Endothelial expression of PD‐L1 and PD‐L2 down‐regulates CD8⁺ T cell activation and cytolysis

Abstract

Interactions between CD8+ T cells and endothelial cells are important in both protective and pathologic immune responses. Endothelial cells regulate the recruitment of CD8 + T cells into tissues, and the activation of CD8 + T cells by antigen presentation and costimulatory signals. PD-L1 and PD-L2 are recently described B7-family molecules which bind to PD-1 on activated lymphocytes and down-regulate T cell activation. We found that PD-L1 is expressed on interferon-+ stimulated cultured human and mouse endothelial cells, while PD-L2 was found on stimulated human but not mouse endothelial cells. Expression was further upregulated by TNF- § . Antibody blockade of endothelial cell PD-L1 and PD-L2 enhanced endothelial cell costimulation of PHA-activated human CD8 + T cells. Antibody blockade of mouse endothelial cell PD-L1 enhanced both IFN-+ secretion and cytolytic activity of CD8 + T cells in response to endothelial cell antigen presentation. These results show that IFN-+ activated endothelial cells can inhibit T cell activation via expression of the immunoinhibitory PD-L1 and PD-L2 molecules. Endothelial expression of PD-ligands would allow activation and extravasation of T cells without excessive vessel damage. Our findings highlight a potentially important pathway by which endothelial cells down-regulate CD8 + T cellmediated immune responses.

A Novel Function for Programmed Death Ligand-1

“…22 Briefly, tissue from 9-to 15-day-old mice was digested with type-1 collagenase (Worthington Biochemical, Lakewood, NJ), mechanically dissociated, passed through a 70-m filter, spun, resuspended, and incubated with sheep anti-rat Dynal beads (Invitrogen) that were coated with rat antimouse CD31 (clone MEC13.3; BD Biosciences, San Diego, CA). Cells were magnetically selected and plated on fibronectin-coated (Invitrogen) tissue culture dishes in RPMI complete media supplemented with 100 g/mL endothelial mitogen (Endothelial cell growth supplement; Biomedical Technologies, Stoughton, MA).…”

PD-1:PD-L1 Interactions Contribute to the Functional Suppression of Virus-Specific CD8+ T Lymphocytes in the Liver

“…PD-1 has two known ligands: PD ligand (PD-L)1 (B7-H1) and PD-L2 (B7-DC). PD-L1 is expressed in a wide variety of tissues and by a number of different cell types, and its expression is upregulated by IFN-␥ (13)(14)(15)(16)(17)(18)(19). The expression of PD-L2 is much more restricted and appears to be limited to a subset of bone marrow-derived cells, including dendritic cells and macrophages (15,20).…”

“…The PD-L1 blocking Ab 10F.9G2 (rat IgG2b) has been previously described (19,35). HBV transgenic recipients were injected i.p.…”

“…IFN-␥ mediates up-regulation of PD-L1 on a variety of cell types (19,20). To determine whether IFN-␥ produced by CTLs is responsible for the up-regulation of PD-L1 on hepatocytes, we treated MMDH3 cells, an immortalized murine hepatocyte cell line, with culture medium conditioned by peptide-stimulated HBV-specific CTLs.…”

Modulating Co-Stimulation

“…PDL-1 has also been detected in nonlymphoid organs in both mice and humans. 69,70 The engagement of PD-1, with its ligand PDL-1, causes inhibition of anti-CD3-induced activation of T cells particularly in suboptimal co-stimulatory condition and when weak signals are provided to the TCR. 71 The engagement of PDL-2 is also capable of reducing CD4ϩ T-cell activation and cytokine production after TCR stimulation.…”