Ann Atlas

Loss of IL-7Ralpha is associated with CD4 T-cell depletion, high interleukin-7 levels and CD28 down-regulation in HIV infected patients

Objective:Elevated levels of interleukin (IL)-7 are present in the blood of HIV-positive patients and it is known that IL-7 receptor (IL-7R)α expression decreases on T cells during HIV infection. The subset(s) of T cells with low IL-7Rα and the consequence of low IL-7Rα expression for T-cell survival are poorly characterized. Design:The frequency of IL-7Rα-negative T cells in HIV-positive patients was studied in relation to CD4 T-cell counts, IL-7 concentration and survival in culture. We analysed IL-7Rα expression in different T-cell populations and in relation to Bcl-2 expression. Methods:Specimens from 38 HIV-1 patients and 17 controls were examined. IL-7Rα and Bcl-2 expression in different T-cell populations was studied by flow cytometry. The influence of IL-7Rα expression on T-cell survival was studied by culturing T cells in the presence of IL-7. Results:Down-regulation of IL-7Rα on T cells correlated with depletion of CD4 T cells (P < 0.001) and also with increased concentration of serum IL-7 (P < 0.05). The decreased IL-7Rα expression was associated with low Bcl-2 expression and with the reduced survival capacity of T cells in the presence of IL-7 in vitro. Particularly, T cells with memory phenotype showed a decreased IL-7Rα expression in association with CD28 down-regulation. Conclusions:The positive effects of IL-7 on survival and homeostatic proliferation of T cells might be severely impaired in HIV-infected individuals due to IL-7Rα down-regulation. Differentiation towards a CD28-negative memory phenotype in response to chronic activation may lead to an overall decrease of IL-7 mediated survival within the peripheral T-cell pool.

Broadly Immunogenic HLA Class I Supertype-Restricted Elite CTL Epitopes Recognized in a Diverse Population Infected with Different HIV-1 Subtypes

The genetic variations of the HIV-1 virus and its human host constitute major obstacles for obtaining potent HIV-1-specific CTL responses in individuals of diverse ethnic backgrounds infected with different HIV-1 variants. In this study, we developed and used a novel algorithm to select 184 predicted epitopes representing seven different HLA class I supertypes that together constitute a broad coverage of the different HIV-1 strains as well as the human HLA alleles. Of the tested 184 HLA class I-restricted epitopes, 114 were recognized by at least one study subject, and 45 were novel epitopes, not previously described in the HIV-1 immunology database. In addition, we identified 21 “elite” epitopes that induced CTL responses in at least 4 of the 31 patients. A majority (27 of 31) of the study population recognized one or more of these highly immunogenic epitopes. We also found a limited set of 9 epitopes that together induced HIV-1-specific CTL responses in all HIV-1-responsive patients in this study. Our results have important implications for the validation of potent CTL responses and show that the goal for a vaccine candidate in inducing broadly reactive CTL immune responses is attainable.

Altered expression of the receptor-ligand pair CXCR5/CXCL13 in B cells during chronic HIV-1 infection

HIV-1 infection is associated with B-cell abnormalities, such as hypergammaglobulinemia, poor immunization responses, and loss of serologic memory. To determine whether altered expression of chemokine receptors and their ligands may play a role in B-cell dysfunctions during HIV-1 infection, the expression of CXC chemokine receptor 4 (CXCR4), CXCR5, and CC chemokine receptor 7 (CCR7) and their respective ligands on CD19(+) B cells were examined in HIV-1-infected patients and controls. We report a decreased CXCR5 expression on B cells from patients (P < .05), a phenomenon associated with a low CD4 T-cell count (< 350 cells/microL). Interestingly, an increased expression of CXC chemokine ligand 13 (CXCL13), the ligand for CXCR5, was found in peripheral B cells from HIV-1-infected patients. Moreover, on B-cell activation in vitro, CXCL13 was secreted in culture. CXCL13(+) B cells were also found in the lymph nodes of HIV-1-infected patients, but not in control tissue. B-cell migration toward CXCL13, CXCL12, and CC chemokine ligand 21 (CCL21), ligands for CXCR5, CXCR4, and CCR7 was also evaluated. In patients with a low CD4 T-cell count, migration toward all ligands was increased. Our findings indicate that altered expression of the chemokine receptor-ligand pair, CXCR5/CXCL13, may participate in the establishment of B-cell dysfunctions during HIV-1 infection.

Potential Role for IL-7 in Fas-Mediated T Cell Apoptosis During HIV Infection

IL-7 promotes survival of resting T lymphocytes and induces T cell proliferation in lymphopenic conditions. As elevated IL-7 levels occur in HIV-infected individuals in addition to high Fas expression on T cells and increased sensitivity to Fas-induced apoptosis, we analyzed whether IL-7 has a regulatory role in Fas-mediated T cell apoptosis. We show that IL-7 up-regulates Fas expression on naive and memory T cells through a mechanism that involves translocation of Fas molecules from intracellular compartments to the cell membrane. IL-7 induced the association of Fas with the cytoskeletal component ezrin and a polarized Fas expression on the cell surface. The potential role of IL-7 in Fas up-regulation in vivo was verified in IL-7-treated macaques and in HIV-infected or chemotherapy treated patients by the correlation between serum IL-7 levels and Fas expression on T cells. IL-7 treatment primed T cells for Fas-induced apoptosis in vitro and serum IL-7 levels correlated with the sensitivity of T cells to Fas-induced apoptosis in HIV-infected individuals. Our data suggest an important role for IL-7 in Fas-mediated regulation of T cell homeostasis. Elevated IL-7 levels associated with lymphopenic conditions, including HIV-infection, might participate in the increased sensitivity of T cells for activation-induced apoptosis.

