MAST-CELLS INDUCE T-CELL ADHESION TO HUMAN FIBROBLASTS BY REGULATING INTERCELLULAR-ADHESION MOLECULE-1 AND VASCULAR CELL-ADHESION MOLECULE-1 EXPRESSION

The capacity of mast cell products to mediate T-cell adhesion to fibro blasts was explored using heterotypic coculture systems or by exposing fibroblasts to mast-cell-conditioned media (MCCM), prepared by degran ulating mast cells with calcium ionophore, Experimental results indica ted that fibroblasts exposed to MCCM for 24 h bound fivefold more T ce lls than control fibroblasts. Binding was inhibited with intercellular adhesion molecule-1 (ICAM-1) or vascular cell adhesion molecule-1 (VC AM-1) neutralizing antibodies, Enzyme-linked immunosorbent assay and f luorescence-activated cell sorter analysis revealed that fibroblasts e xposed to MCCM markedly increased ICAM-1 and VCAM-1 surface expression by 4 h, with levels maximal at 16 h and returning toward baseline by 48 h. A dose-dependent response of ICAM-1 and VCAM-1 expression was no ted using serial dilutions of MCCM of by altering the ratio of degranu lated mast cells cocultured with fibroblasts. Similar results were obt ained using human fibroblasts derived from the dermis, synovium, and l ung, although lung fibroblasts were generally less responsive, Norther n analysis confirmed that MCCM regulated ICAM-1 and VCAM-1 expression at the mRNA level. In summary, mast cell products stimulated fibroblas t surface expression, steady-state mRNA levels, and functional express ion of ICAM-1 and VCAM-1, Experimental data suggest that mast-cell-der ived tumor necrosis factor-alpha map be in large part responsible for these observations, although further studies using human mast cells wi ll be required, Using a skin-equivalent organotypic coculture model wi th fibroblasts admired with mast cells, we observed increased ICAM-1 e xpression in both keratinocytes and fibroblasts after activation of th e mast cells.