PD-1 signaling
Fife BT, Bluestone JA. Control of peripheral T-cell tolerance and autoimmunity via the CTLA-4 and PD-1 pathways. Immunol Rev. 2008 Aug;224():166–82. doi: 10.1111/j.1600-065x.2008.00662.x. PMID: 18759926.; Keir ME, Butte MJ, Freeman GJ, Sharpe AH. PD-1 and Its Ligands in Tolerance and Immunity. Annu. Rev. Immunol. 2008 Apr 01;26(1):677–704. doi: 10.1146/annurev.immunol.26.021607.090331.