Effect of primary HIV-1 and HIV-2 Nef proteins on surface receptor expression. Jurkat CD4-CCR5 cells were transduced with retroviral vectors expressing the indicated nef alleles and eGFP (Nef-IRES-eGFP) and were analyzed by flow cytometry. (A and C) Bivariate dot plots show expression of CD4, MHC-I, CXCR4 as a function of eGFP (Nef) expression. Dot plots shown are representative of results obtained in at least 3 independent experiments. (B and D) To determine relative CD4, MHC-I and CXCR4 surface levels, the MFI of transduced cells (eGFP+) was divided by the MFI of untransduced cells (eGFP-) in the same culture. Data represent the mean relative expression and standard deviations from at least 3 independent experiments. eGFP represents the value for control transduced cells expressing only the marker gene but no Nef. An asterisk (*) over a bar indicates a statistically significant difference between the experimental construct compared with the eGFP control (P < 0.01).