Potential interaction involving PD-1/PD-L1 between receptors and ligands on lymphoma cells, professional antigen-presenting cells (APCs), and T cells. PD-1–PD-L1 interactions are highlighted in red. Functional consequences of the interaction are denoted by “+” (stimulatory) and “–” (inhibitory) signs. The “+/–“ signs indicate context-dependent effects of PD-L1–CD80 interaction on T cells. For PD-1 expression on malignant B cells in some non-Hodgkin B-cell lymphomas, PD-1 ligands and functions are currently unclear (indicated by “?”). TCR, T-cell receptor.