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Acute-phase protein
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<p>Acute-phase proteins (APPs) are a class of <a href="/facts/Protein/Jxmagu3E">proteins</a> whose concentrations in <a href="/facts/Blood_plasma/oHuwwugG">blood plasma</a> either increase (positive acute-phase proteins) or decrease (negative acute-phase proteins) in response to <a href="/facts/Inflammation/Ura86MIy">inflammation</a>. This response is called the <i>acute-phase reaction</i> (also called <i>acute-phase response</i>). The acute-phase reaction characteristically involves <a href="/facts/Fever/waVxR2Ac">fever</a>, acceleration of peripheral <a href="/facts/Leukocytes/vsDunUK0">leukocytes</a>, circulating <a href="/facts/Neutrophil/KL6oTt8b">neutrophils</a> and their precursors. The terms <i>acute-phase protein</i> and <i>acute-phase reactant</i> (APR) are often used synonymously, although some APRs are (strictly speaking) <a href="/facts/Polypeptide/C4ltc7UG">polypeptides</a> rather than proteins. </p><p>In response to <a href="/facts/Injury/PJ7CbnMQ">injury</a>, local <a href="/facts/Inflammation/Ura86MIy">inflammatory</a> <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a> (<a href="/facts/Neutrophil_granulocyte/KL6oTt8b">neutrophil granulocytes</a> and <a href="/facts/Macrophage/z7hkQu3o">macrophages</a>) secrete a number of <a href="/facts/Cytokine/SdWpWABH">cytokines</a> into the bloodstream, most notable of which are the <a href="/facts/Interleukin/a8qBzb0E">interleukins</a> <a href="/facts/Interleukin_1/dSToCWMd">IL1</a>, and <a href="/facts/Interleukin_6/FVQeAWkt">IL6</a>, and <a href="/facts/Tumor_necrosis_factor-alpha/7NWNIaCb">TNF-α</a>. The <a href="/facts/Liver/Rtp4Fk2b">liver</a> responds by producing many acute-phase reactants. At the same time, the production of a number of other <a href="/facts/Protein/Jxmagu3E">proteins</a> is reduced; these <a href="/facts/Protein/Jxmagu3E">proteins</a> are, therefore, referred to as "negative" acute-phase reactants. Increased acute-phase proteins from the <a href="/facts/Liver/Rtp4Fk2b">liver</a> may also contribute to the promotion of <a href="/facts/Sepsis/n52bkffJ">sepsis</a>. </p>