Table 1.

Comparison of MBL and the ficolins emphasising their contribution to respiratory infection defences

Lectin	Tissue expression	Location	Function	Binding to respiratory organisms	Association with RTI
MBL	liver	serum; sites of inflammation including respiratory epithelial surface	lectin pathway activation; mediates opsonophagocytosis; clearance of apoptotic cells	H. influenzae M. pneumoniae influenza virus M. tuberculosis L. pneumophila	invasive pneumococcal disease; community-acquired pneumonia; tuberculosis; Legionnaires' disease; SARS; progression of cystic fibrosis
L-ficolin	liver	serum	lectin pathway activation; mediates opsonophagocytosis; clearance of apoptotic cells	S. pneumoniae serotypes 11A 11D 11F	recurrent RTI in children
M-ficolin	monocytes; lung type II alveolar cells; spleen	PBMC surface; possibly respiratory epithelial surface	mediates opsonophagocytosis	not detected	not studied
H-ficolin	lung type II alveolar cells and bronchial epithelial cells; liver	respiratory epithelial surface; serum	lectin pathway activation; clearance of apoptotic cells	not studied	not studied

RTI = Respiratory tract infection; PBMC = peripheral blood mononuclear cell.