CD4 and infection: The importance of SG infection is best exemplified by numerous MCMV genes dedicated to enhancing infection of this organ, such as the virally encoded chemokine MCK-2 [31, 248–250], M116.1, which is required for mononuclear phagocyte infection [33], and M78, which facilitates MHC-II degradation and thus protects antigen-presenting cells (APCs) from CD4 T-cell control [251].