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Updated: May 25, 2026

Immunohistochemical Staining of B7-H1 (PD-L1) on Paraffin-embedded Slides of Pancreatic Adenocarcinoma Tissue
Published on: January 3, 2013
The PD-1/PD-L1 pathway in human pathology
M Saresella1, V Rainone, N M Al-Daghri
1Don C Gnocchi Foundation, ONLUS, Milan, Italy.
T-cell activation is dependent on signals delivered through the antigen-specific T-cell receptor and accessory receptors on T-cells. Integration of signals through this family of costimulatory and inhibitory receptors and their ligands regulates the balance between T-cell activation, tolerance, and immunopathology. Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, deliver inhibitory signals and exert a vital and diverse range of immunoregulatory roles in T-cell activation, tolerance, and immune-mediated tissue damage. In this review, we revisit current understanding of the immunoregulatory functions of PD-1 and its ligands and their involvement in immune-mediated diseases.
T-cell activation is dependent on signals delivered through the antigen-specific T-cell receptor and accessory receptors on T-cells. Integration of signals through this family of costimulatory and inhibitory receptors and their ligands regulates the balance between T-cell activation, tolerance, and immunopathology. Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, deliver inhibitory signals and exert a vital and diverse range of immunoregulatory roles in T-cell activation, tolerance, and immune-mediated tissue damage. In this review, we revisit current understanding of the immunoregulatory functions of PD-1 and its ligands and their involvement in immune-mediated diseases.
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