Mannose-Binding Lectin

Abstract Mannose-binding lectin (MBL) is an oligomeric, calcium-dependent lectin of the collectin subfamily. It is a pattern-recognition molecule, specific for a broad spectrum of nonself (and altered self) ligands. It acts as an opsonin and activates the lectin pathway of complement (in association with MBL-associated serine proteases). MBL is synthesised in the liver and secreted into the blood stream where its concentration/activity is enormously affected by polymorphisms of the MBL2 gene. The best characterised are located in exon 1 (codons 52 [A/D], 54 [A/B] and 57 [A/C], collectively A/O) and in the promoter (−550 [H/L] and −221 [Y/X]). MBL is thought to be an important component of innate immunity, functioning as an opsonic ante-antibody and also influencing cellular immunity through dendritic cells. MBL deficiency has been described as contributing to a huge variety of clinical disorders. However, MBL overactivity and resulting inflammation may be harmful to the host.