The 3G5 antigen is expressed in dermal mast cells but not pericytes

Pericytes in the Lung

The lung has numerous roles, including gas exchange, immune surveillance, and barrier function. Being a highly vascularized organ, the lung receives dual blood supply from both the pulmonary and bronchial circulation. Therefore, pericytes likely play a prominent role in lung physiology given their localization in the perivascular niche. New genetic approaches have increased our understanding of the origin and the diverse functions of lung pericytes. Lung pericytes are myofibroblast progenitors, contributing to development of fibrosis in mouse models. Lung pericytes are also capable of responding to danger signals and amplify the inflammatory response through elaboration of cytokines and adhesion molecules. In this chapter, we describe the molecular, anatomical, and phenotypical characterization of lung pericytes. We further highlight their potential roles in the pathogenesis of lung diseases including pulmonary fibrosis, asthma, and pulmonary hypertension. Finally, current gaps in knowledge and areas of ongoing investigation in lung pericyte biology are also discussed.

Cultured Human Adipose Tissue Pericytes and Mesenchymal Stromal Cells Display a Very Similar Gene Expression Profile

Mesenchymal stromal cells (MSCs) are cultured cells that can give rise to mature mesenchymal cells under appropriate conditions and secrete a number of biologically relevant molecules that may play an important role in regenerative medicine. Evidence indicates that pericytes (PCs) correspond to mesenchymal stem cells in vivo and can give rise to MSCs when cultured, but a comparison between the gene expression profiles of cultured PCs (cPCs) and MSCs is lacking. We have devised a novel methodology to isolate PCs from human adipose tissue and compared cPCs to MSCs obtained through traditional methods. Freshly isolated PCs expressed CD34, CD140b, and CD271 on their surface, but not CD146. Both MSCs and cPCs were able to differentiate along mesenchymal pathways in vitro, displayed an essentially identical surface immunophenotype, and exhibited the ability to suppress CD3(+) lymphocyte proliferation in vitro. Microarray expression data of cPCs and MSCs formed a single cluster among other cell types. Further analyses showed that the gene expression profiles of cPCs and MSCs are extremely similar, although MSCs differentially expressed endothelial cell (EC)-specific transcripts. These results confirm, using the power of transcriptomic analysis, that PCs give rise to MSCs and suggest that low levels of ECs may persist in MSC cultures established using traditional protocols.

Spontaneous fibroblast-derived pericyte recruitment in a human tissue-engineered angiogenesis model in vitro

Cooperation between endothelial cells and pericytes is essential to the stabilization and maturation of blood microvessels. We developed a unique in vitro tissue-engineered model to study angiogenesis. The human endothelialized reconstructed connective tissue model promotes the formation of a three-dimensional branching network of capillary-like tubes (CLT) with closed lumens. The purpose of this work was to investigate whether pericytes were spontaneously recruited around CLT in the model. We demonstrated that smooth muscle α-actin (SMA)-positive cells were found closely associated with PECAM-1-positive capillaries in the model. Twelve percent (±2.6) of SMA-positive cells were detected along with 15% (±1.64) von Willebrand factor-positive endothelial cells in the culture system after 31 days of in vitro maturation. Conversely, no SMA-positive cells were detected in reconstructed connective tissues made solely of fibroblasts. Knowing that PDGF is a major factor in the recruitment of pericytes, we showed that blockade of the PDGFB receptor using the inhibitor AG1296 induced an overall 5, 2.6, and 2.4-fold decrease in the SMA-positive cells, von Willebrand factor-positive cells, and number of capillaries, respectively. Using combinations of human GFP-positive fibroblasts and endothelial cells, we demonstrated that pericytes were recruited from the fibroblast population in the model. In conclusion, our tissue-engineered culture system promotes the spontaneous formation of a network of capillaries and the recruitment of pericytes derived from fibroblasts. Since pericytes are essential components of the blood microvasculature, this culture system is a powerful model to study angiogenesis and endothelial cell/pericyte interactions in vitro.

Morphology and properties of pericytes

Pericytes were described in 1873 by the French scientist Charles-Marie Benjamin Rouget and were originally called Rouget cells. The Rouget cell was renamed some years later due to its anatomical location abluminal to the endothelial cell (EC) and luminal to parenchymal cells. In the brain, pericytes are located in precapillary arterioles, capillaries and postcapillary venules. They deposit elements of the basal lamina and are totally surrounded by this vascular component. Pericytes are important cellular constituents of the blood-brain barrier (BBB) and actively communicate with other cells of the neurovascular unit such as ECs, astrocytes, and neurons. Pericytes are local regulatory cells that are important for the maintenance of homeostasis and hemostasis, and are a source of adult pluripotent stem cells. Further understanding of the role played by this intriguing cell may lead to novel targeted therapies for neurovascular diseases.

Expansion of a unique macrophage subset in rheumatoid arthritis synovial lining layer

The Z39Ig protein (complement receptor for C3b and iC3b) is expressed on resident tissue macrophages in various tissues. This study was undertaken to examine the distribution of Z39Ig+cells and their phenotypic features in rheumatoid arthritis (RA) synovium, in comparison with those of osteoarthritis (OA) and psoriatic arthritis (PsA) synovium. Monoclonal anti-Z39Ig antibody was produced by immunizing Z39Ig transfected murine pre B cells and used for the identification of Z39Ig+cells. Z39Ig+cells were further stained with antibodies to macrophages, fibroblast-like synoviocytes, complement receptors and dendritic cells by using the double immunostaining method in normal, RA, OA and PsA synovium. RA synovial mononuclear cells were double-stained using anti-Z39Ig and anti-CD11c antibodies and sorted into Z39Ig+CD11c+cells and Z39Ig+CD11c-cells. These cell populations were then analysed by electron microscopy. The expression of the Z39Ig protein was limited to intimal macrophages in normal, RA, OA and PsA synovium. The numbers of Z39Ig+CD11c+cells and the ratios of Z39Ig+CD11c+cells to Z39Ig+cells were increased in the synovial lining layer of RA as compared with those of OA and PsA. The ultrastructural analysis of Z39Ig+CD11c+cells showed the character of macrophages with many secondary lysosomes and swelling of mitochondria. Z39Ig+ cells appeared to be useful for identification of resident tissue macrophages in normal synovium and the corresponding macrophages in the synovial lining layer of inflammatory arthritis. Expansion of Z39Ig+CD11c+cells was characteristic of RA synovial lining layer.