Cytokines from lymphoid organs of HIV-infected patients: production and role in the immune disequilibrium of the disease

HIV-1 Tat protein induces the production of IDO in human monocyte derived-dendritic cells through a direct mechanism: effect on T cells proliferation

During HIV-1 infection, an increase of indoleamine 2,3 dioxygenase (IDO) expression, and dendritic cells (DC) dysfunction were often associated with AIDS disease progression. In this work, we investigated the effect of HIV-1 Tat protein on the expression of IDO, in MoDCs. We show that Tat induces IDO protein expression and activity in a dose dependent manner by acting at the cell membrane. Using Tat-mutants, we show that the N-Terminal domain, Tat 1–45, but not the central region, Tat 30–72, is sufficient to induce the expression of active IDO. Tat protein is also able to induce several cytokines in MoDCs, including IFN-γ, a strong inducer of IDO. In order to understand whether IDO is induced directly by Tat protein or indirectly following IFN-γ production, complementary experiments were performed and showed that: i) at the kinetic level, Tat induced IDO expression before the production of IFN-γ ii) treatment of MoDCs with Tat-conditioned medium was unable to stimulate IDO expression, iii) coculture of MoDCs in a transwell cell system did not allow IDO expression in MoDCs not previously treated by Tat, iv) direct contact between Tat-treated and untreated MoDCs was not sufficient to induce IDO expression in a Tat-independent manner, and v) treatment of MoDCs in the presence of IFN-γ pathway inhibitors, Jak I and Ly294002, inhibited IFN-γ-induced IDO but had no effect on Tat-induced IDO. At the functional level, our data showed that treatment of MoDCs with Tat led to the inhibition of their capacity to stimulate T cell proliferation. This impairement was totally abolished when the stimulation was performed in the presence of 1MT, an inhibitor of IDO activity, arguing for the implication of the kynurenine pathway. By inducing IDO, Tat protein may be considered, as a viral pathogenic factor, in the dysregulation of the DC functions during HIV-1 infection.

Human immunodeficiency virus type 1 Tat protein induces an intracellular calcium increase in human monocytes that requires DHP receptors: involvement in TNF-alpha production

HIV-1 Tat protein, acting at the cell membrane, stimulates the production by human monocytes of TNF-alpha, a cytokine implicated in both HIV-1 replication and pathogenesis. Here, we analyze, in primary human monocytes, the mechanisms involved in Tat-stimulated calcium mobilization and its relationship with TNF-alpha production. We show that the Tat protein induces a calcium signal by mobilizing calcium from extracellular stores. This calcium signal is totally blocked when cells are stimulated in the presence of DHP receptor inhibitors such as nimodipine or calcicludine, thus suggesting the implication of this L-type calcium channel. By using RT-PCR amplification, Western blot with antibodies directed against the alpha1D subunit, binding assays with specific agonists or antagonists, and inhibition with specific antisense oligonucleotides, we show that DHP receptors are expressed and functional in primary human monocytes. Interestingly, we demonstrate that Tat-induced calcium mobilization is tightly linked to TNF-alpha production, thus indicating that Tat-induced mobilization and TNF-alpha production are entirely mediated by DHP receptors, as shown by their total inhibition by nimodipine, calcicludine, or anti-alpha1D antisense oligonucleotides.

The AIDS disease of CD4C/HIV transgenic mice shows impaired germinal centers and autoantibodies and develops in the absence of IFN-gamma and IL-6

The mechanisms responsible for degeneration of germinal centers (GC) and follicular dendritic cell (FDC) networks during progression to AIDS remain elusive. Here, we show that CD4(+) T cells from CD4C/HIV-1 Tg mice, which develop a severe AIDS-like disease, express low levels of CD40 ligand. Accordingly, GC formation, FDC networks, and immunoglobulin isotype switching are impaired in these animals. However, Tg B cells respond to in vitro CD40 stimulation. Total serum IgG levels are reduced in Tg mice, whereas total IgM levels are increased with a significant amount showing DNA specificity. IFN-gamma- and IL-6-deficient CD4C/HIV Tg mice also develop the AIDS-like disease and produce auto-Ab. Thus, CD4C/HIV Tg mice have immune dysfunction accompanied by autoimmune responses.

