858 Early and Late Barriers in Productive Human Immunodeficiency Virus Type 1 Infection of Trophoblast Cells Are Overcome by the Pro-Inflammatory Cytokines IL-1 and TNF-alpha: Possible Implications for the Mechanism of In Utero Transmission of HIV-1 G. Vidricaire*, M. J. Tremblay Univ Laval, Ste-Foy, Canada
Background: Maternal-infant transmission of HIV-1 is the primary cause of this retrovirus infection in neonates. However, how HIV-1 crosses the placenta to reach the fetus remains undefined. This presentation addresses the mechanism of HIV-1 biology in trophoblasts.
Methods:Trophoblastic cell lines were infected with reporter HIV-1 particles pseudotyped with VSV-G, HIV-1 macrophage and T-tropic envelopes and with fully infectious HIV-1 virions. The cells were exposed post-infection to growth factors and cytokines present in the vicinity of trophoblastic cells during gestation. Transcriptional activity and viral production were monitored. Molecular constructs of the LTR subtypes were tested. Molecular events leading to the cytokine-induced transactivation were assessed with expression vectors mutated at the NF-kappaB-binding sites within the HIV-1 LTR.
Results: In the absence of external stimulus, trophoblastic lines produced weak viral transcription upon infection with virus bearing HIV-1’s envelope but high viral transcription upon infection with the VSV-G pseudotype. Thus, failure of HIV-1 to productively infect trophoblasts occurs through a block early in its life cycle. Treating the cells with TNF-alpha and IL-1 post-infection resulted in higher HIV-1 LTR-driven transcriptional activity in trophoblast cells infected not only with HIV-1 particles pseudotyped with VSV-G but also with viruses bearing HIV-1 envelopes. Experiments conducted with infectious HIV-1 indicate that another block at a later stage in the infection cycle is also present in trophoblasts since a treatment with TNF-alpha and a co-culture step with indicator cells are necessary in order to detect production of fully competent viruses. The effect mediated by TNF-alpha and IL-1 on the LTR activity was neither cell line- nor clade-specific and is induced via NF-kappaB.
Conclusions:These data demonstrate for the first time that the natural low permissiveness of trophoblasts to productive HIV-1 infection can be overcome with physiologic doses of TNF-alpha and IL-1, which are both expressed by the placenta. Considering that there is a linear correlation between viral load and HIV-1 vertical transmission, the environmental milieu may thus contribute to the propagation of HIV-1 across the placenta.
