What is Mannan-Binding Lectin pathway?
The mannan-binding lectin pathway works in a very similar way to the classical pathway – indeed, most of its steps work the same, and the ultimate intention is production of the membrane attack complex. However, rather than beginning with an antibody-dependent production of the C1 enzyme, this pathway starts with production of a slightly different enzyme. First of all, the mannan-binding protein or MBP binds to mannose groups on the surface of the invador. Many bacteria, for example, are covered with carbohydrates including this mannose group. This in turn allows two further proteins – MASP1 and MASP2 – to bind, producing the first enzyme. This then works in the same way that C1 did, in causing conversion of C4 and C2, allowing their active forms to produce the complex C3 convertase, which is again used to convert C3, and so and and so on (as in the classical pathway) until the MAC is produced. Importantly this provides an innate mechanism which has no involvement of acquired immunity.
