Gene expression system relative activity factor

In summary, HCMV blocks IFN-y-stimulated MHC class II transcription through two means with distinct mechanisms and kinetics. At relatively early times after infection, there is an HCMV-mediated repression of CIITA expression or function (Heise et al. 1998 LeRoy et al. 1999). At later times after infection, HCMV blocks IFN-y-stimulated transcription factor activation, CIITA expression, and class II transcription (Miller et al. 1998). The HCMV gene products mediating these effects remain to be identified however, experiments have shown that immediate-early and/or early gene products are involved (Heise et al. 1998 LeRoy et al. 1999 Miller et al. 1998). This represents a critical HCMV immunoevasive strategy as the virus has evolved two mechanisms, operative over distinct stages of the viral replication cycle, for blocking the IFN-y-inducible MHC class II transcription system. 

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