Acute inflammation involves two major physiological responses that alter the temperature set point in the hypothalamus (the 'febrile response') and plasma protein metabolism in the liver. During non-inflammatory conditions, the liver produces steady state concentrations of range of plasma proteins. The plasma concentration of acute phase proteins changes in response to inflammation. Most acute phase proteins increase in concentration by a factor of several fold. However, the levels of major acute phase proteins can change in excess of a thousand fold higher than normal values. Acute phase protein concentrations can decrease (i.e. Serum Albumin, Transferrin, RBP4) as well as increase (i.e. C-Reactive Protein, alpha-2-Macroglobulin, Serum Amyloid) following exposure to inflammatory conditions.
C-Reactive Protein (CRP) is possibly the most studied acute phase protein. Plasma concentrations of CRP increase dramatically following inflammation. Importantly, the increase in CRP levels reflects the intensity of inflammation. Up to a thousand fold increase in CRP can be detected following infection, trauma, surgery, and burns, while more moderate increases are associated with exercise and stress.