Localization and distribution of fibrinogen C domain containing 1 (FIBCD1) in human tissues

Introduction: We have previously identified and characterized fibrinogen C domain-containing 1 (FIBCD1) as a homotetrameric type II transmembrane protein. FIBCD1 is a member of the fibrinogen- related protein (FReP) family, and is thought to play a crucial role in the innate immune system (Schlosser et al, 2009; Thomsen et al, 2011).
FIBCD1 functions as an endocytic receptor, binding chitin and other acetylated compounds with high affinity. We hypothesize that FIBCD1 serves as a pattern recognition molecule for acetylated compounds, found in various pathogens such as helminths and fungi. We have previously shown that FIBCD1 is present at mucosal surfaces in the lung and large intestine.
Aim: The present study investigates the distribution and localization of FIBCD1 in various healthy human tissues.
Results: We used a monoclonal antibody directed towards the FIBCD1 ectodomain in an immunohistochemistry-based analysis and demonstrate that FIBCD1 protein is highly expressed at the apical surfaces of the epithelium throughout the gastrointestinal tract, in the uterus, testis, bladder, gallbladder and the salivary glands. To a lesser extent, FIBCD1 is expressed in the pancreas, the spleen and the tonsils.
Moreover, using quantitative real-time PCR we demonstrate that FIBCD1 mRNA is highly expressed in the gastrointestinal tract, the lung, the adrenal gland and the testis, which is in coherence with our immunohistochemical findings.
Conclusion: FIBCD1 is present at the apical epithelial surfaces of various mucosal tissues. This strengthens our hypothesis that FIBCD1 is a novel player involved in the innate immune responses of the mucosa.