A 60-year-old immunosuppressed renal transplant recipient presents with fever, pneumonitis, and low CD4 count. Bronchoscopy shows cytomegalic cells with owl-eye intranuclear inclusions. What specific cellular mechanism does CMV exploit to downregulate MHC I and evade CD8+ T-cell recognition?

• A CMV ICP47 equivalent blocks TAP transporter
• B CMV encodes viral IL-10 to downregulate all MHC expression
• C CMV glycoprotein B binds beta-2-microglobulin preventing MHC I assembly
• D CMV US11 and US2 proteins redirect MHC I heavy chains to the proteasome for degradation ✓

Explanation

CMV encodes multiple immune evasion proteins. US11 and US2 are ER-localised glycoproteins that specifically bind MHC class I heavy chains and redirect them for retrotranslocation and proteasomal degradation (dislocation), preventing MHC I surface expression and CD8+ T-cell recognition. US3 retains MHC I in the ER. US6 inhibits TAP peptide transporter (analogous to HSV ICP47). CMV does encode viral IL-10 (cmvIL-10) which downregulates MHC II (not I) on APCs. The dual strategy of downregulating MHC I (avoiding CD8+ T cells) while retaining HLA-E/C to avoid NK-cell killing (via UL18 as MHC I decoy) makes CMV a master immune evader.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.