Twenty-four-hour post-infection, total RNA was analysed for MIP-1α expression by real-time PCR. (G and H) U937 cells (5 × 107) were transfected with siRNA Tat or siRNA control (2 nmol), or left untransfected; 24 h later, cells were infected with HXB2-pseudotyped NL4-3.FLAG-Tat.R−E− virions, or left uninfected.