Loss of inducible virus in CD45RA naive cells after human immunodeficiency virus-1 entry accounts for preferential viral replication in CD45RO memory cells

Controversy exists concerning the preferential infection and replication of human immunodeficiency virus-1 (HIV-1) within naive (CD45RA⁺) and memory (CD45RO⁺) subsets of CD4⁺ lymphecytes. To explore the susceptibility of these subsets to HIV-1 infection, we purified CD45RA⁺/CD4+ (RA) and CD45RO⁺CD4⁺ (RO) cells from normal donors and subjected them to a novel monokine activation culture scheme. Following HIV-1 infection and interleukin-2 (IL-2) induction, viral production measured on day 13 was 19- fold greater in Re cultures compared with RA cultures. IL-2-stimulated proliferation in uninfected control cultures was equivalent. To explore the mechanisms by which RA cells were reduced in viral production capacity, RA and RO cells were exposed to HIV-1 followed by treatment with trypsin, and then phytohemagglutinin antigen (PHA)-stimulated at days 4, 7, and 10 postinfection. HIV-1 production in day 4 postinfection RA and Re cultures was analogous, indicating that viral fusion and entry had occurred in both cell types. However, whereas similarly treated day 7 and 10 postinfection Re cultures produced virus, HIV-1 was markedly reduced or lost in the corresponding RA cultures. These results suggest that a temporally labile postfusion HIV-1 complex exists in unstimulated RA cells that requires cellular activation signals beyond that provided by IL-2 alone for productive infection.