MCMV degrades MHC II.

<p><b>a</b>. RAW-C2TA cells infected with MCMV-GFP (0.5 p.f.u. / cell, 48h) were analysed for surface MHC II by flow cytometry. Mean fluorescence intensity was >10-fold lower on GFP⁺ cells than on GFP^-. CD44 and CD71 mean fluorescence intensity of GFP⁺ cells was reduced <2-fold. Numbers show % cells in each quadrant. Each data set represents at least 3 experiments. <b>b</b>. RAW-C2TA cells were uninfected or infected with MCMV-βgal (1 p.f.u. / cell, 72h), then fixed, permeabilized and stained for βgal and MHC II. White arrows show example MHC II^- infected cells; dark grey arrows show MHC II⁺ uninfected cells in the same cultures; light grey arrows show weakly βgal⁺ cells with MHC II in internal vesicles. Significantly fewer MCMV⁺ cells (<10%, n>200) than MCMV^- cells (>90%, n>200) were MHC II⁺ (p<10^-4 by Fisher's exact test). >100 weakly βgal⁺ cells showed MHC II redistribution. <b>c</b>. RAW-C2TA cells were infected as in <b>b</b>. MHC II⁺ cells were identified with conformation-dependent (M5/114) and -independent (IBL5/22) antibodies. Arrows show example infected cells. Significantly fewer GFP⁺ (<15%, n>100) than GFP^- cells (>90%, n>100) were M5/114⁺ and IBL5/22⁺ (p<10^-4 by Fisher's exact test). <b>d</b>. Peritoneal macrophages were recovered from BALB/c or C57BL/6 mice 72h after i.p. thiglycollate. Non-adherent cells were discarded. The remaining cells were infected or not with MCMV-GFP (1 p.f.u. / cell, based on total cell numbers before adherence). 48h later surface MHC II and CD44 were analysed by flow cytometry. Numbers show % total cells in each quadrant, collecting >5000 cells. In uninfected cultures, macrophages were 22% (BALB/c) and 26% (C57BL/6) MHC II⁺. In infected cultures, GFP^- macrophages were 27% (BALB/c) and 24% (C57BL/6) MHC II⁺, while GFP⁺ macrophages were 0.3% (BALB/c) and 0.2% (C57BL/6) MHC II⁺ (p<10^-4 by X² test).