T-cell-mediated and antigen-dependent differentiation of human monocyte into different dendritic cell subsets: a feedback control of Th1/Th2 responses

Dormant Mycobacterium tuberculosis fails to block phagosome maturation and shows unexpected capacity to stimulate specific human T lymphocytes

Dormancy is defined as a stable but reversible nonreplicating state of Mycobacterium tuberculosis. It is currently thought that dormant M. tuberculosis (D-Mtb) is responsible for latent tuberculosis (TB) infection. Recently, D-Mtb was also shown in sputa of patients with active TB, but the capacity of D-Mtb to stimulate specific immune responses was not investigated. We observed that purified protein derivative-specific human CD4(+) T lymphocytes recognize mycobacterial Ags more efficiently when macrophages are infected with D-Mtb instead of replicating M. tuberculosis (R-Mtb). The different Ag recognition occurs even when the two forms of mycobacteria equally infect and stimulate macrophages, which secrete the same cytokine pattern and express MHC class I and II molecules at the same levels. However, D-Mtb but not R-Mtb colocalizes with mature phagolysosome marker LAMP-1 and with vacuolar proton ATPase in macrophages. D-Mtb, unlike R-Mtb, is unable to interfere with phagosome pH and does not inhibit the proteolytic efficiency of macrophages. We show that D-Mtb downmodulates the gene Rv3875 encoding for ESAT-6, which is required by R-Mtb to block phagosome maturation together with Rv3310 gene product SapM, previously shown to be downregulated in D-Mtb. Thus, our results indicate that D-Mtb cannot escape MHC class II Ag-processing pathway because it lacks the expression of genes required to block the phagosome maturation. Data suggest that switching to dormancy not only represents a mechanism of survival in latent TB infection, but also a M. tuberculosis strategy to modulate the immune response in different stages of TB.

Obesity is associated with activated and insulin resistant immune cells

BACKGROUND

Obesity and type 2 diabetes mellitus are characterized by insulin resistance and 'low-grade inflammation'; however, the pathophysiological link is poorly understood. To determine the relative contribution of obesity and insulin resistance to systemic 'inflammation', this study comprehensively characterized circulating immune cells in different grades of obesity.

METHODS

Immune cell phenotypes and activation status were analysed by flow cytometry cross-sectionally in morbidly obese (n = 16, body mass index (BMI) 42.2 ± 5.4 kg/m2), overweight (n = 13, BMI 27.4 ± 1.6 kg/m2) and normal weight (n = 12, BMI 22.5 ± 1.9 kg/m2) subjects.

RESULTS

Obese, but not overweight subjects, had increased activation marker expression on neutrophils, monocytes, T-lymphocytes and polarization of T helper cells towards a pro-inflammatory type 1-phenotype (Th1). Th1 numbers correlated positively with the degree of insulin resistance (homeostasis model assessment, p < 0.05). Lymphocytes from obese subjects showed reduced insulin-stimulated AKT-phosphorylation in vitro. Supra-physiological insulin concentrations did not affect T-cell differentiation, which under normal circumstances would promote an anti-inflammatory T helper type 2-phenotype.

CONCLUSIONS

These results show that morbid obesity is characterized by circulating immune cells that are activated and insulin resistant, with the T-cell balance polarized towards a pro-inflammatory Th1 phenotype. The loss of insulin-induced suppression of inflammatory phenotypes in circulating immune cells could contribute to the systemic and adipose tissue inflammation found in morbid obesity.

Effects of Herbal Medicinal Formulas on Suppressing Viral Replication and Modulating Immune Responses

