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Replication of the human immunodeficiency virus type 1 (HIV-1) isolate MN in CEM cells was less neutralized by the plasma from the mothers of infected children (MIC) in comparison with the plasma from the mothers of uninfected children (MUC). Significantly higher neutralization titres were observed for the sera from MUCs compared with MICs, and only the sera from MUC showed 100% neutralization of the HIV-1 MN strain. We suggest that a simple neutralization assay as described here could be useful in prognostic analyses.

Neutralization analyses were carried out with plasma from 132 volunteer human immunodeficiency virus (HIV)-1 infected women (76% pregnant, 24% with infants suspected for HIV-1 infection) collected between 1994 and 1998, against autologous and heterologous primary- and the reference HIV-1 MN isolates. A significantly lower percentage of HIV-1 transmissions was observed after 1996, parallel to a more intense antiretroviral treatment of infected pregnant women. HIV-1 isolation was significantly more frequent from peripheral blood mononuclear cells of mothers of infected children than mothers of uninfected children (P = 0.0065). Neutralization of autologous HIV-1 isolates was comparable for HIV-1 transmitters and nontransmitters' plasma, whereas neutralization of the reference isolate HIV-1 MN was more frequent at high titers for pregnant women who did not transmit HIV to their offspring compared to pregnant women who did. Although neutralization of heterologous primary HIV-1 isolates from HIV transmitters and non transmitters by transmitter plasma occurred with similar frequency, neutralization of isolates from transmitters was much more frequent when heterologous plasma from nontransmitters were used. Macrophage-tropic heterologous HIV-1 isolates were neutralized more frequently at higher titers by plasma from nontransmitters than from transmitters. The results obtained indicate that antiretroviral treatment, lack of success of HIV-1 isolation and high titers of antibodies able to neutralize macrophage-tropic viruses appear to be of importance for protection against HIV-1 vertical transmission for the group of patients studied.