EPITHELIAL CELL-CONDITIONED MEDIA INHIBITS DEGRANULATION OF THE RBL-2H3 RAT MAST-CELL LINE

The effect of epithelial cells on mast cell responses was investigated by examination of degranulation of the rat mast cell line RBL-2H3 aft er overnight culture in media conditioned by the BEAS-2B human bronchi al epithelial cell line [epithelial cell-conditioned media (ECM)]. The se studies indicate that BEAS-2B cells secrete an inhibitor(s) of immu noglobulin E and A-23187-mediated degranulation of the RBL-2H3 cell Li ne. The inhibitory activities of ECM are recovered after filtration th rough a 3-kDa cutoff filter. Pharmacological inhibition of cyclooxygen ase in the BEAS-2B cells before preparation of ECM has no effect on su bsequent inhibition of mast cell degranulation by ECM. However, cycloh eximide treatment of the BEAS-BB cells before the conditioning process does preclude development of mast cell inhibitor activity in ECM, sug gesting that this activity depends on protein synthesis. The effects o f ECM on mast cell function are reversible, demonstrating that these e ffects do not result from overt cytotoxicity. Finally, media condition ed by primary cultures of human respiratory epithelial cells, but not fibroblasts, influence RBL-2H3 degranulation in a manner similar to EC M, suggesting that secretion of mast cell inhibitors may be somewhat u nique to epithelial cells.