CRP is an acute-phase inflammatory protein present in the plasma. In the presence of calcium, CRP binds to polysaccharides on microorganisms and triggers the classical complement pathway of innate immunity by activating C1q. CRP is produced by the liver, smooth muscle, macrophages, endothelial cells, lymphocytes, and adipocytes. It is transcribed in hepatocytes in the liver in response to increased levels of inflammatory cytokines such as IL-6 and IL-1. CRP expression can increase by up to 1000-fold during inflammatory conditions such as acute bacterial infections or with severe tissue damage. It is used as a clinical marker of inflammation and infection.