Identification and characterization of cytokines and adhesion molecules expressed by mucosal mast cells.

The adhesion molecules and cytokines expressed by mucosal mast cells (MMC) were assessed. A gene sequence encoding a beta integrin chain was identified via a cDNA clone derived from a mast cell-specific subtraction library. Sequence analysis of the full-length clone identified it as murine beta7 which shared 85% homology to human beta7. Transcripts were identified in thymus, spleen, and lung. Bone marrow derived mast cells (BMMC) expressed both transcripts and protein encoding beta7,/ /beta1, and alpha4 integrin chains. BMMC expressed another beta7 integrin partner, alphaE, after treatment with transforming growth factor-beta (TGF-beta). MMC directly isolated from the small intestine and lung comprised the majority of alphaE-expressing cells in these organs. Sequences derived from the human alphaE chain were used to obtain the murine alphaE gene. Murine alphaE was 68% homologous to the human gene. The gene product of murine alphaE was immunoprecipitated with antisera to human alphaE and recognized by monoclonal antibodies against murine alphaE. Transcripts encoding alphaE were found in the lung, small intestine, and thymus. Transcription of alphaE is induced in BMMC by treatment with TGF-beta or by degranulation. TGF-beta released by BMMC after degranulation-induced expression of alphaE on responsive T cells at a ratio of one degranulated mast cell to one thousand T cells. Degranulation also modulated the adhesive capability of BMMC via alphaEbeta7 integrin. The alphaEbeta7 integrin adhered to its ligand, E-cadherin, only after cellular activation via phorbol ester treatment or degranulation. A beta1 integrin also mediated this adhesion. Degranulation only initiated adherence of BMMC which already expressed the alphaEbeta7 integrin. Cytokine analysis of BMMC was performed. BMMC cultured in the presence of interleukin (IL)-3 represent a MMC-like phenotype. In contrast, culture in c-kit ligand produces a population of connective tissue mast cell (CTMC)-like cells. Flow cytometric and transcript analysis confirmed that they were mast cells by expression of molecules specific to this cell type. CTMC-like cells transcribed the inflammatory cytokine IL-12 and not the anti-inflammatory cytokine, IL-4, whereas MMC-like cells transcribed IL-4 but not IL-12.