Differential release and deposition of S100A8/A9 proteins in inflamed upper airway tissue

Intracellular Ca2+-binding S100A8/A9 proteins gain novel functions when released during inflammation. The exact outcome of their extracellular function depends on the local tissue environment in which they are released; both anti-inflammatory and pro-inflammatory responses are described, modulating the immune system by binding Toll-like receptor (TLR)-4 or the receptor for advanced glycation end-products (RAGE). However, the contribution of the proteins in the pathophysiology of chronic rhinosinusitis (CRS) remains unclear. Homomeric S100A8 and S100A9, and heteromeric S100A8/A9 proteins were evaluated in CRS with/without nasal polyps (CRSw/sNP) and controls. Functional responses were assessed in polyp tissue stimulated with S100 proteins in the presence of TLR-4 and RAGE blocking antibodies. S100A8, S100A9 and S100A8/A9 protein levels were significantly higher in CRSwNP patients, showing increased deposition on extracellular matrix (ECM) structures of CRSwNP tissue in contrast to CRSsNP and controls. In the presence of Staphylococcus aureus, S100A8/A9 is released from neutrophils and from the ECM. Extracellular S100A8 and S100A9 proteins induced increased levels of diverse inflammatory mediators via TLR-4 engagement. The inflammatory/remodelling characteristics of CRSwNP specifically allow increased retention of S100A8, S100A9 and S100A8/A9 proteins in the ECM of CRSwNP tissue. Upon release, homodimeric proteins act as a local danger signal inducing inflammatory mediators, predominantly via TLR-4 activation.