Innate immune defense in the inner ear - mucines are expressed by the human endolymphatic sac

Abstract

The human endolymphatic sac has been shown recently to have immunological capacities and has thus been proposed as the main entity protecting the inner ear from pathogen invasion, equivalent to mucosa-associated lymphoid tissue (MALT). Although the sac expresses molecules of the innate immune system, the potential expression of members of the important mucin family has not been detailed. Thus, this paper explores endolymphatic sac expression of a number of mucins and mucin precursors. Twelve fresh tissue samples from the human endolymphatic sac were obtained during translabyrinthine surgery. The expression of Mucin 1, 2, 5B/AC and 16, as well as the core structure elements (mucin precursors) T-antigen, Tn-antigen and Sialyl-Tn-antigen was investigated by immunohistochemistry. The endolymphatic sac epithelium expressed MUC1 (both apically towards the endolymphatic sac (ES) lumen and basally towards the capillary network), MUC 16 and Tn-antigen. There was no labeling after incubation with antibodies against T-antigen, sialyl-Tn-antigen, MUC2 and MUC5B/AC. We conclude that the human endolymphatic sac epithelium expresses a number of mucin molecules, which supports the hypothesis of the sac as the primary immunological tissue structure of the inner ear, equivalent to MALT in other organs. The mucins may also play a role in the formation and continuous homeostasis of the inner ear fluids, as well as the pathogenesis of Meniere's disease.

Keywords: endolymphatic sac; immunohistochemistry; mucins.

Figure 1

(A) Schematic view of the components of the inner ear.

Figure 2

(A) Survey illustration of a human endolymphatic sac. The section is stained by hematoxylin and eosin. The epithelial lining consists of cuboidal or squamous cells. A loose, vascular connective tissue surrounds the wall of the sac. A large amount of debris is present in the sac cavity. (B) Larger magnification phase contrast illustration of a hematoxylin and eosin stained section. The large cellular projections that protrude into the lumen of the sac are indicated by an arrowhead. The lumen contains mononuclear cells.

Figure 3

Immunohistochemical demonstration of MUC1 in the human endolymphatic sac. The green fluorescence marks the detection of the mucin. The blue fluorescence is caused by 4,6‐diamino‐2‐phenylindole‐2HCl stain in the nuclei. (A) There is an intense labeling of the polyclonal MUC1 antibody in the apical part of most of the epithelial cells in the sac. (B) The staining obtained with the monoclonal anti‐MUC1 antibody 5E5 is present as membrane structures in both the apical and basal parts of epithelial cells. Insert shows stained membrane structures surrounding a nucleus (N). Scale bar: 20 μm.

Figure 4

Immunohistochemical demonstration of the Tn‐antigen and MUC16 in the human endolymphatic sac. The green fluorescence marks the detection of the mucin. The blue fluorescence is caused by 4,6‐diamino‐2‐phenylindole‐2HCl stain in the nuclei. (A) There is a scattered reaction with anti‐Tn in a few saccular epithelial cells. Scale bar: 20 μm. (B) An intense labeling of the MUC16 antibody is present mostly at the basal part of the epithelial cells. Scale bar: 20 μm.