Collectins: collagenous C-type lectins of the innate immune defense system.

Collectins are humoral lectins found in mammals and birds. They are oligomers whose subunits comprise three polypeptide chains each containing a collagenous section and a C-terminal lectin domain. They are related structurally and functionally to the first component of the classical complement pathway, C1q, and seem to serve important roles in innate immunity through opsonization and complement activation. The lectin domains bind carbohydrates on microorganisms, while the collagenous regions are ligands for the collectin receptor on phagocytes and also mediate C1q-independent activation of the classical complement pathway.