Characterization of α5-Integrin-Dependent Mast Cell Adhesion following FcεRI Aggregation

Abstract

<i>Background:</i> Integrin receptors are engaged in the upregulation of mast cell adhesion to extracellular matrix components upon stimulation with cytokines and antigen. Fibronectin receptor containing the α5-integrin subunit is critical for mast cell interaction with the extracellular matrix protein fibronectin (FN). <i>Methods:</i> The murine MCP5/L mast cell line was employed to investigate the process of Fc&#917;RI-mediated mast cell adhesion to FN. RT-PCR and cytofluorimetric analysis were used to assess the expression of α5 integrin in MCP5/L mast cells. Radiolabelled mast cells were sensitized with monoclonal IgE and used in adhesion assays. Anti-α5-integrin antibody (Ab), monovalent hapten and metabolic inhibitors were used to characterize antigen-mediated mast cell adhesion to FN. <i>Results:</i> Addition of antigen to IgE-sensitized cells resulted in transient upregulation of mast cell adhesion to FN with a maximum adhesion following 30 min of incubation. Mast cell adhesion was inhibited with anti-α5-integrin monoclonal antibodies blocking FN receptor or with excess monovalent hapten preventing antigen-mediated IgE cross-linking. The presence of the protein kinase C (PKC) inhibitor staurosporine also inhibited mast cell adhesion in a dose-dependent fashion. The process of Fc&#917;RI-mediated upregulation of mast cell adhesion to FN was not associated with an increase in surface expression of mast cell FN receptors. <i>Conclusion:</i> The major FN receptor on MCP5/L mast cell surface, an integrin containing the α5 subunit mediates a transient change in mast cell adhesiveness following IgE cross-linking. Fc&#917;RI-derived signals engage PKC and upregulate mast cell adhesion in a process which might involve changes in integrin avidity rather than integrin expression.