An evolving new paradigm: endothelial cells – conditional innate immune cells
1 Centers of Metabolic Disease Research, Cardiovascular Research, Thrombosis Research, Department of Pharmacology, Temple University School of Medicine, Philadelphia, PA 19140, USA
2 Department of Family Medicine, College of Community Health Sciences, University of Alabama, Tuscaloosa, AL 35487, USA
Journal of Hematology & Oncology 2013, 6:61 doi:10.1186/1756-8722-6-61Published: 22 August 2013
Endothelial cells (ECs) are a heterogeneous population that fulfills many physiological processes. ECs also actively participate in both innate and adaptive immune responses. ECs are one of the first cell types to detect foreign pathogens and endogenous metabolite-related danger signals in the bloodstream, in which ECs function as danger signal sensors. Treatment with lipopolysaccharide activates ECs, causing the production of pro-inflammatory cytokines and chemokines, which amplify the immune response by recruiting immune cells. Thus, ECs function as immune/inflammation effectors and immune cell mobilizers. ECs also induce cytokine production by immune cells, in which ECs function as immune regulators either by activating or suppressing immune cell function. In addition, under certain conditions, ECs can serve as antigen presenting cells (antigen presenters) by expressing both MHC I and II molecules and presenting endothelial antigens to T cells. These facts along with the new concept of endothelial plasticity suggest that ECs are dynamic cells that respond to extracellular environmental changes and play a meaningful role in immune system function. Based on these novel EC functions, we propose a new paradigm that ECs are conditional innate immune cells. This paradigm provides a novel insight into the functions of ECs in inflammatory/immune pathologies.