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Human brain endothelial cells endeavor to immunoregulate CD8 T cells via PD-1 ligand expression in multiple sclerosis

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Description

Multiple sclerosis (MS), an inflammatory disease of the central nervous system (CNS), is characterized by blood-brain barrier (BBB) disruption and massive infiltration of activated immune cells. Engagement of programmed cell death-1 (PD-1) expressed on activated T cells with its ligands (PD-L1 and PD-L2) suppresses T cell responses. We recently demonstrated in MS lesions elevated PD-L1 expression by glial cells and absence of PD-1 on many infiltrating CD8 T cells. We have now investigated whether human brain endothelial cells (HBECs), which maintain the BBB, can express PD-L1 or PD-L2 and thereby modulate T cells. Methods We used primary cultures of HBECs isolated from non-tumoral CNS tissue either under basal or inflamed conditions. We assessed the expression of PD-L1 and PD-L2 using qPCR and flow cytometry. Human CD8 T cells were isolated from peripheral blood of healthy donors and co-cultured with HBECs. Following co-culture with HBECs, proliferation and cytokine production by human CD8 T cells were measured by flow cytometry whereas transmigration was determined using a well established in vitro model of the BBB. The functional impact of PD-L1 and PD-L2 provided by HBECs was determined using blocking antibodies. We performed immunohistochemistry for the detection of PD-L1 or PD-L2 concurrently with caveolin-1 (a cell specific marker for endothelial cells) on post-mortem human brain tissues obtained from MS patients and normal controls. Results Under basal culture conditions, PD-L2 is expressed on HBECs, whilst PD-L1 is not detected. Both ligands are up-regulated under inflammatory conditions. Blocking PD-L1 and PD-L2 leads to increased transmigration and enhanced responses by human CD8 T cells in co-culture assays. Similarly, PD-L1 and PD-L2 blockade significantly increases CD4 T cell transmigration. Brain endothelium in normal tissues and MS lesions does not express detectable PD-L1; in contrast, all blood vessels in normal brain tissues are PD-L2-positive, while only about 50% express PD-L2 in MS lesions. Conclusions Our observations suggest that brain endothelial cells contribute to control T cell transmigration into the CNS and immune responses via PD-L2 expression. However, such impact is impaired in MS lesions due to downregulation of endothelium PD-L2 levels.

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Publié par
Publié le 01 janvier 2011
Nombre de lectures 13
Langue English
Poids de l'ouvrage 6 Mo
Pittetet al.Journal of Neuroinflammation2011,8:155 http://www.jneuroinflammation.com/content/8/1/155
JOURNAL OF NEUROINFLAMMATION
R E S E A R C HOpen Access Human brain endothelial cells endeavor to immunoregulate CD8 T cells via PD1 ligand expression in multiple sclerosis 1 21,3 1* Camille L Pittet , Jia Newcombe , Alexandre Pratand Nathalie Arbour
Abstract Background:Multiple sclerosis (MS), an inflammatory disease of the central nervous system (CNS), is characterized by bloodbrain barrier (BBB) disruption and massive infiltration of activated immune cells. Engagement of programmed cell death1 (PD1) expressed on activated T cells with its ligands (PDL1 and PDL2) suppresses T cell responses. We recently demonstrated in MS lesions elevated PDL1 expression by glial cells and absence of PD1 on many infiltrating CD8 T cells. We have now investigated whether human brain endothelial cells (HBECs), which maintain the BBB, can express PDL1 or PDL2 and thereby modulate T cells. Methods:We used primary cultures of HBECs isolated from nontumoral CNS tissue either under basal or inflamed conditions. We assessed the expression of PDL1 and PDL2 using qPCR and flow cytometry. Human CD8 T cells were isolated from peripheral blood of healthy donors and cocultured with HBECs. Following coculture with HBECs, proliferation and cytokine production by human CD8 T cells were measured by flow cytometry whereas transmigration was determined using a well establishedin vitromodel of the BBB. The functional impact of PDL1 and PDL2 provided by HBECs was determined using blocking antibodies. We performed immunohistochemistry for the detection of PDL1 or PDL2 concurrently with caveolin1 (a cell specific marker for endothelial cells) on postmortem human brain tissues obtained from MS patients and normal controls. Results:Under basal culture conditions, PDL2 is expressed on HBECs, whilst PDL1 is not detected. Both ligands are upregulated under inflammatory conditions. Blocking PDL1 and PDL2 leads to increased transmigration and enhanced responses by human CD8 T cells in coculture assays. Similarly, PDL1 and PDL2 blockade significantly increases CD4 T cell transmigration. Brain endothelium in normal tissues and MS lesions does not express detectable PDL1; in contrast, all blood vessels in normal brain tissues are PDL2positive, while only about 50% express PDL2 in MS lesions. Conclusions:Our observations suggest that brain endothelial cells contribute to control T cell transmigration into the CNS and immune responses via PDL2 expression. However, such impact is impaired in MS lesions due to downregulation of endothelium PDL2 levels. Keywords:bloodbrain barrier, CD8 T cells, endothelial cells, PDL1, PDL2, B7 molecules
Background Multiple sclerosis (MS) is an inflammatory disorder of the central nervous system (CNS), pathologically charac terized by focal demyelination, neuronal damage, glial cell activation and massive infiltration of immune cells
* Correspondence: nathalie.arbour@umontreal.ca 1 Department of Medicine, Université de Montréal, CRCHUM, Pavilion J.A. de Sève, 1560 Sherbrooke E, Montreal, QC, H2L 4M1, Canada Full list of author information is available at the end of the article
[1]. Under physiological conditions, the bloodbrain bar rier (BBB) restricts and regulates the entrance of pro teins, nutrients and cells from the periphery to the CNS [2,3]. However, during MS pathogenesis, the BBB impairment facilitates the infiltration of peripheral immune cells into the CNS [1]. Infiltrating cells detected within MS lesions include macrophages and T cells. Although CD4 T cells have been established as impor tant players in MS pathogenesis, CD8 T cells are
© 2011 Pittet et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.