CD80 and viral infectious disease: Cryo-EM further revealed that the interaction between M2 and B7.1 can also induce conformational changes in B7.1, enhancing its affinity for the inhibitory ligand PD-L1, forming a “double brake” that further suppresses the immune synapse; finally, functional validation: gene deletion experiments showed that the virulence of the M2-deficient strain was significantly reduced in primate models, suggesting that this mechanism is essential for sustained viral infection in vivo [13].