Description
Ficolins are a group of proteins containing both a collagen-like domain and a fibrinogen-like domain. Three forms of ficolins have been identified in humans: Ficolin-1 (M-ficolin), Ficolin-2 (L-ficolin),and Ficolin-3 (H-ficolin). Ficolin-2 is produced primarily by the liver. Whereas Ficolin-3 is produced by the liver and the lung and Ficolin-1 by monocytes, leukocytes and lung cells. Ficolin-2 recognizes distinct danger-associated molecular patterns (DAMPs) like GlcNAc-structures in Lipoteichoic Acid (LTA) and fungal 1,3-β-D-glucan. Ficolin-2 also recognizes N-acetylated compounds such as acetylcholine. Furthermore, Ficolin-2 recognizes apoptotic cells and participates in the removal of host cells. Ficolin-2 circulates in complex with MASP-2 and can activate the lectin complement pathway. Ficolin-2 serum levels are reported with varying concentrations. Polymorphisms in the promoter of the FCN2 gene from which Ficolin-2 is derived are associated with variation in Ficolin-2 serum levels. These polymorphisms may influence the affinity of Ficolin-2 to GlcNAc-structures. Ficolin-2 deficiencies have not been reported, but low Ficolin-2 serum levels have been associated with recurrent respiratory infections in children. Interestingly, Ficolin-2 has been implicated in the unique immune challenge during pregnancy. In maternal plasma of normal pregnancies, a 4- to 5-fold increase in Ficolin-2 was detected compared to healthy non-pregnant persons. However, significantly lower Ficolin-2 maternal plasma concentrations were associated with pre-eclamptic pregnancies. Therefore, assessment of Ficolin-2 is warranted to study its regulatory role in the innate immune system. Normal human plasma contains a Ficolin-2 concentration ranging from 1 to 14 µg/ml