CD27− B-Cells Produce Class Switched and Somatically Hyper-Mutated Antibodies during Chronic HIV-1 Infection

Class switch recombination and somatic hypermutation occur in mature B-cells in response to antigen stimulation. These processes are crucial for the generation of functional antibodies. During HIV-1 infection, loss of memory B-cells, together with an altered differentiation of naïve B-cells result in production of low quality antibodies, which may be due to impaired immunoglobulin affinity maturation. In the current study, we evaluated the effect of HIV-1 infection on class switch recombination and somatic hypermutation by studying the expression of activation-induced cytidine deaminase (AID) in peripheral B-cells from a cohort of chronically HIV-1 infected patients as compared to a group of healthy controls. In parallel, we also characterized the phenotype of B-cells and their ability to produce immunoglobulins in vitro. Cells from HIV-1 infected patients showed higher baseline levels of AID expression and increased IgA production measured ex-vivo and upon CD40 and TLR9 stimulation in vitro. Moreover, the percentage of CD27−IgA+ and CD27−IgG+ B-cells in blood was significantly increased in HIV-1 infected patients as compared to controls. Interestingly, our results showed a significantly increased number of somatic hypermutations in the VH genes in CD27− cells from patients. Taken together, these results show that during HIV-1 infection, CD27− B-cells can also produce class switched and somatically hypermutated antibodies. Our data add important information for the understanding of the mechanisms underlying the loss of specific antibody production observed during HIV-1 infection.

Priming of T cells to Fas-mediated proliferative signals by interleukin-7

T-cell depletion associated with HIV infection or cytoreductive therapies triggers potential T-cell regenerative mechanisms such as peripheral T-lymphocyte expansion to weak antigenic stimuli and the increased availability of interleukin-7 (IL-7), a cytokine with potent antiapoptotic and proliferative activities. Deleterious mechanisms also associated with lymphopenia, such as increased Fas expression and apoptosis of T cell, however, may result in opposing effects. In this study, we show that Fas molecules, primarily associated with T-cell depletion in lymphopenic settings, may also contribute to compensatory T-cell expansion through transmitting costimulatory signals to suboptimally activated T cells. Proliferation of T lymphocytes in response to concomitant Fas and T-cell receptor (TCR) triggering was shown to be increased in HIV-infected individuals compared with noninfected controls. As IL-7 levels are often elevated in lymphopenic individuals in association with increased Fas expression, we analyzed whether IL-7 would influence Fas-mediated proliferative signals in T cells. We show that IL-7 is able to increase the efficacy of Fas to induce proliferation of suboptimally activated T cells. Thus, high IL-7 levels associated with lymphopenic conditions may simultaneously induce sensitivity to Fas-mediated apoptosis in nonactivated T cells and increase Fas-induced costimulatory signals in T cells recognizing low-affinity antigens.

Potential role of CD8+CD28-T lymphocytes in immune activation during HIV-1 infection

As CD8+CD28− T cells have been associated with dendritic and T cell suppression, we analyzed whether an increase in CD8+CD28− T cell numbers during HIV-1 infection could lead to impaired T cell responses. In contrast to the in-vitro generated CD8+CD28− suppressors, peripheral blood CD8+CD28− T cells of both HIV-infected and noninfected individuals promoted dendritic cell activation. The CD8+CD28− T cell accumulation during HIV-1 infection may thus contribute to accelerated inflammatory reactions and immune activation.

Sustained Elevation of Kynurenic Acid in the Cerebrospinal Fluid of Patients with Herpes Simplex Virus Type 1 Encephalitis

Herpes simplex virus (HSV) type 1 encephalitis (HSE) is a viral infectious disease with commonly occurring neurodegeneration and neurological/cognitive long-term sequelae. Kynurenic acid (KYNA) is a neuroactive tryptophan metabolite, which is elevated in the cerebrospinal fluid (CSF) during viral infection as a result of immune activation. The aim of the study was to investigate the role of endogenous brain KYNA for the long-term outcome of the disease. CSF KYNA concentration was analyzed in 25 HSE patients along the course of the disease and compared with that of 25 age-matched healthy volunteers. Within 3 weeks of admission CSF KYNA of HSE patients was markedly elevated (median 33.6 nM) compared to healthy volunteers (median 1.45 nM). Following a decline observed after 1–2 months, levels of CSF KYNA were elevated more than 1 year after admission (median 3.4 nM range: 1–9 years). A negative correlation was found between initial CSF KYNA concentrations and severity of the long-term sequelae. This study show a marked elevation in CSF KYNA from patients with HSE, most pronounced during the acute phase of the disease and slowly declining along the recovery. We propose that brain KYNA might potentially protect against neurodegeneration while causing a long-lasting loss in cognitive function associated with the disease.

Loss of IL-7Ra is Associated With CD4+ T Cell Depletion, High IL-7 Levels and CD28 Down-regulation in HIV Infected Patients

We showed that HIV infection is associated with an increased proportion of IL-7Ra low/negative peripheral T lymphocytes. Down-regulation of IL-7Rα on T cells was correlated with the depletion of CD4+ T cells and also with the increased concentration of serum IL-7. The decreased IL-7Rα expression resulted in the reduced survival capacity of T cells in presence of IL-7 and was associated with low Bcl-2 expression. Mostly the memory T cells down-regulated the IL-7Rα and we found a strong association between CD28 and IL-7Rα down-regulation. Accordingly, only CD28+ T cells responded to IL-7 with strong Bcl-2 upregulation.