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Updated: Aug 26, 2026
Assessment of Immunologically Relevant Dynamic Tertiary Structural Features of the HIV-1 V3 Loop Crown R2 Sequence by ab initio Folding
Published on: September 15, 2010
Differential CD4/CCR5 utilization, gp120 conformation, and neutralization sensitivity between envelopes from a
J Martín1, C C LaBranche, F González-Scarano
1Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Abstract:
Human immunodeficiency virus type 1 (HIV-1) infects and induces syncytium formation in microglial cells from the central nervous system (CNS). A primary isolate (HIV-1(BORI)) was sequentially passaged in cultured microglia, and the isolate recovered (HIV-1(BORI-15)) showed high levels of fusion and replicated more efficiently in microglia (J. M. Strizki, A. V. Albright, H. Sheng, M. O'Connor, L. Perrin, and F. González-Scarano, J. Virol. 70:7654-7662, 1996). The parent and adapted viruses used CCR5 as coreceptor. Recombinant viruses demonstrated that the syncytium-inducing phenotype was associated with four amino acid differences in the V1/V2 region of the viral gp120 (J. T. C. Shieh, J. Martin, G. Baltuch, M. H. Malim, and F. González-Scarano, J. Virol. 74:693-701, 2000). We produced luciferase-reporter, env-pseudotyped viruses using plasmids containing env sequences from HIV-1(BORI), HIV-1(BORI-15), and the V1/V2 region of HIV-1(BORI-15) in the context of HIV-1(BORI) env (named rBORI, rB15, and rV1V2, respectively). The pseudotypes were used to infect cells expressing various amounts of CD4 and CCR5 on the surface. In contrast to the parent recombinant, the rB15 and rV1V2 pseudotypes retained their infectability in cells expressing low levels of CD4 independent of the levels of CCR5, and they infected cells expressing CD4 with a chimeric coreceptor containing the third extracellular loop of CCR2b in the context of CCR5 or a CCR5 Delta4 amino-terminal deletion mutant. The VH-rB15 and VH-rV1V2 recombinant viruses were more sensitive to neutralization by a panel of HIV-positive sera than was VH-rBORI. Interestingly, the CD4-induced 17b epitope on gp120 was more accessible in the rB15 and rV1V2 pseudotypes than in rBORI, even before CD4 binding, and concomitantly, the rB15 and rV1V2 pseudotypes were more sensitive to neutralization with the human 17b monoclonal antibody. Adaptation to growth in microglia--cells that have reduced expression of CD4 in comparison with other cell types--appears to be associated with changes in gp120 that modify its ability to utilize CD4 and CCR5. Changes in the availability of the 17b epitope indicate that these affect conformation. These results imply that the process of adaptation to certain tissue types such as the CNS directly affects the interaction of HIV-1 envelope glycoproteins with cell surface components and with humoral immune responses.
Insights
Human immunodeficiency virus type 1 (HIV-1) adapted to grow in microglia shows altered envelope glycoproteins. These changes enhance its ability to infect cells with low CD4 and CCR5 levels, impacting immune responses.
Area of Science:
- Virology
- Immunology
- Neuroscience
Background:
- Human immunodeficiency virus type 1 (HIV-1) infects central nervous system (CNS) microglial cells, inducing syncytium formation.
- Sequential passaging of HIV-1(BORI) in microglia yielded HIV-1(BORI-15), exhibiting enhanced fusion and replication in these cells.
- The parent and adapted viruses utilized CCR5 as a coreceptor, with syncytium-inducing phenotype linked to four amino acid changes in the V1/V2 region of gp120.
Purpose of the Study:
- To investigate the impact of microglial adaptation on HIV-1 envelope glycoproteins (gp120) and their interaction with cell surface receptors (CD4 and CCR5).
- To characterize the infectivity and neutralization sensitivity of recombinant HIV-1 viruses with specific gp120 modifications.
- To understand how adaptation to CNS microglial cells influences HIV-1's interaction with host cell receptors and immune responses.
Main Methods:
- Production of luciferase-reporter, env-pseudotyped viruses (rBORI, rB15, rV1V2) using plasmids encoding specific HIV-1 env sequences.
- Infection of cells expressing varying levels of CD4 and CCR5 with pseudotyped viruses.
- Assessment of infectivity with chimeric or deleted coreceptors and neutralization sensitivity using HIV-positive sera and the 17b monoclonal antibody.
Main Results:
- Adapted viruses (rB15, rV1V2) maintained infectivity in cells with low CD4 levels, independent of CCR5 levels, and utilized modified coreceptors.
- The CD4-induced 17b epitope on gp120 was more accessible in adapted viruses, increasing sensitivity to 17b antibody neutralization.
- Adapted viruses showed increased sensitivity to neutralization by a panel of HIV-positive sera compared to the parent virus.
Conclusions:
- Adaptation of HIV-1 to microglia involves gp120 changes that enhance utilization of CD4 and CCR5, particularly under low receptor expression conditions.
- Conformational changes in gp120, evidenced by altered 17b epitope accessibility, are associated with microglial adaptation.
- HIV-1 adaptation to specific tissue types like the CNS directly modulates envelope glycoprotein interactions with cell surface molecules and humoral immune responses.
