PLMCs isolated from infected placentas harbor infectious HIV virions within MVBs. (A) TEM imaging of PLMCs isolated from HIV⁺ women at term showed cytoplasmic MVBs (white box) containing (B) apparent 90-nm diameter HIV virions with typical nucleocapsid core particles (indicated by arrow). (C) DNA from IgE-biotin–selected PLMCs isolated from HIV⁺ women at term showed detectable levels of integrated HIV proviral DNA by PCR. (D) IgE-biotin–selected PLMCs isolated from HIV⁺ women at term and cultured in the presence of SA (to induce IgE cross-linking–mediated PLMC activation) release infectious virus that is able to infect (allo-) activated cord blood (CB) mononuclear cells. CB1 and CB2 represent 2 independent cord blood samples collected from HIV⁻ fetal donors; allo, γ-irradiated allogeneic PBMCs stimulator cells;CBUI1 and CBUI2, results from uninfected CB cells. (E) IgE-biotin–selected PLMCs isolated from HIV⁺ women at term and cultured in the presence of SA released significant levels of HIV-p24⁺ virus (by day 6 after activation) that was used to infect susceptible LAD-2 MCs. Elevated levels of HIV-p24 (∼ 145 pg/mL) were detected in culture supernatant fluids of infected LAD-2 at day 7 after infection. All experiments were performed a minimum of 3 times. All error bars represent standard deviation of the mean of replicate PCR reactions at each data point.