Gastrointestinal T lymphocytes retain high potential for cytokine responses but have severe CD4(+) T-cell depletion at all stages of simian immunodeficiency virus infection compared to peripheral lymphocytes

Gastrointestinal complications in human immunodeficiency virus (HIV) infection are indicative of impaired intestinal mucosal immune system. We used simian immunodeficiency virus (SIV)-infected rhesus macaques as an animal model for HIV to determine pathogenic effects of SIV on intestinal T lymphocytes. Intestinal CD4(+) T-cell depletion and the potential for cytokine responses were examined during SIV infection and compared with results for lymphocytes from lymph nodes and blood. Flow cytometric analysis demonstrated severe depletion of CD4(+)CD8(-) single-positive T cells and CD4(+)CD8(+) double-positive T cells in intestinal lamina propria lymphocytes (LPL) and intraepithelial lymphocytes (IEL) during primary SIV infection which persisted through the entire course of SIV infection. In contrast, CD4(+) T-cell depletion was gradual in peripheral lymph nodes and blood. Flow cytometric analysis of intracellular gamma interferon (IFN-gamma) and interleukin-4 (IL-4) production following short-term mitogenic activation revealed that LPL retained same or higher capacity for IFN-gamma production in all stages of SIV infection compared to uninfected controls, whereas peripheral blood mononuclear cells displayed a gradual decline. The CD8(+) T cells were the major producers of IFN-gamma. There was no detectable change in the frequency of IL-4-producing cells in both LPL and peripheral blood mononuclear cells. Thus, severe depletion of CD4(+) LPL and IEL in primary SIV infection accompanied by altered cytokine responses may reflect altered T-cell homeostasis in intestinal mucosa. This could be a mechanism of SIV-associated enteropathy and viral pathogenesis. Dynamic changes in intestinal T lymphocytes were not adequately represented in peripheral lymph nodes or blood.

Cytokines and chemokines in HIV infection: implications for therapy

HIV infection is associated with both a hyperactivity of the immune system and decreased immune responses against specific antigens. A similar pattern is observed when considering cytokine production in HIV-infected patients. Several cytokines are spontaneously produced at an increased level, whereas other cytokines playing an important role during cell-mediated immune responses are produced at a low level following stimulation. This deregulation of cytokine production may participate to the immune deficiency, both by impairing immune responses and by accelerating CD4+ T lymphocyte destruction. Chemokine receptors have recently been shown to function as coreceptors for the virus, and to govern its cellular tropism. Heterogeneous expression of chemokine receptor may contribute to differences in infectability as well as in rate of progression of the disease between individuals. Better understanding of the role of cytokines and chemokines in HIV infection suggests new therapeutic approaches where administration of cytokines or cytokine antagonists may allow the immune system to function in better conditions, to stimulate antiviral and antiinfectious immune defenses, and to limit viral spread.

HIV infection alters the production of both type 1 and 2 cytokines but does not induce a polarized type 1 or 2 state

OBJECTIVE

To test the T-helper (TH)1/TH2 cytokine paradigm in HIV infection.

DESIGN AND METHODS

Cytokine profiles in two separate studies of HIV patients and controls are presented: (i) a longitudinal study of HIV patients with CD4 counts > 500 x 10(6)/l tested at three timepoints compared with controls; (ii) a blinded cross-sectional study of controls and patients with high (> 500 x 10(6)/l) and low (< 500 x 10(6)/l) CD4 counts. Peripheral blood mononuclear cells (PBMC) from patients and controls were tested for the production of two type 1 [interleukin (IL)-2, interferon (IFN)-gamma] and two type 2 (IL-4, IL-10) cytokines by enzyme-linked immunosorbent assay. Both spontaneous and mitogen-induced cytokine production was measured.

