FIG. 6.
HT1080 cells (5 × 105 cells/ml) were infected or not with HPIV3 (MOI of 1.0) and IFN-γ (100 U/ml) either alone or together and harvested at 72 h postinfection for MHC class II assay. Shown is the model for HPIV3-mediated inhibition of IFN-γ-induced MHC class II expression. The inhibition occurs by targeting two distinct steps of the IFN-γ-induced MHC class II expression pathway. Step 1 represents CIITA mRNA accumulation directly targeted by HPIV3 gene products for down-regulation. Step 2 represents a step(s) downstream of the CIITA mRNA accumulation targeted for inhibition by IFN-α/β present in the infected cell culture supernatant.