Disease Areas \ Inflammation \ Read More \ About Inflammation \ The acute phase reaction
The acute phase proteins
Authors: Anne Husebekk, MD, Ph.D., Department of Immunology and Transfusion Medicine, University Hospital of Tromsų, Norway
and
Lars-Olof Hansson, MD, Ph.D., Department of Medical Sciences, University Hospital, Uppsala, Sweden
(Ref. 4)
Induction of the acute phase reaction means changes in the synthesis of many proteins which can be measured in plasma. Regulation of protein synthesis takes place at the level of both transcription (DNA, RNA) and translation to protein. The cells have intricate systems for up- and down-regulation of protein synthesis, initiated by a complex system of signals induced in the acute phase reaction. Most of the proteins with increased serum concentrations have functions which are easily related to limiting the negative effects of the acute phase stimulus or to the repair of inflammatory induced damage. Examples are enzyme inhibitors limiting the negative effect of enzymes released from neutrophils, scavengers of free oxygen radicals, increase in some transport proteins and increased synthesis and activity of the cascade proteins such as coagulation and complement factors (Table III). The synthesis may be upregulated even if plasma levels are normal, due to increased consumption of acute phase proteins.
Two of the proteins which have the most pronounced increase, namely serum amyloid A protein (SAA) and C-reactive protein (CRP) have less defined functions, although understanding about the function of CRP has increased over the last years. The changes in three important proteins and the erythrocyte sedimentation rate (ESR) are shown in Fig. 3.
Table III Some of the more well-known acute phase proteins, their functions and changes in plasma level during the acute phase reaction.
Function
Acute phase protein
Increase up to
Protease inhibitors
Alpha 1-antitrypsin Alpha 1-antichymotrypsin
4 fold 6 fold
Coagulation proteins
fibrinogen prothrombin factor VIII plasminogen
8 fold
Complement factors
C1s C2b C3, C4, C5 C9 C5b
2 fold
Transport proteins
haptoglobin haemopexin ferritin
8 fold 2 fold 4fold
Scavenger proteins
ceruloplasmin
4 fold
Miscellaneous
"a1-acid glycoprotein (orosomucoid) serum amyloid A protein C-reactive protein
