Immunohistochemical Localization of Fibrinogen C Domain Containing 1 on Epithelial and Mucosal Surfaces in Human Tissues

Fibrinogen C domain containing 1 (FIBCD1) is a transmembrane receptor that binds chitin and other acetylated compounds with high affinity. FIBCD1 has previously been shown to be present in the epithelium of the gastrointestinal tract. In the present study, we performed a detailed analysis of normally structured human tissues for the expression of FIBCD1 by quantitative PCR and immunohistochemistry. We find that FIBCD1 is expressed in epithelial cells derived from all three germ layers. Endodermal-derived epithelial cells throughout the gastrointestinal tract and the respiratory system showed high expression of FIBCD1 and also mesodermal-derived cells in the genitourinary system and ectodermal-derived epidermis and sebaceous glands cells expressed FIBCD1. In some columnar epithelial cells, for example, in the salivary gland and gall bladder, the FIBCD1 expression was clearly polarized with strong apical reaction, while other columnar cells, for example, in small and large intestine and in bronchi, the staining was equally strong apically and basolaterally. In keratinocytes in skin, tongue, and oral cavity, the FIBCD1 staining was granular. This expression pattern together with the known binding properties supports that FIBCD1 plays a role in innate immunity in the skin and at mucosal surfaces.

Induction of innate immunity by Aspergillus fumigatus cell wall polysaccharides is enhanced by the composite presentation of chitin and beta-glucan

Chitin and β-glucan are conserved throughout evolution in the fungal cell wall and are the most common polysaccharides in fungal species. Together, these two polysaccharides form a structural scaffold that is essential for the survival of the fungus. In the present study, we demonstrated that Aspergillus fumigatus alkali-insoluble cell wall fragments (AIF), composed of chitin linked covalently to β-glucan, induced enhanced immune responses when compared with individual cell wall polysaccharides. Intranasal administration of AIF induced eosinophil and neutrophil recruitment, chitinase activity, TNF-α and TSLP production in mice lungs. Selective destruction of chitin or β-glucan from AIF significantly reduced eosinophil and neutrophil recruitment as well as chitinase activity and cytokine expression by macrophages, indicating the synergistic effect of the cell wall polysaccharides when presented together as a composite PAMP. We also showed that these cell wall polysaccharides induced chitin-specific IgM in mouse serum. Our in vivo and in vitro data indicate that chitin and β-glucan play important roles in activating innate immunity when presented as composite cell wall PAMPs.