HUMAN MAST-CELLS ACTIVATE FIBROBLASTS - TRYPTASE IS A FIBROGENIC FACTOR STIMULATING COLLAGEN MESSENGER-RIBONUCLEIC-ACID SYNTHESIS AND FIBROBLAST CHEMOTAXIS

The effect of human mast cells on fibroblast activity was studied usin g an organotypic skin-equivalent culture system. Human mast cell-1 (HM C-1) cells were embedded in a collagen gel with neonatal dermal fibrob lasts at a ratio of 1:4; keratinocytes then were allowed to stratify a bove this composite culture. Analysis of type a1 (I) procollagen mRNA synthesis by in situ hybridization revealed a substantial increase in mRNA levels in the presence of mast cells and especially following deg ranulation, induced by calcium ionophore A23187. Tryptase, a major pro duct of human mast cells, could substitute for mast cells in this cult ure system, up-regulating procollagen mRNA synthesis, Tryptase pretrea ted with the specific protease inhibitor bis(5-amidino-2-benzimidazo-l yl)methane (BABIM) markedly attenuated the collagen mRNA up-regulation , Further studies revealed HMC-1 cell sonicates stimulated fibroblast chemotaxis and procollagen mRNA synthesis. Inhibition of HMC-1 sonicat es with either BABIM or a neutralizing mAb against tryptase resulted i n significant reduction of fibroblast chemotaxis and procollagen mRNA, implying that tryptase accounted for the majority of HMC-1 sonicate a ctivity. Tryptase directly stimulated fibroblast chemotaxis with optim al concentrations between 10 pM and 1 nM. The maximal response of opti mal concentrations of tryptase was comparable with the known fibrogeni c factor, TGF-beta. Inhibition of tryptase with BABIM resulted in simi lar to 50% reduction in chemotactic activity. Additional studies revea led that tryptase (0.3-3 nM) stimulated procollagen mRNA synthesis in confluent monolayers of dermal fibroblasts.