free infection challenge assays. Representative CA NIr immunoblots of HIV-1 and SIV virions in infected cell culture supernatant samples from three independent experiments are presented. Virus and infection dilutions are labeled above the blot. Samples of the viral inocula (first lane), and supernatant samples from untreated cells (second lane) and from 14-day cultures infected at different dilutions (lanes 3–8) are presented above the blot panels. (A). Results from HIVNL43 (left) and SIVmac 239 (right), and (B) from SIVAgmTan-1.