Modulation of CXCR4 and the MHC-II associated invariant chain. (A) Jurkat T cells were transduced with HIV-1 NL4-3 Nef/eGFP constructs and assayed for surface expression of CXCR4. The range of eGFP expression used to calculate CXCR4 modulation is indicated. (B) Quantitative assessment of down-modulation of CXCR4 by the indicated Nef proteins. (C) THP-1 cells were transduced with HIV-1 NL4-3 constructs coexpressing the indicated nef alleles and GFP and assayed for surface expression of Ii. The ranges of eGFP expression used to calculate receptor modulation are indicated. (D) Quantitative assessment of SIVsmm Nef-mediated down-modulation of Ii. Values give averages ± SD derived from five independent experiments. The asterisks denote a statistical significance (P < 0.05) between HIV-1 and SIV Nef activity.