The HCMV gene products US11 and US2 differ in their ability to attack allelic forms of murine major histocompatibility complex (MHC) class I heavy chains

Human cytomegalovirus downregulates the expression of human class I major histocompatibility complex (MHC) molecules by accelerating destruction of newly synthesized class I heavy chains. The HCMV genome contains at least two genes, US11 and US2, each of which encode a product sufficient for causing the dislocation of newly synthesized class I heavy chains from the lumen of the endoplasmic reticulum to the cytosol. Based on a comparison of their abilities to degrade the murine class I molecules H-2K(b), K-d, D-b, D-d, and L(d), the US11 and US2 gene products have non-identical specificities for class I molecules. Specifically, in human astrocytoma cells (U373-MG) transfected with the US11 gene, the K-b, D-b, D-d, and L(d) molecules expressed via recombinant vaccinia virus are rapidly degraded, whereas in US2-transfected cells, only D-b and D-d are significantly destabilized. The diversity in HCMV-encoded functions that interfere with class I-restricted presentation likely evolved in response to the polymorphism of the MHC.