Effect of Vpx mutations on SIV replication in pigtail macaques. A) The design of the macaque infection shows that animals were inoculated by intra-rectal challenge, and one of two animals were sacrificed at 21 days after infection (✝), and the second animal in each group at 42 days after infection. Time points at which blood samples were obtained are also indicated. B) Plasma levels of SIV RNA (copies/ml) are indicated on a log scale for each of the 8 animals. The limit of detection in this assay was 50 copies/ml.