Dino B.A. Tan

TLR2-induced cytokine responses may characterize HIV-infected patients experiencing mycobacterial immune restoration disease.

Objectives:Most HIV patients who experience Mycobacterium tuberculosis-associated immune restoration disease (TB IRD) display elevated interferon-gamma (IFN&ggr;) responses against mycobacterial antigens, but these can occur without an IRD. Recognition of mycobacteria-associated molecular patterns through toll-like receptors (TLRs) on dendritic cells and monocytes induces cytokine production. Here, we investigate TLR-induced responses in IRD. Design:Peripheral blood mononuclear cells (PBMCs) were collected at approximately weeks 0, 6, 12, 24 and 48 after antiretroviral therapy from five patients experiencing TB IRD, nine matched non-IRD patients and 15 healthy controls. Methods:IFN&ggr; production by PBMC stimulated with protein purified derivative (PPD) was assessed by ELISpot. TLR2 expression on myeloid dendritic cells (mDCs) and monocytes was assessed by flow cytometry. TNF&agr;, IL-12p40 and IL-10 were measured by ELISA in 24-h cultures of PBMC with lipomannan (mycobacteria-derived TLR2 agonist). Results:TLR2 expression on mDC and monocytes was higher in patients than controls at baseline (P < 0.005). TLR2 expression decreased to normal levels on mDC by week 12, but remained higher on monocytes at week 24 (P = 0.02). At week 24, IRD patients showed higher IFN&ggr; responses to PPD (P = 0.02), TLR2 expression on monocytes (P = 0.006) and lipomannan-induced TNF&agr; production (P = 0.016) than non-IRD patients. Lipomannan-induced TNF&agr; and IL-12p40 responses paralleled TB IRD in the patients with high TLR2 expression. IL-10 levels did not associate with IRD. Conclusion:TLR2-induced pro-inflammatory cytokines by dendritic cells or monocytes may contribute to the pathogenesis of mycobacterial IRD.

Impaired function of regulatory T-cells in patients with chronic obstructive pulmonary disease (COPD)

Anti-inflammatory pathways affecting chronic obstructive pulmonary disease (COPD) are poorly understood. Regulatory T-cells (Tregs) are important negative regulators of T-cell activity and hence were investigated in COPD patients in this study. We hypothesised that functional defects in Tregs may promote increased inflammation contributing to the pathogenesis of COPD. Peripheral blood mononuclear cells (PBMC) were isolated from patients with stable COPD and age-matched non-smoking controls. Treg-mediated suppression of memory non-Treg (Foxp3(-)CD45RO(+)) CD4(+) T-cell activation was analysed by comparing PBMC responses to staphylococcal enterotoxin-B (SEB) pre- and post-depletion of Tregs (CD25(+)CD127(low)CD4(+) T-cells) by fluorescence-activated cell sorting (FACS). Activation of T-cells was assessed by HLA-DR expression. Levels of secreted cytokines were measured by ELISA. Depletion of Tregs increased SEB-induced activation of Foxp3(-)CD45RO(+) CD4(+) T-cells in samples from 15/15 healthy controls (demonstrating Treg-mediated suppression) and 9/14 COPD patients (Fishers test, p=0.017). A screen of clinical data associated a failure of Treg-mediated suppression in the remaining five COPD patients with a higher body mass index (BMI) (33-38 kg/m(2)) compared to patients with unimpaired Treg function (20-32 kg/m(2)). In conclusion, we demonstrate impaired Treg-mediated suppression of CD4(+) T-cell activation in a subset of COPD patients, all of whom had high BMI. Obesity and/or perturbed homeostasis of Treg subsets may explain this defect and therefore contribute to increased inflammation observed in COPD.

Viremic HIV Controllers Exhibit High Plasmacytoid Dendritic Cell–Reactive Opsonophagocytic IgG Antibody Responses against HIV-1 p24 Associated with Greater Antibody Isotype Diversification

Identifying the mechanisms of natural control of HIV-1 infection could lead to novel approaches to prevent or cure HIV infection. Several studies have associated natural control of HIV-1 infection with IgG Abs against HIV-1 Gag proteins (e.g., p24) and/or production of IgG2 Abs against HIV-1 proteins. These Abs likely exert their effect by activating antiviral effector cell responses rather than virus neutralization. We hypothesized that an opsonophagocytic IgG Ab response against HIV-1 p24 that activates plasmacytoid dendritic cells (pDCs) through FcγRIIa would be associated with control of HIV and that this would be enhanced by Ab isotype diversification. Using the Gen2.2 pDC cell line, we demonstrated that pDC-reactive opsonophagocytic IgG Ab responses against HIV-1 p24 were higher in HIV controllers (HIV RNA < 2000 copies/ml) than noncontrollers (HIV RNA > 10,000 copies/ml), particularly in controllers with low but detectable viremia (HIV RNA 75–2000 copies/ml). Opsonophagocytic Ab responses correlated with plasma levels of IgG1 and IgG2 anti-HIV-1 p24 and, notably, correlated inversely with plasma HIV RNA levels in viremic HIV patients. Phagocytosis of these Abs was mediated via FcγRIIa. Isotype diversification (toward IgG2) was greatest in HIV controllers, and depletion of IgG2 from Ig preparations indicated that IgG2 Abs to HIV-1 p24 do not enhance phagocytosis, suggesting that they enhance other aspects of Ab function, such as Ag opsonization. Our findings emulate those for pDC-reactive opsonophagocytic Ab responses against coxsackie, picorna, and influenza viruses and demonstrate a previously undefined immune correlate of HIV-1 control that may be relevant to HIV vaccine development.

