The biological role of IL-1, IL-6 and CRP and their application in the diagnosis of the inflammatory process

Abstract

Activation of inflammation is a type of innate, non-specific defence of the body against harmful factors of external or internal origin. During this process, various types of cytokines are released, including interleukin-1 (IL-1) and interleukin-6 (IL-6), responsible for the intensification of inflammatory reactions and the activation of hepatic acute phase proteins synthesis. IL-1 exists in two isoforms (IL-1α and IL-1β), showing similar, pro-inflammatory biological properties, but differing in origin, place of release and method of activation. The use of IL-1 in the diagnosis of the inflammatory process is limited, mainly due to the short half-life of this cytokine. IL-6 has a pleiotropic nature of action by using different types of receptors signaling. IL-6 is responsible for activating the synthesis of a wide range of acute phase proteins, also is involved in hematopoiesis and the immune response. IL-6 is a good biomarker of the early phase of inflammation because it has a longer half-life than other cytokines, and its concentration in the blood may increase several thousand times during the first hours after the initiation of inflammation. Due to its high sensitivity in detecting inflammation, C-reactive protein is the most commonly determined highly positive acute phase protein. During the inflammatory process, the pentameric CRP isoform (pCRP) dissociates into monomeric CRP (mCRP), which changes the anti-inflammatory properties of CRP into highly pro-inflammatory. The currently used laboratory tests detect only the pCRP isoform, because it is well soluble in blood and accumulates in it when conversion to mCRP is no longer effective.