Osteoclast-associated receptor (OSCAR) is specifically expressed by preosteoclasts and it signals through the ITAM-harboring adaptor protein Fc receptor gamma (FCRG) (Merck et al. 2004). Collagen types (Col)I, II, and III have been described as OSCAR ligands, and this interaction induce costimulatory signaling in receptor activator for NF-kB-dependent osteoclastogenesis (Barrow et al. 2011, Schultz et al. 2015).
Surfactant protein D (SP-D) is a member of the collagenous lectins (collectins), which provide a first line of humoral innate immune defense to pathogens at mucosal surfaces. SP-D is mainly produced by alveolar type II epithelial cells, but is also produced outside of the lung, in the gastrointestinal and genital mucosae, salivary glands, prostate, kidney, pancreas, skin, and endothelial cells (Madsen et al. 2000). Polymorphisms in the SP-D-encoding gene SFTPD have been associated with chronic obstructive pulmonary disease and ulcerative colitis. OSCAR binds with SP-D and is localized in an intracellular compartment of alveolar macrophages.This interaction may trigger TNF-alpha productiion by inflammatory monocytes (Barrow et al. 2015).