Dendritic cells are decreased in blood and accumulated in granuloma in tuberculosis

Therapeutic DNA Vaccine Targeting Mycobacterium tuberculosis Persisters Shortens Curative Tuberculosis Treatment

Mycobacterium tuberculosis ( Mtb) is one of the leading infectious causes of death worldwide. There is no available licensed therapeutic vaccine that shortens active tuberculosis (TB) disease drug treatment and prevents relapse, despite the World Health Organization's calls. Here, we show that an intranasal DNA vaccine containing a fusion of the stringent response rel Mtb gene with the gene encoding the immature dendritic cell-targeting chemokine, MIP-3α/CCL20, shortens the duration of curative TB treatment in immunocompetent mice. Compared to the first-line regimen for drug-susceptible TB alone, our novel adjunctive vaccine induced greater Rel Mtb -specific T-cell responses associated with optimal TB control in spleen, blood, lungs, mediastinal lymph nodes, and bronchoalveolar lavage (BAL) fluid. These responses were sustained, if not augmented, over time. It also triggered more effective dendritic cell recruitment, activation, and colocalization with T cells, implying enhanced crosstalk between innate and adaptive immunity. Moreover, it potentiated a 6-month TB drug-resistant regimen, rendering it effective across treatment regimens, and also showed promising results in CD4+ knockout mice, perhaps due to enhanced Rel-specific CD8+ T-cell responses. Notably, our novel fusion vaccine was also immunogenic in nonhuman primates, the gold standard animal model for TB vaccine studies, eliciting antigen-specific T-cell responses in blood and BAL fluid analogous to those observed in protected mice. Our findings have critical implications for therapeutic TB vaccine clinical development in immunocompetent and immunocompromised populations and may serve as a model for defining immunological correlates of therapeutic vaccine-induced protection.

One sentence summary

A TB vaccine shortens curative drug treatment in mice by eliciting strong TB-protective immune responses and induces similar responses in macaques.

Early innate cell interactions with Mycobacterium tuberculosis in protection and pathology of tuberculosis

Tuberculosis (TB) remains a significant global health challenge, claiming the lives of up to 1.5 million individuals annually. TB is caused by the human pathogen Mycobacterium tuberculosis (Mtb), which primarily infects innate immune cells in the lungs. These immune cells play a critical role in the host defense against Mtb infection, influencing the inflammatory environment in the lungs, and facilitating the development of adaptive immunity. However, Mtb exploits and manipulates innate immune cells, using them as favorable niche for replication. Unfortunately, our understanding of the early interactions between Mtb and innate effector cells remains limited. This review underscores the interactions between Mtb and various innate immune cells, such as macrophages, dendritic cells, granulocytes, NK cells, innate lymphocytes-iNKT and ILCs. In addition, the contribution of alveolar epithelial cell and endothelial cells that constitutes the mucosal barrier in TB immunity will be discussed. Gaining insights into the early cellular basis of immune reactions to Mtb infection is crucial for our understanding of Mtb resistance and disease tolerance mechanisms. We argue that a better understanding of the early host-pathogen interactions could inform on future vaccination approaches and devise intervention strategies.

Mycobacterium tuberculosis induces delayed lipid droplet accumulation in dendritic cells depending on bacterial viability and virulence

Tuberculosis remains a global health threat with high morbidity. Dendritic cells (DCs) participate in the acute and chronic inflammatory responses to Mycobacterium tuberculosis (Mtb) by directing the adaptive immune response and are present in lung granulomas. In macrophages, the interaction of lipid droplets (LDs) with mycobacteria-containing phagosomes is central to host-pathogen interactions. However, the data available for DCs are still a matter of debate. Here, we reported that bone marrow-derived DCs (BMDCs) were susceptible to Mtb infection and replication at similar rate to macrophages. Unlike macrophages, the analysis of gene expression showed that Mtb infection induced a delayed increase in lipid droplet-related genes and proinflammatory response. Hence, LD accumulation has been observed by high-content imaging in late periods. Infection of BMDCs with killed H37Rv demonstrated that LD accumulation depends on Mtb viability. Moreover, infection with the attenuated strains H37Ra and Mycobacterium bovis-BCG induced only an early transient increase in LDs, whereas virulent Mtb also induced delayed LD accumulation. In addition, infection with the BCG strain with the reintroduced virulence RD1 locus induced higher LD accumulation and bacterial replication when compared to parental BCG. Collectively, our data suggest that delayed LD accumulation in DCs is dependent on mycobacterial viability and virulence.

