CXCR4-mediated T cell apoptosis in human immunodeficiency virus infection

HIV-1 Nef interacts with HCV Core, recruits TRAF2, TRAF5 and TRAF6, and stimulates HIV-1 replication in macrophages

Tumor necrosis factor receptor-associated factor (TRAF) signaling plays a central role in many biological activities, such as the regulation of immune and inflammatory responses and control of apoptosis, which are key events in the pathogenesis of the human immunodeficiency virus (HIV)-1 and the hepatitis C virus (HCV) infections. Here we show that TRAF2, TRAF5 and TRAF6 interact with the HIV-1 Nef protein, an immunomodulatory viral protein expressed and released by cells infected by the virus. We also found that TRAF2 and TRAF5 interact with the HCV Core protein. Interestingly, we observed that HIV-1 Nef interacts with HCV Core. The activation of TRAF (2, 5, 6) - mediated by HIV-1 Nef and HCV Core - enhanced the activation of the nuclear factor-kappa B (NF-κB) and increased HIV-1 replication in monocyte- derived macrophages (MDMs). The knockdown of TRAF2, TRAF5 and TRAF6 resulted in decreased NF-κB activation and reduced HIV-1 replication in MDMs. Our results reveal a mechanism by which the activation of the TRAF pathway by HIV-1 Nef and HCV Core favors the replication of HIV-1 in macrophages and could be a critical factor for optimal replication of HIV-1 in macrophages of HIV-HCV-coinfected patients.

Macrophage signaling in HIV-1 infection

The human immunodeficiency virus-1 (HIV-1) is a member of the lentivirus genus. The virus does not rely exclusively on the host cell machinery, but also on viral proteins that act as molecular switches during the viral life cycle which play significant functions in viral pathogenesis, notably by modulating cell signaling. The role of HIV-1 proteins (Nef, Tat, Vpr, and gp120) in modulating macrophage signaling has been recently unveiled. Accessory, regulatory, and structural HIV-1 proteins interact with signaling pathways in infected macrophages. In addition, exogenous Nef, Tat, Vpr, and gp120 proteins have been detected in the serum of HIV-1 infected patients. Possibly, these proteins are released by infected/apoptotic cells. Exogenous accessory regulatory HIV-1 proteins are able to enter macrophages and modulate cellular machineries including those that affect viral transcription. Furthermore HIV-1 proteins, e.g., gp120, may exert their effects by interacting with cell surface membrane receptors, especially chemokine co-receptors. By activating the signaling pathways such as NF-kappaB, MAP kinase (MAPK) and JAK/STAT, HIV-1 proteins promote viral replication by stimulating transcription from the long terminal repeat (LTR) in infected macrophages; they are also involved in macrophage-mediated bystander T cell apoptosis. The role of HIV-1 proteins in the modulation of macrophage signaling will be discussed in regard to the formation of viral reservoirs and macrophage-mediated T cell apoptosis during HIV-1 infection.

Emergence and persistence of CXCR4-tropic HIV-1 in a population of men from the multicenter AIDS cohort study

We examined the emergence of CXCR4 (i.e., X4) tropism in 67 male human immunodeficiency virus type 1 (HIV-1) seroconverters from the Multicenter AIDS Cohort Study (MACS) who were selected to reflect the full spectrum of rates of HIV-1 disease progression. A mean of 10 serial samples per donor were evaluated by a laboratory-validated, commercially available assay to determine phenotypic coreceptor use. A total of 52% of men had dual- or mixed-tropic HIV-1 detected at 1 or more of the time points tested. Use of X4 by HIV-1 was detected more frequently among men who developed AIDS (defined as a CD4(+) T cell count of <200 cells/muL and/or an AIDS-defining illness) < or =11 years after seroconversion than among those who did not (P = .005), as well as among men who exhibited a total T cell count decline (i.e., a CD3(+) inflection point), compared with those who did not (P = .03). For men in whom both X4 virus and an inflection point were detected, emergence of X4 virus preceded the inflection point by a median of 0.83 years. The median CD4(+) T cell count at first detection of X4 viruses before the onset of AIDS was 475 cells/microL. We conclude that HIV-1 variants that used X4 frequently emerged at high CD4(+) T cell counts and may contribute to the decrease in T cell numbers during late HIV-1 infection.

CD8 apoptosis may be a predictor of T cell number normalization after immune reconstitution in HIV

Background

As part of the Houston Vanguard study, a subset of 10 patients randomized to receive IL-2 therapy were compared to 4 patients randomized to not receive IL-2, for markers of T cell activation and death during the first three cycles of IL-2. All patients were treated with combination antiretroviral therapy (ART) and were virally suppressed. The purpose of the study was to examine the role of CD8+ T cell death in responses to ART and IL-2 therapy.

Methods

Lymphocytes were examined at Day 0, 5 and 30 days during three cycles of IL-2 therapy. CD25, CD38, HLA-DR expression and annexin (cell death) were examined on CD4 and CD8 subpopulations. Follow up studies examined CD4 levels and CD4:CD8 reconstitution after 6 years using both univariant and multivariate analyses.

Results

Human lymphocytes responded to IL-2 therapy by upregulation of CD25 on CD4⁺ T cells, leading to an increase in CD4 cell counts. CD8⁺ T cells did not increase CD25 expression, but upregulated activation antigens (CD38 and DR) and had increased death. At baseline, 7 of the 14 patients had high CD8⁺ T cell apoptosis (mean 17.0% ± 6.0). We did an exploratory analysis of immune status after six years, and found that baseline CD8⁺ T cell apoptosis was correlated with CD4 cell count gain beginning two years post enrollment. Patients with low levels of CD8⁺ T cell apoptosis at baseline (mean 2.2% ± 2.1) had significantly higher CD4 cell counts and more normalized CD4:CD8 ratios than patients with high CD8⁺ T cell apoptosis (mean CD4 cell counts 1,209 ± 164 vs 754 ± 320 cells/mm³; CD4:CD8 ratios 1.55 vs. 0.70, respectively).

Conclusion

We postulate that CD8⁺ T cell apoptosis may reflect inherent activation status, which continues in some patients even though viral replication is suppressed which influences the ability of CD4⁺ T cells to rebound. Levels of CD8⁺ T cell apoptosis may therefore be an independent predictor of immune status, which should be shown in a prospective study.