Acute phase response

IL-6 induces the production of C-reactive protein (CRP) and mannose-binding lectin (MBL) in the liver.

CRP and MBL function like early-evolutionary Abs. Both can activate complement and function as opsonins.

CRP pathway
CRP recognizes phosphocholine on bacterial surfaces.

Similar to the classical pathway, including use of C1q.

MBL pathway
MBL recognizes carbohydrates (mannose sugars) on bacterial surfaces.

Requires MASP-1 and MASP2 to activate complement. MASP (MBL-serine protease) functions like C1q - acts like a protease to activate other C' components.

Other proteins
LPS-binding protein (LBP) for recognition of LPS by TLR-4.

Complement components.