Endothelial cell phenotypes in the rheumatoid synovium: activated, angiogenic, apoptotic and leaky

A novel mechanism of neutrophil recruitment in a coculture model of the rheumatoid synovium

OBJECTIVE

Rheumatoid arthritis (RA) is classically thought of as a Th1, T lymphocyte-driven disease of the adaptive immune system. However, cells of the innate immune system, including neutrophils, are prevalent within the diseased joint, and accumulate in large numbers. This study was undertaken to determine whether cells of the rheumatoid stromal microenvironment could establish an inflammatory environment in which endothelial cells are conditioned in a disease-specific manner to support neutrophil recruitment.

METHODS

Human umbilical vein endothelial cells (ECs) and fibroblasts isolated from the synovium or skin of RA patients were established in coculture on opposite sides of porous transwell filters. After 24 hours of EC conditioning, the membranes were incorporated into a parallel-plate, flow-based adhesion assay and levels of neutrophil adhesion to ECs were measured.

RESULTS

ECs cocultured with synovial, but not skin, fibroblasts could recruit neutrophils in a manner that was dependent on the number of fibroblasts. Antibody blockade of P-selectin or E-selectin reduced neutrophil adhesion, and an antibody against CD18 (the beta2 integrin) abolished adhesion. Blockade of CXCR2, but not CXCR1, also greatly inhibited neutrophil recruitment. Interleukin-6 (IL-6) was detectable in coculture supernatants, and both IL-6 and neutrophil adhesion were reduced in a dose-dependent manner by hydrocortisone added to cocultures. Antibody blockade of IL-6 also effectively abolished neutrophil adhesion.

CONCLUSION

Synovial fibroblasts from the rheumatoid joint play an important role in regulating the recruitment of inflammatory leukocytes during active disease. This process may depend on a previously unsuspected route of IL-6-mediated crosstalk between fibroblasts and endothelial cells.

A comparative study of endothelial cell markers expressed in chronically inflamed human tissues: MECA-79, Duffy antigen receptor for chemokines, von Willebrand factor, CD31, CD34, CD105 and CD146

Endothelial cells play a central role in chronic inflammation: for example, they express adhesion molecules and present chemokines leading to enhanced leukocyte recruitment into tissues. Numerous markers of endothelial cells have been reported but there has been a lack of comparative data on their specificity. The present study compared the specificity of seven endothelial cell markers in the rheumatoid synovium and the colon of patients with Crohn's disease. These markers were: the sulphated epitope MECA-79, the Duffy antigen receptor for chemokines (DARC), von Willebrand factor, CD31 (PECAM-1), CD34, CD105 (endoglin) and CD146. MECA-79, DARC and von Willebrand factor showed a specific endothelial cell distribution. MECA-79, which recognizes sulphated ligands for leukocyte adhesion receptor L-selectin (CD62L), was selective for a subset of venules in highly inflamed tissue and was present in rheumatoid but not control osteoarthritic synovia. DARC was also specific for venules but had a more widespread distribution than MECA-79, and was present in rheumatoid and control synovia. The other markers all labelled endothelial cells in venules, arterioles and capillaries. However, they also localized to other cell types. For example, CD34 stained fibroblasts, CD146 was expressed by the pericytes and smooth muscle cells of vessel walls and CD31 and CD105 labelled a broad range of cell types.

Adenosine receptors and the control of endothelial cell function in inflammatory disease

The nucleoside adenosine accumulates in many tissues following the onset of ischaemia and inflammation. This initiates a series of protective mechanisms in target cells upon binding and activation of a family of four G-protein-coupled cell surface adenosine receptor (AR) proteins. The magnitude and duration of adenosine's effects are dictated by the identity and expression levels of each receptor subtype on individual cell types within the hypoxic microenvironment. Given the key role of endothelial cells (ECs) in the development of inflammatory diseases, such as sepsis, rheumatoid arthritis (RA) and atherosclerosis, ARs represent attractive targets for therapeutic intervention in these conditions. In this review, we examine several critical aspects of endothelial function in vivo, assess the role of individual AR subtypes in these events and, where known, discuss the molecular mechanisms by which specific ARs exert their effects.