. 2021 Jan 20;9(2):98. doi: 10.3390/biomedicines9020098

Table 2.

Comparison of immune checkpoints.

	PD-1	CTLA-4
Expression on cells	Activated B and T cells Activated NK cells (natural killers) Tumor infiltrating lymphocytes (TILs) in various types of cancer	Effector and regulatory T cells activated in the initial phase of antigen response
Function	Inhibitory receptor Reduces the activity of T cells in peripheral tissues after an inflammatory reaction occurs Reduces the autoreactivity of lymphocytes and NK cells	Inhibitory receptor Regulates (reduces) the activation of T cells at an early stage of their differentiation
Ligands	PD-L1 (B7-H1/CD274) PD-L2 (B7-CD/CD273)	CD80 (B7.1) CD86 (B7.2)
Mechanism desciption	The interaction of the receptor with its ligand causes the activation of Src homology region 2 domain-containing phosphatase-2 (SHP-2) and a decrease in the expression of the Bcl-xL protein, which results in the inhibition of the activity of PI3K/AKT kinase	The interaction of the receptor with its ligand causes the activation of SHP-2 and proteine phosphatase 2 (PPA2) and the blockade of the expression of various proteins in the cell membrane and the flow of Ca²⁺ ions, which results in the inhibition of signal transmission by T-cell receptor (TCR) (blockade of ZAP70 protein formation)