflammation. During mast cell degranulation tryptase is exocytosed with other preformed mediators, including histamine. Because it is essentially unique to mast cells, Irypiase is a more specific marker of mast cell activation than hisia- mine. Since tryptase has been shown lo generate active C3a from complement C 3 and lo destroy high molecular weight kininogen and fibrinogen. iis release may suggest participation in inflammatory processes [8]. 71