Vaginal secretions may help HIV-1 transmission to women by increasing infectivity for CD4+ cells and allowing entrance into some CD4-epithelial cells.

The cell source of prolonged production of human immunodeficiency virus type 1 (HIV-1) in breast milk (8, 11, 21-23, 26, 27, 29) is not yet clear, since lymphocyte counts in milk decline rapidly after delivery (15). The risk of mother-to-child transmission through breast-feeding has been reemphasized recently, when discontinuation of antiretroviral therapy was followed by an increase in HIV-1 RNA load (10, 13). Therapy withdrawal in a mother after childbirth might also increase viral load in milk, although a short course of oral zidovudine during the peripartum period provided an important protection of the child despite breast-feeding (7).We have previously shown (12) that HIV-1 variants incubated in vaginal wash samples showed increased infectivity for lymphocyte cultures and acquired the ability to grow in a CD4-negative epithelial cell line obtained from a cervical epidermoid carcinoma. This effect was attributed to cathepsin D, which we purified from vaginal secretions. This protease might react with the viral gp120 and modify affinities for coreceptors.In the present work, we found that human breast milk also enhanced the infectivity of some HIV-1 variants. Two experiments showed that the enhancing factor was susceptible to cathepsin D inhibitors.Enhancing effect of milk is destroyed by inhibitors of cathepsin D. To demonstrate the effect of pepstatin A, an experiment was run in two steps. Milk sample 2 or buffer was first preincubated for 10 min at 37°C with 20 g of pepstatin A per ml or with buffer, and these mixtures were further incubated with HIV-1 variants before inoculation into primary lymphocyte cultures. Milk preincubated with pepstatin A lost its enhancing effect on HIV-1 IIIb, but enhancement was not completely lost when the same milk sample was assayed on fresh syncytium-inducing isolates (SI), 492 isolates, or non-syncytium-inducing isolates (NSI), 75 isolates (Fig. 1). Chymotrypsin and trypsin inhibitors did not modify the enhancing effect (not shown). A similar experimental protocol was applied to study the effect of a polyclonal anti-cathepsin D antibody on enhancing properties of milk, vaginal wash, or cathepsin D (Table 1).Enhancement of SI 121 and NSI 114 isolates was decreased by treatment with the anti-cathepsin D antibody, although it was not completely abolished in some of the mixtures. Table 2 summarizes data obtained in various experiments and shows that the enhancement effect of milk sample 2 on the three isolates simultaneously tested was greater than that of milk sample 1, although this difference did not appear in the assay of the laboratory strain, HIV-1 IIIb. A survey of the whole table does not disclose a general trend distinguishing a difference between SI and NSI isolates regarding their susceptibility to milk enhancement. This table also shows the effect of various concentrations of milk sample 2. It was striking that the final dilution of 1:2 showed a lower enhancing effect than did the dilution of 1:10. At higher concentrations, there may be a balance with HIV-1 inhi...

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In vitro incubation of human cytomegalovirus (Towne strain) with 8 U/ml human recombinant myeloperoxidase plus sodium chloride and glucose nearly abolished viral infectivity. To assay the effect on intracellular infection, cell toxicity of the enzymes was first studied. Even the high dose of 16 U/ml of recombinant myeloperoxidase plus 10 mU/ml glucose oxidase did not decrease MRC5 cell growth. By contrast, this dose reduced proliferation of activated THP1 cells. Even half of the myeloperoxidase dose proved slightly toxic to these cells. Non-cytotoxic concentrations of the reagents were used to monitor their effect on cytomegalovirus infection. In MRC5 cells, even the low dose of 4 U/ml myeloperoxidase plus glucose oxidase inhibited synthesis of cytomegalovirus early antigens, as tested by immunofluorescence. Viral release in the supernatant was decreased by 4 logs. In THP1 cells, which produce endogenously hydrogen peroxide, myeloperoxidase alone (8 U/ml) decreased the formation of early and late antigens by 53 and 44%, respectively.

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