Levels of anti-cytokine antibodies may be elevated in patients with pulmonary disease associated with non-tuberculous mycobacteria

Pulmonary disease due to non-tuberculous mycobacteria (NTM) is caused by several species (particularly Mycobacterium avium, Mycobacterium intracellulare) that are abundant in the environment. Th1 cytokines such as interferon (IFN)-γ are important in the control of mycobacteria, but in vitro production of IFN-γ is not deficient in adult patients with pulmonary NTM disease. Antibodies reactive with IFN-γ have been described in patients with disseminated NTM disease, but it is not clear whether they are common in pulmonary disease. Here we show that patients with pulmonary NTM have a higher level of anti-IFN-γ and anti-GM-CSF antibodies than healthy controls, although some controls also have high levels. Levels of anti-IFN-γ antibodies did not correlate with levels of total immunoglobulin. Longitudinal studies are required to determine whether anti-cytokine autoantibodies are consequence rather than a cause of pulmonary NTM disease.

Levels of CMV-reactive antibodies correlate with the induction of CD28(null) T cells and systemic inflammation in chronic obstructive pulmonary disease (COPD).

Chronic obstructive pulmonary disease (COPD) is characterized by chronic irreversible inflammation and progressive decline in lung function. While smoking and other environmental agents (e.g., air pollutants) are common causes of COPD, the major challenges in managing this condition are the persistent inflammation and functional deterioration which are not reversed by removal of precipitating agents (e.g., smoking cessation) or treatment with anti-inflammatory agents. We hypothesized that the reactivation of latent CMV infection may trigger expansion of pro-inflammatory CD28null T cells and hence promote sysmetic inflammation in patients with COPD. This study presents novel data showing increased levels of CMV-reactive IgM and IgG in COPD patients compared to controls. This paralleled observed increases in markers of sytemic inflammation ex vivo and proportions of circulating CD28null T cells. This mechanism may explain the persistent inflammation in COPD patients.

Control of early HIV-1 infection associates with plasmacytoid dendritic cell-reactive opsonophagocytic IgG antibodies to HIV-1 p24

Objectives:We have previously demonstrated that HIV-1 p24-specific plasmacytoid dendritic cell-reactive opsonophagocytic antibody (PROAb) responses associate with control of chronic HIV infection. Here, we examined whether HIV-1 p24-specific PROAbs associate with control of early HIV infection and their relationship with HIV-1 p24-specific IgG subclasses. Methods:Plasma collected at 8 and 52 weeks following primary HIV-1 infection was obtained from antiretroviral therapy-naïve patients who were classified as ‘good’ (plasma HIV-1 RNA < 5000 copies/ml; n = 17) or ‘poor’ (HIV-1 RNA > 50 000 copies/ml; n = 15) controllers at week 52. HIV-1 p24-specific PROAb responses were assayed using a plasmacytoid dendritic cell line (Gen2.2), and HIV-1 p24-specific IgG3, IgG1 and IgG2 levels were assayed by ELISA. Results:HIV-1 p24-specific PROAb responses increased in ‘good controllers’ (P = 0.01) but remained unchanged in ‘poor controllers’ between weeks 8 and 52. Of the HIV-1 p24-specific IgG subclasses measured, only IgG1 increased over this time period in ‘good controllers’ alone (P = 0.003), which correlated with the increase in HIV-1 p24-specific PROAb responses (r = 0.83, P < 0.0001). Depletion of IgG1 from IgG preparations of ‘good controllers’ resulted in the inhibition of HIV-1 p24-specific PROAb responses. In the total patient cohort, plasma HIV-1 RNA levels at week 52 correlated inversely with changes in HIV-1 p24-specific PROAb responses (r = −0.37, P = 0.04) and IgG1 (r = −0.51, P = 0.003) levels between weeks 8 and 52. Conclusion:Control of early HIV-1 infection was associated with an increase in HIV-1 p24-specific PROAb responses, which was mediated by HIV-1 p24-specific IgG1 antibodies. These findings provide further evidence that antibodies to HIV core proteins may contribute to control of HIV-1 infection.

