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.
| Protein | Immune system function |
|---|---|
| C-reactive protein | Opsonin on microbes |
| Serum amyloid P component | Opsonin |
| Serum amyloid A |
|
| 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 |
|
| 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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