The Chinese medicinal herbs Radix Isatidis and Viola yedoensis Makino have been suggested to possess antiviral activity. This study tests whether these and other Chinese and Western herbal medicinal formulas can modulate the immune functions involving virus-suppression in BALB/c mouse. We first confirmed the extract from Viola yedoensis Makino, but not from Radix Isatidis, the traditional Chinese medicine (TCM) formula Chui-Uren-Chien (CUC), or a Western homeopathic medicinal drink Método Canova, could inhibit the replications of herpes simplex virus-1 and enterovirus 71 in the human neuroblastoma SK-N-SH cell line. Subsequently, the same herbal extracts and drink underwent toxicity and immunomodulatory tests on mice of 5–7 weeks old. After 8 weeks of feeding different herbal medicinal formulas, no hepatic or renal toxicity was noted in any tested animal; whereas among the immune function evaluations, only the mice treated with CUC extract were found to be associated with significant increases (p < 0.05) in both the level of plasma IgG and the percentage of monocyte in blood mononuclear cells as well as the activation of macrophage Raw264.7 cells for nitric oxide production, suggesting its role in modulating the non-specific immune response. Analyses using protein arrays showed CUC was the most potent herbal medicinal formula eliciting fluctuations in plasma cytokine and chemokine concentrations. Taking all experimental data together, we conclude Chui-Uren-Chien possesses immunomodulatory capability in mouse, but none of the herbal medicinal formulas tested here are involved in strengthening antiviral immunity.

Characterization of monocyte-derived dendritic cells from patients with active and treated paracoccidioidomycosis

Cellular immune responses are a significant defence mechanism in human paracoccidioidomycosis (PCM), an endemic mycosis in Latin America; however, little is known about the role of dendritic cells (DCs) in human PCM. We investigated monocyte-derived DCs from patients with treated (TP) and active PCM (AP) compared with healthy non-PCM donors (CO). DCs from the TP group showed higher expression of HLA-DR, CD86 and DC-SIGN compared with CO, whereas AP showed similar expression to CO. Production of IL-10 was downregulated by TNF-α in all groups and lower levels were observed in untreated DCs from AP compared with CO. Conversely, IL-12p40 was significantly upregulated in the DCs of the TP group. TNF-α-activated DCs from the CO group produced significantly lower levels of IL-12p40 when differentiated from magnetic-sorted monocytes (MACS) compared with adhered monocyte-derived DCs. This comparison in the TP group revealed similar levels of IL-12p40, suggesting a T cell-independent increase in the production of IL-12p40. Higher expression of surface molecules with increased IL-12p40 may indicate a better activation of DCs after the treatment of PCM. Our findings suggest that DCs may be crucial in the protective response to Paracoccidioides brasiliensis and that in vitro-generated DCs might be useful in enhancing antifungal immunity, especially during active PCM.

T(H)1, T(H)2, and T(H)17 cells instruct monocytes to differentiate into specialized dendritic cell subsets

Monocytes and T helper (T(H)) cells rapidly infiltrate inflamed tissues where monocytes differentiate into inflammatory dendritic cells (DCs) through undefined mechanisms. Our studies indicate that T(H) cells frequently interact with monocytes in inflamed skin and elicit the differentiation of specialized DC subsets characteristic of these lesions. In psoriasis lesions, T(H)1 and T(H)17 cells interact with monocytes and instruct these cells to differentiate into T(H)1- and T(H)17-promoting DCs, respectively. Correspondingly, in acute atopic dermatitis, T(H)2 cells interact with monocytes and elicit the formation of T(H)2-promoting DCs. DC formation requires GM-CSF and cell contact, whereas T(H) subset specific cytokines dictate DC function and the expression of DC subset specific surface molecules. Moreover, the phenotypes of T cell-induced DC subsets are maintained after subsequent stimulation with a panel of TLR agonists, suggesting that T(H)-derived signals outweigh downstream TLR signals in their influence on DC function. These findings indicate that T(H) cells govern the formation and function of specialized DC subsets.

T-cell recruitment and Th1 polarization in adipose tissue during diet-induced obesity in C57BL/6 mice

