Quantification and Statistical Analysis

In all experiments, data are presented as mean ± SEM unless stated otherwise. Statistical tests were selected based on appropriate assumptions with respect to data distribution and variance characteristics. The number of biological replicates and mice is defined in the figure legends. The statistical analysis used for the identification of the PD-1 and BTLA high-confidence interactors is developed in the paragraph ‘Filtering strategy for the identification of the PD-1 and BTLA high-confidence interactomes’.