Mannan‐Binding Lectin, L‐Ficolin and H‐Ficolin Selectively Binds to Different Bacteria

Krarup, A.; Sørensen, U.; Matsushita, M.; Jensenius, J. C.; Thiel, S.

Mannan‐binding lectin (MBL), L‐ficolin and H‐ficolin are pattern recognition molecules of the innate immune system. We investigated the ability of these molecules to bind to different serotypes and noncapsulated variants of Streptococcus pneumonia and Staphylococcus aureus. We found that MBL binds to noncapsulated S. aureus strain (Wood) but not any of the examined S. pneumoniae serotypes. L‐ficolin binds to some capsulated S. pneumoniae serotypes (11A, 11D and 11F) as well as some capsulated S. aureus serotypes (Type‐1, ‐8, ‐9, ‐11 and ‐12). H‐ficolin does not bind to any of the examined S. pneumoniae and S. aureus serotypes included in this study but did bind to a strain of Aerococcus viridans. When bound to bacteria, MBL and H‐ficolin initiated activation of complement factor C4, whereas L‐ficolin did not. During this study, quantitative assays for the three proteins were developed and the concentration in 97 plasma samples were determined and the median values were estimated at 0.8 μg of MBL/ml, 3.3 μg of L‐ficolin/ml and 18.4 μg of H‐ficolin/ml, respectively.