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18 The Initial Attachment and Penetration of HIV-1 into the Vaginal Mucosa Occurs Independently of the Viral gp120 Glycoprotein
H. Liu1, L. Lai1, Y. Jia1, A. Tousson1, J. C. Kappes1,2, and X. Wu*1
1Univ. of Alabama at Birmingham, USA and 2Med. Res. Service, Dept. of Veterans Affairs, Birmingham, AL, USA
Background: HIV-1 infection continues to spread globally, predominantly by heterosexual contact. Rational prophylactic strategies to control HIV transmission rely upon a detailed cellular and molecular understanding of the initial interactions between HIV and the host. Although advances have been made to identify the kinds of cell that are first infected, little progress has been made to delineate the earliest interaction(s) of HIV virions with the mucosal epithelium. This is due in great measure to the lack of experimental methods with sufficient sensitivity and specificity to analyze the interaction of infectious virions with the mucosa in vivo.
Methods: We have pioneered the use of HIV/SIV accessory protein (Vpr and Vpx) for incorporating both viral and nonviral proteins into HIV virion by their expression in trans as heterologous fusion molecules. Here, we show the packaging of Vpr-GFP. Importantly, the GFP-containing virions are infectious and can be directly visualized by fluorescent microscopy. This enabled a unique and quantitative approach to analyze the very earliest cellular, viral, and molecular interactions that occur during mucosal HIV-1 transmission.
Results: Our data show that efficient attachment of HIV-1 to human and nonhuman cell lines occurs independently of viral gp120 but requires cell surface heparan sulfate. Moreover, wild-type and gp120-minus viruses bind with equal efficiency to both human macrophages and primary stratified epithelial cells. This binding is blocked by soluble heparin. Using a mouse model, we demonstrated that both wild-type and gp120-minus HIV-1 efficiently bind to the vaginal mucosal surface. These GFP virions were found to penetrate into the mucosa. Pretreatment of GFP virions with heparin dramatically decreased binding and penetration.
Conclusions: These data, for the first time, provide the direct evidence that HIV interacts with epithelial cell and the vaginal mucosal surface through a gp120-indepedent pathway. Our data suggest a role of mucosal heparan in HIV-1 transmission. The visualization of infectious GFP-labeled virions provides a useful tool to study HIV-1 mucosal transmission in vivo.
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