Characteristics and Biological Variations of M-Ficolin, a Pattern Recognition Molecule, in Plasma

Abstract

The three human ficolins, H-ficolin, L-ficolin and M-ficolin, are pattern recognition molecules of the innate immune system. All three ficolins can activate the lectin pathway of the complement system after binding to pathogens. H- and L-ficolin are serum proteins with an average concentration of 18 and 3 µg/ml, respectively. M-ficolin has been described as a membrane-associated pattern recognition receptor of monocytes, being also present in granulocytes; recently, minuscule amounts of M-ficolin have been found in serum, too. No assay specific for M-ficolin has yet been described and biological variations are unknown. We have raised specific monoclonal anti-human M-ficolin antibodies and have developed a quantitative assay for M-ficolin. M-ficolin elutes as a large, 900-kDa protein upon gel permeation chromatography of serum. Analysis of M-ficolin levels in serum samples of 350 blood donors reveals a mean concentration of 1.07 µg/ml, ranging from 0.28 to 4.05 µg/ml. Analyses of consecutive acute phase serum samples from major surgery patients indicated a complex response. Ontogeny was investigated through cord blood samples from healthy full-term babies, which showed adult levels, with sequential samples showing no increase from birth to 1 year of age. We suggest that M-ficolin should also be considered as a humoral pattern recognition molecule.

Studies of the Pattern Recognition Molecule H-ficolin

“…The concentration of H-ficolin was read from a calibration curve constructed using serial dilutions of a local standard serum pool (27). The concentrations of MBL and M-ficolin were quantified in a similar manner using anti-MBL and anti-M-ficolin antibodies, respectively (2,40).…”

“…Recognition in innate immunity relies on the ability of pattern-recognition molecules (PRMs) 2 to bind foreign markers, the so-called pathogen-associated molecular patterns (PAMPs). One group of PRMs is able to initiate activation of the complement system upon binding.…”

“…One group of PRMs is able to initiate activation of the complement system upon binding. The group is composed of mannan-binding lectin (MBL) and the three ficolins (H-, L-, and M-ficolin) (1,2). Both MBL and ficolins recognize specific structures presented in an organized pattern on the surface of pathogens but also structures on apoptotic or necrotic cells.…”

“…: 45-8942-1776; Mobile: 45-2927-0890; E-mail: st@microbiology.au.dk. 2 The abbreviations used are: PRM, pattern recognition molecule; MBL, mannan-binding lectin; MASP, MBL-associated serine protease; AcBSA, acetylated bovine serum albumin; C4, complement factor C4; PAMP, pathogenassociated molecular pattern; BisTris, 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol; IEC, ion exchange chromatography; TRIFMA, time-resolved immunofluorometric assay; tw, Tween 20; HSA, human serum albumin; GPC, gel permeation chromatography.…”

“…H-ficolin is also found in the mucosa of the lung where it originates from bronchial epithelial cells and alveolar type II epithelial cells (25). The mean serum concentration of H-ficolin is 18.4 g/ml, as compared with 3.3 and 1.07 g/ml for L-and M-ficolin, respectively, and H-ficolin is thus the most abundant PRM of the lectin pathway (2,27). H-ficolin has only been characterized in humans, but based on data base sequence alignment, orthologs of the human H-ficolin gene (FCN3, chromosome 1p36.11) are identified in both lower and higher primates as well as in other lower species such as mouse, rat, and cat (28,29).…”