Adhesion of human mast cells to extracellular matrix provides a co-stimulatory signal for cytokine production

Engagement of integrin receptors during cell adhesion leads to changes in t he morphology and the state of activation of cells. We therefore examined w hether mast cell adhesion to extracellular matrix proteins affects the synt hesis and release of various proinflammatory cytokines. Cells of the human mast cell line HMC-1 were added to fibronectin (FN)-, vitronectin (VN)- or, as a control, bovine serum albumin (BSA)-coated wells and were stimulated with phorbol 12-myristate 13-acetate (PMA) and/or calcium ionophore A23187 (ionophore). Cytokine production was evaluated using semiquantitative rever se transcription-polymerase chain reaction (RT-PCR) analysis of cell extrac ts and enzyme-linked immunosorbent assay (ELISA) analysis of cell supernata nts. After a 4-hr incubation, mRNA expression of interleukin (IL)-8 (and we akly of IL-6) was up-regulated in matrix-adherent cells, with further incre ase in the presence of PMA and/or ionophore, compared with unstimulated cel ls. High-level de novo expression of IL-3 and of granulocyte-macrophage col ony-stimulating factor (GM-CSF) was observed mainly in matrix-adherent cell s. These changes were paralleled by the secretory pattern of HMC-1 cells af ter a 24-hr stimulation. Unstimulated cells adherent to FN or VN had alread y released small amounts of IL-8, and both VN- and FN-adherent cells produc ed, almost invariably, a higher level of cytokines than BSA-exposed cells a fter additional stimulation. These results show that mast cell adhesion to matrix proteins by itself has only selected and minor effects, but addition al activation of mast cells by secretory stimuli causes significantly enhan ced cytokine gene expression and secretion, suggesting that mast cells are far more active in their natural tissue environment than hitherto suggested from data in suspension cultures.