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

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.

