LYMPHOTACTIN GENE-EXPRESSION IN MAST-CELLS FOLLOWING FC-EPSILON RECEPTOR-I AGGREGATION - MODULATION BY TGF-BETA, IL-4, DEXAMETHASONE, AND CYCLOSPORINE-A

Recruitment of lymphocytes is a prominent feature of allergic inflamma tion. However, the mechanisms by which lymphocytes are attracted to su ch sites are not understood. Recently, cDNAs encoding a lymphocyte-spe cific chemokine, lymphotactin (Ltn), were isolated from mouse pro-T ce ll and human CD8(+) T cell libraries, leading us to hypothesize that m ast cells might also produce Ltn. Using the reverse transcriptase-PCR and Northern blot analysis, we found that the Ltn gene is inducible in C1.MC/C57.1 and murine bone marrow-cultured mast cells (BMCMC) by Fc epsilon RI aggregation. Activation of a human mast cell (HMC-1) or bas ophil cell line (KU812) similarly led to transcription of Ltn. Fc epsi lon RI aggregation-dependent Ltn mRNA expression was detected by 1 to 2 h, maximal at 6 h, independent of de novo protein synthesis, and was inhibited by cyclosporin A and dexamethasone. Compared with macrophag e inflammatory protein alpha (MIP-1 alpha), Fc epsilon RI-dependent Lt n and MIP-1 alpha mRNA levels were up-regulated by IL-4, but not IFN-g amma, although higher levels of IL-4 (100 and 1000 U/ml) inhibited Ltn expression only; and TCF-beta preferentially enhanced Fc epsilon RI-d ependent Ltn mRNA levels, suggesting that Ltn and MIP-1 alpha have sha red and unique regulatory mechanisms. A rabbit polyclonal Ab against a synthetic peptide was developed for use in immunoblot analysis and de tected a 15-kDa Ltn protein within mast cell pellets and in the supern atants of mast cells following Fc epsilon RI aggregation. Ltn is thus expressed in mast cells and may contribute to the recruitment of lymph ocytes to areas of allergic inflammation.