Detection and characterization of OX40 ligand expression in human airway smooth muscle cells: A possible role in asthma?

Background: The airway smooth muscle (ASM) cell, originally thought of as a passive structural cell, is now well recognized as an active participant in the pathologic events that occur during persistent asthma. Cell-surface molecules play an important role in the development of an immune response. A number of cell-surface molecules are expressed on ASM cells, and these might contribute to the inflammatory reaction. Objective: The purpose of this study was to determine whether OX40 ligand (OX40L), a molecule known to be involved in T-cell activation, was present on the ASM cell surface. Methods: We used real-time RT-PCR to detect mRNA expression and flow cytometry, ELISA, and immunoprecipitation to detect the presence of cell-surface protein on ASM cells isolated from asthmatic and nonasthmatic individuals. ELISAs and Western blotting were used to determine the functional outcomes of engagement of OX40L. Results: OX40L was present on both asthmatic and nonasthmatic ASM cells. Engagement of OX40L with recombinant OX40:Fc resulted in a significantly greater increase in release of IL-6 from ASM cells of asthmatic patients than from ASM cells of nonasthmatic patients (P < .01). Ligation of OX40L resulted in a rapid translocation of protein kinase C beta(2) to the cell membrane. Conclusion: Because the receptor for OX40L, OX40, is expressed on CD4(+) T cells within 48 hours of stimulation through the T-cell receptor, elucidation of the cross-talk between OX40 and OX40L could be very important in understanding the interaction of cells present in the inflamed airways of an asthmatic patient.