In vitro HIV-1 infection of CD4⁺ T cells derived from neonatal tissue and blood. (A) HIV-1 infection was determined using a quantitative PCR for pol proviral DNA in CD4⁺ T cells at day 3, expressed as the ratio pol/1000 copies of β-actin as a housekeeping gene. The results from blood and lymph nodes were combined in the Student t test because of their similar low levels. Gut-derived CD4⁺ T cells infected with HIV-1 contained significantly (P = .02) higher levels of pol proviral DNA than cultures with CD4⁺ T cells derived from blood or lymph nodes. PHA-stimulated adult CD4⁺ T cells from PMBC single-cell suspensions, which were used as a positive control, had comparable pol proviral DNA levels as unstimulated gut mucosa CD4⁺ T cells from fetuses and infants. (B-D) HIV-1 infection of intact infant gut explants was assessed by coexpression of viral p24 (blue) and CD45RO (brown). (B-C) p24 was colocalized with CD45RO in the newborn mucosa. (D) Control sample cultured without HIV-1. Scale bar indicates 0.1 mm.