1. Figure 1 Postulated mechanisms of action of PD‑1, PD‑L1 and PD‑L2
Figure 1 | Postulated mechanisms of action of PD-1, PD-L1 and PD-L2. Programmed cell death receptor 1 (PD-1) can be expressed by T cells, natural killer cells, B cells and some myeloid cells. On T cells, PD-1 functions as an immune checkpoint. Binding of its ligands PD-L1 and PD-L2, which are also transmembrane proteins, results in downregulation of T-cell-mediated immune responses. PD-L1 is constitutively expressed on several types of immune cells and at low levels on various nonhaematopoietic cells, in which its expression can be induced by various stimuli. PD-L2 is expressed on fewer cell types, including some antigen-presenting cells. Tumour cells can express PD-L1 to evade immunosurveillance and interaction with PD-1 on tumour-infiltrating T cells leads to inhibition of T-cell function. Furthermore, reverse signalling through PD-L1 can make tumour cells refractory to cytotoxic T-cell lysis. Figure adapted from Ref. 142, Macmillan Publishers Limited.
Figure adapted from Nguyen, L. T. & Ohashi, P. S. Clinical blockade of PD1
and LAG3 — potential mechanisms of action. Nat. Rev. Immunol. 15, 45–56 (2015), Macmillan Publishers Limited.
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