Human Pulmonary Tuberculosis: Understanding the Immune Response in the Bronchoalveolar System

Mycobacterium tuberculosis, the causal agent of one of the most devastating infectious diseases worldwide, can evade or modulate the host immune response and remain dormant for many years. In this review, we focus on identifying the local immune response induced in vivo by M. tuberculosis in the lungs of patients with active tuberculosis by analyzing data from untouched cells from bronchoalveolar lavage fluid (BALF) or exhaled breath condensate (EBC) samples. The most abundant resident cells in patients with active tuberculosis are macrophages and lymphocytes, which facilitate the recruitment of neutrophils. The cellular response is characterized by an inflammatory state and oxidative stress produced mainly by macrophages and T lymphocytes. In the alveolar microenvironment, the levels of cytokines such as interleukins (IL), chemokines, and matrix metalloproteinases (MMP) are increased compared with healthy patients. The production of cytokines such as interferon (IFN)-γ and IL-17 and specific immunoglobulin (Ig) A and G against M. tuberculosis indicate that the adaptive immune response is induced despite the presence of a chronic infection. The role of epithelial cells, the processing and presentation of antigens by macrophages and dendritic cells, as well as the role of tissue-resident memory T cells (Trm) for in situ vaccination remains to be understood.

Pathological and protective roles of dendritic cells in Mycobacterium tuberculosis infection: Interaction between host immune responses and pathogen evasion

Dendritic cells (DCs) are principal defense components that play multifactorial roles in translating innate immune responses to adaptive immunity in Mycobacterium tuberculosis (Mtb) infections. The heterogeneous nature of DC subsets follows their altered functions by interacting with other immune cells, Mtb, and its products, enhancing host defense mechanisms or facilitating pathogen evasion. Thus, a better understanding of the immune responses initiated, promoted, and amplified or inhibited by DCs in Mtb infection is an essential step in developing anti-tuberculosis (TB) control measures, such as host-directed adjunctive therapy and anti-TB vaccines. This review summarizes the recent advances in salient DC subsets, including their phenotypic classification, cytokine profiles, functional alterations according to disease stages and environments, and consequent TB outcomes. A comprehensive overview of the role of DCs from various perspectives enables a deeper understanding of TB pathogenesis and could be useful in developing DC-based vaccines and immunotherapies.

Differential Frequencies of Intermediate Monocyte Subsets Among Individuals Infected With Drug-Sensitive or Drug-Resistant Mycobacterium tuberculosis

The rampant increase in drug-resistant tuberculosis (TB) remains a major challenge not only for treatment management but also for diagnosis, as well as drug design and development. Drug-resistant mycobacteria affect the quality of life owing to the delayed diagnosis and require prolonged treatment with multiple and toxic drugs. The phenotypic modulations defining the immune status of an individual during tuberculosis are well established. The present study aims to explore the phenotypic changes of monocytes & dendritic cells (DC) as well as their subsets across the TB disease spectrum, from latency to drug-sensitive TB (DS-TB) and drug-resistant TB (DR-TB) using traditional immunophenotypic analysis and by uniform manifold approximation and projection (UMAP) analysis. Our results demonstrate changes in frequencies of monocytes (classical, CD14++CD16-, intermediate, CD14++CD16+ and non-classical, CD14+/-CD16++) and dendritic cells (DC) (HLA-DR+CD11c+ myeloid DCs, cross-presenting HLA-DR+CD14-CD141+ myeloid DCs and HLA-DR+CD14-CD16-CD11c-CD123+ plasmacytoid DCs) together with elevated Monocyte to Lymphocyte ratios (MLR)/Neutrophil to Lymphocyte ratios (NLR) and alteration of cytokine levels between DS-TB and DR-TB groups. UMAP analysis revealed significant differential expression of CD14+, CD16+, CD86+ and CD64+ on monocytes and CD123+ on DCs by the DR-TB group. Thus, our study reveals differential monocyte and DC subset frequencies among the various TB disease groups towards modulating the immune responses and will be helpful to understand the pathogenicity driven by Mycobacterium tuberculosis.

