Acute-phase Protein - Positive

Positive

Positive acute-phase proteins serve different physiological functions for the immune system. Some act to destroy or inhibit growth of microbes, e.g., C-reactive protein, mannose-binding protein, complement factors, ferritin, ceruloplasmin, Serum amyloid A and haptoglobin. Others give negative feedback on the inflammatory response, e.g. serpins. Alpha 2-macroglobulin and coagulation factors affect coagulation, mainly stimulating it. This pro-coagulant effect may limit infection by trapping pathogens in local blood clots. Also, some products of the coagulation system can contribute to the innate immune system by their ability to increase vascular permeability and act as chemotactic agents for phagocytic cells.

"Positive" acute-phase proteins:
Protein Immune system function
C-reactive protein Opsonin on microbes
Serum amyloid P component Opsonin
Serum amyloid A
  • Recruitment of immune cells to inflammatory sites
  • Induction of enzymes that degrade extracellular matrix
Complement factors Opsonization, lysis and clumping of target cells. Chemotaxis
Mannan-binding lectin Mannan-binding lectin pathway of complement activation
Fibrinogen, prothrombin, factor VIII,
von Willebrand factor		 Coagulation factors, trapping invading microbes in blood clots.
Some cause chemotaxis
Plasminogen Degradation of blood clots
Alpha 2-macroglobulin
  • Inhibitor of coagulation by inhibiting thrombin.
  • Inhibitor of fibrinolysis by inhibiting plasmin
Ferritin Binding iron, inhibiting microbe iron uptake
Hepcidin Stimulates the internalization of ferroportin, preventing release of iron bound by ferritin within intestinal enterocytes and macrophages
Ceruloplasmin Oxidizes iron, facilitating for ferritin, inhibiting microbe iron uptake
Haptoglobin Binds hemoglobin, inhibiting microbe iron uptake
Orosomucoid
(Alpha-1-acid glycoprotein, AGP)		 Steroid carrier
Alpha 1-antitrypsin Serpin, downregulates inflammation
Alpha 1-antichymotrypsin Serpin, downregulates inflammation

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