Mucin gene expression in OME: cellular localization

Abstract

Mucins are responsible for the high viscosity of middle ear effusions preventing clearance from the middle ear. Nine mucin genes (MUC genes) have been identified. We have shown at least two biochemically distinct mucins are present in OME and ELISA studies showed no reactivity with MUC1 or MUC2, suggesting low levels of MUC5AC and higher levels of MUC5B. Here we have investigated further immuno histochemically to determine the cellular localization of these gene products. Rabbit polyclonal antisera (TEPA2) were raised to highly purified mucin from thick effusions. The monoclonal antibody NCL-HGM-45M1 was used to probe for MUC5AC. Surgical tissue specimens were fixed in 10% formal saline overnight, wax embedded and sectioned (5 μm). Microwave retrieval was followed with primary antibody then by biotinylated secondary antibody followed by AB complexing and haematoxylin counterstaining (see Table 1). There was no staining of non-mucus secreting cells in test or control tissues. The pattern of staining with TEPA2 in salivary glands, trachea, stomach, and ileum matched that previously reported for MUC5B.1 MUC5AC (NCL-HGM-45M1) was not present in middle ear mucosa but was present in goblet cells of nasal turbinates and probably reflects a low expression of MUC5AC as seen from low levels present in the effusion (5–15% by weight of mucin). TEPA2 stained the mucous glands of middle ear mucosa but not the goblet cells. Based on TEPA2 staining MUC5B is therefore a strong candidate for the mucin produced by middle ear mucosal glands, studies continue to confirm this and to determine the gene product of the goblet cells.