The role of adaptive immunity in obesity-associated adipose tissue (AT) inflammation and insulin resistance (IR) is controversial. We employed flow cytometry and quantitative PCR to assess T-cell recruitment and activation in epididymal AT (eAT) of C57BL/6 mice during 4-22 weeks of a high-fat diet (HFD (60% energy)). By week 6, eAT mass and stromal vascular cell (SVC) number increased threefold in mice fed HFD, coincident with onset of IR. We observed no increase in the proportion of CD3(+) SVCs or in gene expression of CD3, interferon-γ (IFN-γ), or regulated upon activation, normal T-cell expressed and secreted (RANTES) during the first 16 weeks of HFD. In contrast, CD11c(+) macrophages (MΦ) were enriched sixfold by week 8 (P < 0.01). SVC enrichment for T cells (predominantly CD4(+) and CD8(+)) and elevated IFN-γ and RANTES gene expression were detected by 20-22 weeks of HFD (P < 0.01), coincident with the resolution of eAT remodeling. HFD-induced T-cell priming earlier in the obesity time course is suggested by (i) elevated (fivefold) interleukin-12 (IL-12)p40 gene expression in eAT by week 12 (P ≤ 0.01) and (ii) greater IFN-γ secretion from phorbol myristate acetate (PMA)/ionophore-stimulated eAT explants at week 6 (onefold, P = 0.08) and week 12 (fivefold, P < 0.001). In conclusion, T-cell enrichment and IFN-γ gene induction occur subsequent to AT macrophage (ATMΦ) recruitment, onset of IR and resolution of eAT remodeling. However, enhanced priming for IFN-γ production suggests the contribution of CD4(+) and/or CD8(+) effectors to cell-mediated immune responses promoting HFD-induced AT inflammation and IR.

GM-CSF and IL-4 induce dendritic cell differentiation and disrupt osteoclastogenesis through M-CSF receptor shedding by up-regulation of TNF-alpha converting enzyme (TACE)

Monocytes give rise to macrophages, osteoclasts (OCs), and dendritic cells (DCs). Macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB (RANK) ligand induce OC differentiation from monocytes, whereas granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) trigger monocytic differentiation into DCs. However, regulatory mechanisms for the polarization of monocytic differentiation are still unclear. The present study was undertaken to clarify the mechanism of triggering the deflection of OC and DC differentiation from monocytes. GM-CSF and IL-4 abolished monocytic differentiation into OCs while inducing DC differentiation even in the presence of M-CSF and RANK ligand. GM-CSF and IL-4 in combination potently up-regulate tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE) and activity in monocytes, causing ectodomain shedding of M-CSF receptor, resulting in the disruption of its phosphorylation by M-CSF as well as the induction of osteoclastogenesis from monocytes by M-CSF and RANK ligand. Interestingly, TACE inhibition robustly causes the resumption of the surface expression of M-CSF receptor on monocytes, facilitating M-CSF-mediated phosphorylation of M-CSF receptor and macrophage/OC differentiation while impairing GM-CSF- and IL-4-mediated DC differentiation from monocytes. These results reveal a novel proteolytic regulation of M-CSF receptor expression in monocytes to control M-CSF signaling and monocytic differentiation into macrophage/OC-lineage cells or DCs.

Mycobacteria exploit p38 signaling to affect CD1 expression and lipid antigen presentation by human dendritic cells

Group I CD1 proteins are specialized antigen-presenting molecules that present both microbial and self lipid antigens to CD1-restricted alpha/beta T lymphocytes. The production of high levels of gamma interferon and lysis of infected macrophages by lipid-specific T lymphocytes are believed to play pivotal roles mainly in the defense against mycobacterial infections. We previously demonstrated that Mycobacterium tuberculosis and bacillus Calmette-Guérin (Mycobacterium bovis BCG) induce human monocytes to differentiate into CD1- dendritic cells (DC), which cannot present lipid antigens to specific T cells. Here, we show that in human monocytes mycobacteria trigger phosphorylation of p38 mitogen-activated protein kinase to inhibit CD1 expression in DC derived from infected monocytes. Pretreatment with a specific p38 inhibitor renders monocytes insensitive to mycobacterial subversion and allows them to differentiate into CD1+ DC, which are fully capable of presenting lipid antigens to specific T cells. We also report that one of the pathogen recognition receptors triggered by BCG to activate p38 is complement receptor 3 (CR3), as shown by reduced p38 phosphorylation and partial reestablishment of CD1 membrane expression obtained by CR3 blockade before infection. In conclusion, we propose that p38 signaling is a novel pathway exploited by mycobacteria to affect the expression of CD1 antigen-presenting cells and avoid immune recognition.