RESULTS

HIV infection was noted to have the following effects on cytokine production: (i) it led to the in vivo activation of type 2 cytokines in a small group of individuals with high CD4 numbers characterized by the spontaneous release of IL-4 and IL-10. Longitudinal data showed high spontaneous IL-4 and IL-10 to be a consistent feature of the patient group (at each timepoint some patients were high producers) but to be variable in a given individual; (ii) HIV infection impaired the ability of PBMC to respond to stimuli (selected for their ability to optimally induce each cytokine) in terms of IL-2, IL-4 and IL-10 production in patients with both high and low CD4 cell counts; and (iii) conversely, HIV infection led to an overproduction of IFN-gamma in patients with high CD4 counts; patients with low CD4 produced normal levels of IFN-gamma.

CONCLUSIONS

Our observations did not suggest polarization of the type 1/type 2 cytokine profile in HIV patients. Instead, the data suggested more complex changes to type 1/type 2 cytokine patterns in HIV infection than originally proposed by the TH1/TH2 dichotomy.

Massive production of Th2 cytokines by human CD4+ effector T cells transiently expressing the natural killer cell marker CD57/HNK1

We have reported previously that uncommitted human CD4+ CD45RO- T cells default to the T-helper type 1 (Th1) pathway, if they are costimulated by anti-CD3 plus anti-CD28 monoclonal antibodies (mAb). In contrast, 5% of the uncommitted T cells differentiate into Th2 cells, if they are stimulated by anti-CD28 plus interleukin-2 (IL-2) in the absence of T-cell receptor (TCR) signals. The anti-CD28/IL-2-induced proliferation (and the resulting Th2 commitment) was not affected by neutralizing anti-IL-4 mAb, suggesting a non-conventional IL-4-independent Th2 differentiation pathway. Here we report that the respective CD4+ Th2 cells (but not the Th1 cells) coexpressed the natural killer (NK) cell marker HNK1/CD57. Expression of CD57 on Th2 cells required CD28 stimulation, and was suppressed by CD3/TCR signals. However, Th2 effector cells displayed a TCR V beta-chain usage comparable to that of committed Th1 cells (with V beta 8 dominating). Our data suggest that expression of CD57 on human CD4 T cells may be associated with defined stages of Th2 cell activation/differentiation, and may not necessarily characterize a separate T-cell lineage. The induction of cytokine production and B-cell helper function in both Th1 and Th2 populations required CD3/TCR signalling in costimulation with anti-CD28 or IL-2. Importantly, anti-CD28/IL-2-primed Th2 cells readily secreted IL-4 and induced IgE production by surface IgE- B cells in response to the first TCR signal and independent of previous contact with IL-4. Therefore, CD4+ CD57+ T cells responded comparably to murine CD4+ NK1.1+ T cells, which are critical for the development of Th2/IgE immune responses in vivo. The possible role of human CD4+ CD57/HNK1+ Th2-like cells in cancer, infection and allergy is discussed.

Differential production of interleukin 10 during human immunodeficiency virus infection

Interleukin 10, a product of T and B cells and monocytes, displays many Th2-like properties through inhibition of Th1 cell functions. Interleukin 10 is thought to play a major role in the immune dysfunction seen in HIV-infected individuals. In this study, we evaluated in detail the production of IL-10 during HIV infection. Although the constitutive production of IL-10 did not differ in PBMCs from healthy donors and HIV-infected individuals, IL-10 was differentially produced in response to polyclonal activators. The overall plasma IL-10 levels were similar in 32 controls and 67 patients at different stages of the disease and receiving different antiretroviral drugs. However, patients with low CD4 T cell count (< 200/mm3) secreted approximately three-fold more IL-10 than did patients with high CD4 T cell count (> 500/mm3). Competitive/quantitative PCR revealed similar levels of mRNA expression in PBMCs from controls and HIV-infected individuals. In vitro HIV infection rapidly and transiently induced IL-10 production in PBMCs and monocytes, and the low level of endogenously secreted IL-10 failed to inhibit HIV replication in acutely infected monocytes. On the other hand, HIV infection of selected CD4+ T cell clones generated in a Th1- or Th2-like environment, differentially up-regulated IL-10 production, with significantly higher production by Th2 clones. Together, our data indicate that IL-10 production is more complex than previously thought, and may depend on several factors such as producer cells, nature of the stimuli, as well as viral isolates.