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

J Neuroinflammation. 2011 Nov 8;8:155. doi: 10.1186/1742-2094-8-155.

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 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • B7-H1 Antigen / genetics
  • B7-H1 Antigen / metabolism*
  • Blood-Brain Barrier / cytology*
  • Blood-Brain Barrier / immunology
  • Blood-Brain Barrier / pathology
  • Brain / blood supply
  • Brain / cytology
  • Brain / immunology
  • CD4-Positive T-Lymphocytes / immunology
  • CD8-Positive T-Lymphocytes / cytology
  • CD8-Positive T-Lymphocytes / immunology*
  • Cell Proliferation
  • Cells, Cultured
  • Coculture Techniques
  • Cytokines / immunology
  • Endothelial Cells / cytology
  • Endothelial Cells / immunology*
  • Female
  • Humans
  • Lymphocyte Activation / immunology
  • Male
  • Middle Aged
  • Multiple Sclerosis / immunology*
  • Multiple Sclerosis / pathology*
  • Programmed Cell Death 1 Ligand 2 Protein / genetics
  • Programmed Cell Death 1 Ligand 2 Protein / metabolism*
  • Programmed Cell Death 1 Receptor / metabolism
  • Transendothelial and Transepithelial Migration

Substances

  • B7-H1 Antigen
  • CD274 protein, human
  • Cytokines
  • PDCD1 protein, human
  • PDCD1LG2 protein, human
  • Programmed Cell Death 1 Ligand 2 Protein
  • Programmed Cell Death 1 Receptor