Endothelial Cells: Immunological Aspects

Abstract

It is now clear that the vascular endothelium is not merely a passive vessel wall lining but is actually a multifunctional organ involved in maintaining homeostasis. Strategically located at the interface between blood and the extravascular space, the endothelium is a highly specialised cellular system which plays a key role in physiological processes such as blood supply, nutrient delivery, metabolic homeostasis and immune cell trafficking, as well as pathological processes such as inflammation. Endothelial cells represent a highly heterogeneous population of cells with the ability to interact with and modulate the function of immune cells. These cells regulate the traffic and functions of leucocytes by expressing adhesion molecules and cytokines in a regulated way. The ability of endothelial cells (ECs) to recruit Ag‐specific T cells into the inflammatory sites by displaying cognate major histocompatibility complex (MHC)–peptide complexes contributes a new dimension to the central role played by endothelium in the regulation of immune responses.

Key Concepts:

  • Endothelial cells are not just an inert barrier between the blood and parenchyma.

  • The morphology of the endothelial lining differs between vascular beds.

  • The endothelial cell orchestrates cellular processes key to the inflammatory reaction.

  • A regulated use of different adhesion molecules and chemokines guides tissue‐specific leucocyte extravasation.

  • Selectin ligands are carbohydrates with a common structural motif, the tetrasaccharide sialyl‐Lewis X.

  • Especially, microvascular endothelial cells can act as antigen‐presenting cells.

  • Endothelial cells are both targets for and a source of cytokines – soluble polypeptides acting as mediators of communication with leucocytes and other cells.

Keywords: cytokines; endothelial cells; adhesion molecules; inflammation; chemokines

Figure 1.

The multistep process of leucocyte recruitment.

Figure 2.

Cytokine and bacterial product receptors expressed by endothelial cells. ATF2, activating transcription factor 2; CK, chemokine; DARC, Duffy antigen receptor for chemokines; EPO, erythropoietin; Gb3, globotriaosylceramide; GM‐CSF, granulocyte–macrophage colony‐stimulating factor; HMGI, high mobility group I; IFN‐γ, interferon‐γ; IL‐1, interleukin 1; IL‐1Ra, interleukin 1 receptor antagonist; IRF‐1, interferon regulatory factor 1; L, ligand; LPS, lipopolysaccharide; non‐γc, no common γ chain; PD, positive regulatory domain; PG, proteoglycans; R, receptor; VCAM‐1, vascular cellular adhesion molecule 1; VT, verotoxin. Modified from Mantovani et al..

Figure 3.

Functional programmes activated by cytokines in endothelial cells. Chemokines have both positive and negative effects on endothelial cells. Bold and plain type indicate the relative strengths of activation. EPO, erythropoietin; FGF, fibroblast growth factor; G‐CSF, granulocyte colony‐stimulating factor; GM‐CSF, granulocyte–macrophage colony‐stimulating factor; IFN‐γ, interferon‐γ; IL, interleukin; VEGF, vascular endothelium growth factor. Modified from Mantovani et al..

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Sumitran‐Holgersson, Suchitra, and Holgersson, Jan(Jun 2010) Endothelial Cells: Immunological Aspects. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000513.pub2]