NGF-mediated signaling involved in the enhancement of HIV-1 production. Macrophages were infected with an R5-tropic HIV-1 isolate (Ba-L), and 13 to 14 days after infection cells were treated with K252a (A) or the indicated pharmacologic modulators (B) 15 minutes before NGF (10 ng/mL) addition. These cells were kept in culture for an additional 2 days, when virus replication was measured in the culture supernatant by an HIV-1 p24 ELISA. Data represent means ± SEM of 4 independent experiments. Virus production in the positive control (HIV-infected cells cultured only with medium): 232 ± 51 of ng/mL p24 Ag. ¥P < .05 for HIV-1–infected cells treated or not with the pharmacologic inhibitors; *P < .05 for HIV-1–infected cells treated or not with NGF; #P < .05 for HIV-1–infected and NGF-boosted cells treated or not with the pharmacologic inhibitors.