Chronic activation of the immune system in HIV infection: contribution to T cell apoptosis and V beta selective T cell anergy

Long-term beneficial effect of protease inhibitors on the intrinsic apoptosis of peripheral blood mononuclear cells in HIV-infected patients

BACKGROUND

Viral suppression by antiretroviral therapy (ART) inhibits HIV-induced apoptosis and CD4 T-cell loss. It has been suggested that protease inhibitors (PIs) have nonviral antiapoptotic effects by maintaining mitochondrial integrity. Long-term clinical effects of PI-based ART on mitochondrial toxicity and lymphocyte apoptosis beyond viral suppression have not been exploited to date.

METHODS

We conducted a 7-year study on HIV-1-infected patients from the Cologne HIV cohort with sufficient viral suppression under either a PI-based or nonnucleoside reverse transcriptase inhibitor (NNRTI)-based regimen. Eight patients on PI and eight on NNRTI were eligible for inclusion in the analysis. The primary outcome measure was defined as a change in the mitochondrial-to-nuclear DNA ratio in PBMCs. Further key molecules involved in extrinsic [tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), Fas ligand (FasL) and caspase 8], intrinsic [B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), caspase 9 and lactate-to-pyruvate ratio] and overall apoptosis [Annexin+/7-aminoactinomycin D (7-AAD)- and caspase 3/7] and viral activity [negative regulatory factor (Nef), interferon-α (IFN-α) and myxovirus resistance protein A (MxA)] were measured.

RESULTS

Demographic and baseline clinical parameters were similar in the two groups, except that patients in the PI group had a higher mean age. After 7 years of treatment, CD4 T-cell count increased and the expression of genes encoding the proapoptotic viral protein Nef and HIV-induced cytokine IFN-α and its downstream effector MxA decreased in both groups. Focusing on the different pathways of apoptosis, only in the PI group intrinsic apoptosis decreased significant and in the inter-group comparison the decrease was significantly higher than in the NNRTI group.

CONCLUSIONS

Our study provides evidence that long-term therapy with a PI-based regimen may be superior to that with a NNRTI-based regimen with regard to its intrinsic antiapoptotic effect.

Role of the Fas/FasL pathway in HIV or SIV disease

Human immunodeficiency virus disease involves progressive destruction of host immunity leading to opportunistic infections and increased rates for malignancies. Both depletion in immune cell numbers as well as defects in their effector functions are responsible for this immunodeficiency The broad impact of HIV reflects a similarly broad pattern of cell depletion including subsets that do not express viral receptors or support viral replication. Indirect cell killing, the destruction of uninfected cells, is due partly to activation of the Fas/FasL system for cell death. This death-signaling pathway is induced during HIV disease and contributes significantly to viral pathogenesis and disease.

HIV-induced type I interferon and tryptophan catabolism drive T cell dysfunction despite phenotypic activation

Infection by the human immunodeficiency virus (HIV) is characterized by functional impairment and chronic activation of T lymphocytes, the causes of which are largely unexplained. We cultured peripheral blood mononuclear cells (PBMC) from HIV-uninfected donors in the presence or absence of HIV. HIV exposure increased expression of the activation markers CD69 and CD38 on CD4 and CD8 T cells. IFN-α/β, produced by HIV-activated plasmacytoid dendritic cells (pDC), was necessary and sufficient for CD69 and CD38 upregulation, as the HIV-induced effect was inhibited by blockade of IFN-α/β receptor and mimicked by recombinant IFN-α/β. T cells from HIV-exposed PBMC showed reduced proliferation after T cell receptor stimulation, partially prevented by 1-methyl tryptophan, a competitive inhibitor of the immunesuppressive enzyme indoleamine (2,3)-dioxygenase (IDO), expressed by HIV-activated pDC. HIV-induced IDO inhibited CD4 T cell proliferation by cell cycle arrest in G1/S, and prevented CD8 T cell from entering the cell cycle by downmodulating the costimulatory receptor CD28. Finally, the expression of CHOP, a marker of the stress response activated by IDO, was upregulated by HIV in T cells in vitro and is increased in T cells from HIV-infected patients. Our data provide an in vitro model for HIV-induced T cell dysregulation and support the hypothesis that activation of pDC concomitantly contribute to phenotypic T cell activation and inhibition of T cell proliferative capacity during HIV infection.

Calmodulin antagonists inhibit apoptosis of CD4+ T-cells from patients with AIDS

Recent studies indicate that Fas and Fas ligand are involved in apoptosis of T-cells in HIV-infected patients. We have demonstrated that calcium/calmodulin is involved in Fas-mediated apoptosis in human T-cell lines transfected with HIV recombinant cDNA. In the present study, we examined spontaneous apoptosis of T-cells in vitro in peripheral blood obtained from 11 patients with AIDS and 8 HIV-seronegative normal donors and the effect of the calmodulin antagonists, trifluoperazine (TFP) or tamoxifen (TMX), on apoptosis. The results show that: (1) levels of spontaneous apoptosis were higher in PBMCs obtained from patients with AIDS than HIV-negative normal controls and the levels of apoptosis correlated with the severity of disease. (2) The accelerated apoptosis occurred predominantly in CD4+ cells in patients with AIDS. (3) Calmodulin antagonists inhibited the spontaneous apoptosis of CD4+ T-cells from patients with AIDS, which resulted in an increase in the ratio of CD4+ to CD8+ T-cells. (4) The inhibitory effect of calmodulin antagonists on apoptosis was more significant in patients with advanced disease (CDC category C) compared to less severe disease (CDC category B). These results indicate that calmodulin antagonists inhibit HIV-associated apoptosis of CD4+ T-cells, and imply that the calcium/calmodulin play important roles in mediating apoptosis of CD4+ T-cells induced by HIV infection.