Expression of M-Ficolin in human monocytes and macrophages

M-Ficolin is a member of the ficolin family of proteins, which is expressed by monocytes. We have determined the expression of this gene in various populations of this lineage in man and found lower levels of M-Ficolin mRNA in the more mature CD14(+)CD16(+) monocytes as compared to the classical CD14(++) monocytes. Monocyte-derived macrophages generated by in vitro culture for 5 days strongly reduced M-Ficolin mRNA and protein. Mature tissue macrophages from the lung and from breast milk also showed a very low level of M-Ficolin transcripts. When cells of the monocytic cell line Mono Mac 6 cell were treated with TLR2 and TLR4 ligands for 24 h then there was an average of 6- and 9-fold induction of the M-Ficolin mRNA, respectively. After 72 h induction was in average 30- and 80-fold for TLR2 and TLR4 stimulation, respectively. Treatment of monocyte-derived macrophages for 3 days with TLR4 ligand gave an average 4-fold induction and alveolar macrophages treated with TLR4 ligand showed a 12-fold induction. These data show that M-Ficolin expression is silenced in macrophages but can be re-activated after prolonged activation via TLRs.