Re-establishment of homeostasis and the acute-phase proteins

The stimulation of transcription of acute-phase protein (APP) genes in the liver is incorporated in the complex interchange of cytokines, growth factors and glucocorticoid hormones that are released during the systemic defence reaction in response to trauma. Through the broad spectrum of their activities, this heterogeneous group of circulating proteins assists the injured organism in restoring homeostasis by assuming a protective role. APPs accomplish this by inactivating vasoactive, proteolytic and cytotoxic molecules liberated from damaged tissues and accumulating phagocytic cells, and by participating in a feedback control mechanism that prevents an overload by the organisms' immune response. APP synthesis represents a non-specific response of the liver, in so much as different types of trauma elicit the production of the same proteins. However, data obtained from different laboratory models and clinical observations revealed a certain relationship between the severity and type of trauma and the magnitude of activation of APP gene expression. The observed variations of the overall pattern of APP synthesis point to the existence of different interplays between humoral and cellular mediators capable of adjusting the production of individual proteins to suit different traumas. Hence, changes in the serum concentrations of some APPs have been shown to be useful in monitoring complications such as infection or sepsis after surgery or trauma, and predicting the clinical course of malignant and other diseases. Of the APPs studied in humans, information obtained on CRP and SAA has in particular proved to be a useful indicator of the progression of different pathological states.