MIF and CD74 - suitability as clinical biomarkers.

Macrophage migration inhibitory factor (MIF) is a pleiotropic immunoregulatory cytokine whose effects on arresting 'random' immune cell movement was already recognized decades ago. MIF is quasi-constitutively expressed by a variety of different cells and tissues, including immune cells such as T-cells and monocytes/macrophages, but also nonimmune cells like certain endocrine cells and cells lining interior body cavities or contacting the exterior environment, such as endothelial cells (ECs), or epithelial cells in kidney, gut and skin. Contrary to its historic name, MIF has a direct chemokine-like function and promotes 'directed' cell migration (i.e. chemotaxis) and plays a prominent role in inflammatory and atherogenic leukocyte recruitment. At the molecular level, these activities are based on a non-cognate interaction between MIF and the CXC chemokine receptors CXCR2 and CXCR4. Importantly, MIF also interacts with surface CD74, a type II transmembrane protein, inducing its phosphorylation and the recruitment of CD44, leading ultimately to ERK1/2 phosphorylation. Multiple studies have pointed to the utility of MIF as a biomarker for different diseases that have an inflammatory component; these include systemic infections and sepsis, cancer, autoimmune diseases as well as different metabolic disorders. In this Review, we highlight the suitability of MIF and CD74 as biomarkers for different disease applications.