The concentrations of the HIV-1 p24 protein upon stimulation by IFN-γ and infection by Nef-competent virus (HIV-1 NL4-3) or Nef-deficient virus (HIV-1 NL4-3ΔNef) were determined in lysates of CD4+ Jurkat cells by enzyme-linked immunosorbent assay (ELISA). This evidence concerns the gene CD4 and infection.