Background: Human lung mast cells (HLMCs) infiltrate the airway epithelium and airway smooth muscle (ASM) in\nasthmatic airways. The mechanism of HLMC adhesion to both cell types is only partly defined, and adhesion is not\ninhibited by function-blocking anti-Kit and anti-stem cell factor (SCF) antibodies. Our aim was to identify adhesion molecules\nexpressed by human mast cells that mediate adhesion to human ASM cells (HASMCs) and human airway epithelial cells.\nMethods: We used phage-display to isolate single chain Fv (scFv) antibodies with adhesion-blocking properties from rabbits\nimmunised with HLMC and HMC-1 membrane proteins.\nResults: Post-immune rabbit serum labelled HLMCs in flow cytometry and inhibited their adhesion to human BEAS-2B\nepithelial cells. Mast cell-specific scFvs were identified which labelled mast cells but not Jurkat cells by flow cytometry.\nOf these, one scFv (A1) consistently inhibited mast cell adhesion to HASMCs and BEAS-2B epithelial cells by about\n30 %. A1 immunoprecipitated Kit (CD117) from HMC-1 lysates and bound to a human Kit-expressing mouse mast cell\nline, but did not interfere with SCF-dependent Kit signalling.\nConclusion: Kit contributes to human mast cell adhesion to human airway epithelial cells and HASMCs, but may utilise\na previously unidentified adhesion domain that lies outside the SCF binding site. Targeting this adhesion pathway\nmight offer a novel approach for the inhibition of mast cell interactions with structural airway cells, without detrimental\neffects on Kit signalling in other tissues.
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