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 the morphology and the state of activation of cells. We therefore examined whether mast cell adhesion to extracellular matrix proteins affects the synthesis 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 reverse transcription–polymerase chain reaction (RT–PCR) analysis of cell extracts and enzyme-linked immunosorbent assay (ELISA) analysis of cell supernatants. After a 4-hr incubation, mRNA expression of interleukin (IL)-8 (and weakly of IL-6) was up-regulated in matrix-adherent cells, with further increase in the presence of PMA and/or ionophore, compared with unstimulated cells. High-level de novo expression of IL-3 and of granulocyte–macrophage colony-stimulating factor (GM-CSF) was observed mainly in matrix-adherent cells. These changes were paralleled by the secretory pattern of HMC-1 cells after a 24-hr stimulation. Unstimulated cells adherent to FN or VN had already released small amounts of IL-8, and both VN- and FN-adherent cells produced, almost invariably, a higher level of cytokines than BSA-exposed cells after additional stimulation. These results show that mast cell adhesion to matrix proteins by itself has only selected and minor effects, but additional activation of mast cells by secretory stimuli causes significantly enhanced 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.