Osteopontin is increased in cystic fibrosis and can skew the functional balance between ELR-positive and ELR-negative CXC-chemokines

BackgroundThe glycoprotein osteopontin plays important roles in several states of disease associated with inflammation, for example by recruiting neutrophils but its expression and possible roles in cystic fibrosis (CF) have not been investigated.MethodsImmunohistochemistry and ELISA were used to detect osteopontin in clinical samples. In addition, osteopontin-binding and functional interference with antibacterial (ELR-negative) and neutrophil-recruiting (ELR-positive) CXC-chemokines were investigated using in vitro assays.ResultsIncreased osteopontin-expression was found in the airways of CF patients compared with controls. Interestingly, osteopontin bound to ELR-negative CXC-chemokines, reducing their antibacterial and receptor-activating properties while no binding or interference with the function of ELR-positive chemokines was found.ConclusionsHigh expression of osteopontin is likely part of the dysregulated inflammation seen in CF, impairing the activities of ELR-negative chemokines that both serve as innate antibiotics and recruit NK and cytotoxic T cells, instead promoting an excessive influx of neutrophils, and may thus contribute to disease progress.