The impact of FCN2 polymorphisms and haplotypes on the ficolin-2 serum levels

Ficolin-2 (L-ficolin), derived from the FCN2 gene, is an innate immunity pattern recognition molecule found in human serum in which inter-individual variation in serum appears to be under genetic control. To validate and extend this finding, we developed a sandwich ELISA for detection of human Ficolin-2 in serum samples and identified FCN2 genotypes with a Taq Man-based minor groove binder assay and by sequencing. Serum samples were applied to gel-permeation chromatography and fractions were analysed by an ELISA, SDS-PAGE and subsequently Western blotting. In 214 Danish blood donors, the median Ficolin-2 serum concentration was determined to 5.4 mu g/ml (range: 1.0-12.2 mu g/ml). An ELISA, SDS-PAGE and Western blot analysis of gel-permeation chromatography fractions showed that Ficolin-2 comprises a mixture of covalently and non-covalently linked Ficolin-2 oligomers independent of the individual genotypes. The variation in serum concentration was associated with three polymorphisms in the promoter and one polymorphism in the structural part of the FCN2 gene. Further analysis indicated that two particular alleles on the same haplotype determined a low Ficolin-2 concentration. Our results show that inter-individual variation of Ficolin-2 concentration is associated with polymorphisms in the promoter and the structural part of the FCN2 gene.