Precision Vaccine Development: Cues From Natural Immunity

Traditional vaccine development against infectious diseases has been guided by the overarching aim to generate efficacious vaccines normally indicated by an antibody and/or cellular response that correlates with protection. However, this approach has been shown to be only a partially effective measure, since vaccine- and pathogen-specific immunity may not perfectly overlap. Thus, some vaccine development strategies, normally focused on targeted generation of both antigen specific antibody and T cell responses, resulting in a long-lived heterogenous and stable pool of memory lymphocytes, may benefit from better mimicking the immune response of a natural infection. However, challenges to achieving this goal remain unattended, due to gaps in our understanding of human immunity and full elucidation of infectious pathogenesis. In this review, we describe recent advances in the development of effective vaccines, focusing on how understanding the differences in the immunizing and non-immunizing immune responses to natural infections and corresponding shifts in immune ontogeny are crucial to inform the next generation of infectious disease vaccines.

Differences in host immune populations between rhesus macaques and cynomolgus macaque subspecies in relation to susceptibility to Mycobacterium tuberculosis infection

Rhesus (Macaca mulatta) and cynomolgus (Macaca fasicularis) macaques of distinct genetic origin are understood to vary in susceptibility to Mycobacterium tuberculosis, and therefore differences in their immune systems may account for the differences in disease control. Monocyte:lymphocyte (M:L) ratio has been identified as a risk factor for M. tuberculosis infection and is known to vary between macaque species. We aimed to characterise the constituent monocyte and lymphocyte populations between macaque species, and profile other major immune cell subsets including: CD4+ and CD8+ T-cells, NK-cells, B-cells, monocyte subsets and myeloid dendritic cells. We found immune cell subsets to vary significantly between macaque species. Frequencies of CD4+ and CD8+ T-cells and the CD4:CD8 ratio showed significant separation between species, while myeloid dendritic cells best associated macaque populations by M. tuberculosis susceptibility. A more comprehensive understanding of the immune parameters between macaque species may contribute to the identification of new biomarkers and correlates of protection.

Interplay between alveolar epithelial and dendritic cells and Mycobacterium tuberculosis

The innate response plays a crucial role in the protection against tuberculosis development. Moreover, the initial steps that drive the host-pathogen interaction following Mycobacterium tuberculosis infection are critical for the development of adaptive immune response. As alveolar Mϕs, airway epithelial cells, and dendritic cells can sense the presence of M. tuberculosis and are the first infected cells. These cells secrete mediators, which generate inflammatory signals that drive the differentiation and activation of the T lymphocytes necessary to clear the infection. Throughout this review article, we addressed the interaction between epithelial cells and M. tuberculosis, as well as the interaction between dendritic cells and M. tuberculosis. The understanding of the mechanisms that modulate those interactions is critical to have a complete view of the onset of an infection and may be useful for the development of dendritic cell-based vaccine or immunotherapies.

The immunomodulatory-drug, lenalidomide, sustains and enhances interferon-α production by human plasmacytoid dendritic cells

Background: Lenalidomide (LEN), an immunomodulatory drug (IMiD), is currently used for treatment of multiple myeloma (MM). LEN potentiates T cell and natural killer cell functions. However, the cellular and molecular mechanisms underlying the immunomodulatory effects of LEN remain unclear. We focused on the effects of LEN on human plasmacytoid dendritic cells (pDCs), which are the major source of interferon (IFN)-α in the blood and play a central role in innate immune responses. Results: We found that bortezomib, a proteasome inhibitor used to treat MM, killed pDCs but that 0.1-3 μM LEN (covering clinical plasma concentration range) did not affect pDC survival or CD86 expression. Bortezomib inhibited pDC-derived IFN-α production in a dose-dependent fashion, but 0.1-3 µM LEN sustained pDC-derived IFN-α production when stimulated with an optimal concentration of CpG-ODN 2216 (3 μM). In pDCs stimulated with a low concentration of CpG-ODN (0.1 μM), LEN enhanced IFN-α production. These results indicated that LEN, when used at a clinically relevant concentration, can potentially enhance IFN-α production by pDCs. Conclusion: Collectively, our findings unveiled a novel target of LEN and extend the repertoire of the drug's known immunomodulatory effects. These effects may explain the low incidence of herpes zoster viral infection observed during LEN treatment compared with bortezomib treatment. LEN may function as an IMiD affecting a wide array of immune cells, including pDCs, leading to amplification of a positive immune axis able to eliminate MM cells.