Human mesenchymal stem cells attenuate early damage in a ventilated pig model of acute lung injury

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a major cause of global morbidity and mortality. Mesenchymal stem cells (MSC) have shown promise in treating inflammatory lung conditions. We hypothesised that human MSC (hMSC) can improve ALI/ARDS through their anti-inflammatory actions. We subjected pigs (n=6) to intravenous oleic acid (OA) injury, ventilation and hMSC infusion, while the controls (n=5) had intravenous OA, ventilation and an infusion vehicle control. hMSC were infused 1h after the administration of OA. The animals were monitored for additional 4h. Nuclear translocation of nuclear factor-light chain enhancer of activated B cells (NF-κB), a transcription factor that mediates several inflammatory pathways was reduced in hMSC treated pigs compared to controls (p=0.04). There was no significant difference in lung injury, assessed by histological scoring in hMSC treated pigs versus controls (p=0.063). There was no difference in neutrophil counts between hMSC-treated pigs and controls. Within 4h, there was no difference in the levels of IL-10 and IL-8 pre- and post-treatment with hMSC. In addition, there was no difference in hemodynamics, lung mechanics or arterial blood gases between hMSC treated animals and controls. Subsequent studies are required to determine if the observed decrease in inflammatory transcription factors will translate into improvement in inflammation and in physiological parameters over the long term.

An evaluation of CD39 as a novel immunoregulatory mechanism invoked by COPD

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are characterized by increased pulmonary and systemic inflammation and commonly caused by bacterial and/or viral infection. Little is known about the T-cell dysregulation in AECOPD that promotes these outcomes. CD39 is an ectonucleotidase able to hydrolyse adenosine triphosphate to create adenosine that may inhibit T-cell responses in patients with AECOPD. Here T-cell expression of CD39 measured by flow cytometry was higher in AECOPD patients than stable COPD patients or healthy controls. Higher expression of CD39 was associated with higher levels of plasma soluble tumor necrosis factor receptor but lower interferon-γ (IFNγ) levels in supernatants from staphylococcal enterotoxin-B stimulated peripheral blood mononuclear cells. This links increased expression of CD39 with systemic inflammation and impaired T-cell responses (e.g. IFNγ). The blockade of CD39 pathways may be a novel approach to the control of AECOPD, reducing the dependency on antibiotics.

Increased CTLA-4+ T cells may contribute to impaired T helper type 1 immune responses in patients with chronic obstructive pulmonary disease

Impaired T helper type 1 (Th1) function is implicated in the susceptibility of patients with chronic obstructive pulmonary disease (COPD) to respiratory infections, which are common causes of acute exacerbations of COPD (AECOPD). To understand the underlying mechanisms, we assessed regulatory T (Treg) cells and the expression of an inhibitory T‐cell receptor, cytotoxic T‐lymphocyte‐associated antigen 4 (CTLA‐4). Cryopreserved peripheral blood mononuclear cells (PBMC) from patients with AECOPD (n = 17), patients with stable COPD (sCOPD; n = 24) and age‐matched healthy non‐smoking controls (n = 26) were cultured for 24 hr with brefeldin‐A or monensin to detect intracellular or surface CTLA‐4 (respectively) by flow cytometry. T cells in PBMC from AECOPD (n = 9), sCOPD (n = 14) and controls (n = 12) were stimulated with anti‐CD3 with and without anti‐CTLA‐4 blocking antibodies and cytokines were quantified by ELISA. Frequencies of circulating T cells expressing intracellular CTLA‐4 were higher in sCOPD (P = 0·01), whereas patients with AECOPD had more T cells expressing surface CTLA‐4 than healthy controls (P = 0·03). Increased frequencies of surface CTLA‐4+ CD4+ T cells and CTLA‐4+ Treg cells paralleled increases in plasma soluble tumour necrosis factor receptor‐1 levels (r = 0·32, P = 0·01 and r = 0·29, P = 0·02, respectively) in all subjects. Interferon‐γ responses to anti‐CD3 stimulation were inversely proportional to frequencies of CD4+ T cells expressing intracellular CTLA‐4 (r = −0·43, P = 0·01). Moreover, CTLA‐4 blockade increased the induction of interferon‐γ, tumour necrosis factor‐α and interleukin‐6 in PBMC stimulated with anti‐CD3. Overall, chronic inflammation may expand sub‐populations of T cells expressing CTLA‐4 in COPD patients and therefore impair T‐cell function. CTLA‐4 blockade may restore Th1 function in patients with COPD and so aid the clearance of bacterial pathogens responsible for AECOPD.

The association of HIV-1 Gag-specific IgG antibodies with natural control of HIV-1 infection in individuals not carrying HLA-B*57: 01 is only observed in viremic controllers.

To expand upon our previous observation that HIV-1 Gag-specific IgG antibodies were highest in HIV controllers not carrying HLA-B*57:01, we analysed these antibodies in a larger cohort of viremic controllers (VCs) or elite controllers (ECs) considering carriage of ‘protective’ HLA-B alleles. HIV-1 p24-specific IgG1 and IgG2 antibodies were higher only in HLA-B*57:01− VCs but there were no differences in ECs. Associations of HIV-1 gp140-specific IgG antibodies with HLA-B*57:01 carriage were inconsistent amongst VCs and ECs.