A subset of CD1c+ dendritic cells is increased in patients with tuberculosis and promotes Th17 cell polarization

The role of primary subsets of DCs in Mycobacterium tuberculosis infection in humans is incompletely understood. In this study, we identified a CD1c DC subset with phenotype of CD1c⁺CD11c⁺CD19^-CD11b⁺ that was significantly increased in tuberculous pleural effusions and in peripheral blood from patients with TB compared with that from healthy controls (p < 0.0001). Sputum smear/culture-positive patients with tuberculosis had significantly higher frequency of CD1c⁺CD11b⁺ DC subset than sputum smear/culture-negative patients (p < 0.0001). After effective anti-TB chemotherapy, the frequency of CD1c⁺CD11b⁺ DC subset in peripheral blood and tuberculous pleural effusions was decreased. CD1c⁺CD11b⁺ DC subset from tuberculous pleural effusions expressed higher levels of TLR2, TLR4, CD172a, CD206 and FcεRⅠ, but lower levels of CD80, CD83 and CD86 compared with CD1c⁺CD11b^- DC subset. Expression of IL-1β, IL-6, IL-8, IL-23, TNF-α, IFN-γ and TGF-β mRNA in CD1c⁺CD11b⁺ DCs was higher than in CD1c⁺CD11b^- DC subset. Co-culture of autologous naive CD4⁺ T cells with sorted CD1c⁺CD11b⁺ DCs expressed significantly increased levels of IL-17A and RORγt transcripts as compared with those co-cultured with CD11b^- subset. In conclusion, a CD1c⁺CD11b⁺ DC subset with elevated frequency in patients with tuberculosis was identified and it promoted Th17 cell differentiation.

Blood tolerogenic monocytes and low proportions of dendritic cell subpopulations are hallmarks of human tuberculosis

BACKGROUND

The immune mechanisms underlying the pathogenesis of tuberculosis (TB) need better understanding to improve TB management, as the disease still causes more than 1.5 million deaths annually. This study tested the hypothesis that a modulation of the proportions or activation status of APC during Mycobacterium tuberculosis infection may impact on the course of the disease.

PROCEDURE

Proportions of circulating APC subsets and the expression of stimulatory (CD86), inhibitory (ILT-3, ILT-4, ILT-7), or apoptosis-inducing (PDL-1, PDL-2) molecules were analyzed in 2 independent cohorts, on blood monocytes and dendritic cell (DC) subsets from patients with active or latent TB infection (aTB /LTBI) and from uninfected subjects.

RESULTS

Higher proportions of classical CD14⁺ CD16^- and intermediate CD14⁺ CD16⁺ monocytes, and lower proportions of plasmacytoid DC (pDC) and type 2 myeloid DC were observed in the blood from untreated patients with aTB compared with those with LTBI and with healthy subjects, with an early normalization of the proportions of pDC during treatment. In addition, monocytes from M. tuberculosis-infected subjects expressed higher levels of ILT-3, ILT-4, and PDL-1 compared with healthy controls, these differences being more important for patients with aTB than for those with LTBI.

CONCLUSIONS

These results confirm the hypothesis of a modulation of the proportions and activation status of APC during M. tuberculosis infection and suggest that these cells could play a role in driving the course of M. tuberculosis infection.

Alterations in natural killer and dendritic cell subsets in individuals with HIV-associated neurotuberculosis

One of the commonest HIV-associated opportunistic infections of the central nervous system is neurotuberculosis. Interaction between HIV, Mycobacterium tuberculosis and host immune system in co-infected individuals may result in altered frequencies of immune cells, thereby modulating dissemination and disease progression. We examined the frequencies of natural killer (NK) cell and dendritic cell (DC) subsets in HIV infected individuals with neurotuberculosis (HIVNTB) as compared to individuals with HIV associated systemic TB (HIVSTB), asymptomatic HIV, non-HIV NTB, non-HIV STB, and healthy controls. Peripheral blood mononuclear cells (PBMC) were stained with fluorochrome-conjugated monoclonal antibodies- Lineage cocktail (containing CD3, CD14, CD19, and CD20), HLA-DR, CD16, CD56, CD11c, and CD123, fixed with 2% paraformaldehyde and analyzed on the flow cytometer. The pDCs were significantly reduced in all HIV infected groups, with a marked reduction in HIVNTB cases as compared to healthy controls. While the CD56^- CD16^bt NK cell subset displayed a significant increase in frequency in all three HIV infected groups compared the three HIV negative groups, the CD56^dim CD16^bt subset was significantly lower in frequency in the HIVNTB compared to healthy controls. The decreased frequencies of plasmacytoid DCs and cytotoxic NK cells, which are crucial for innate immune defence against HIV, may result in ineffective virus control and lead to an exacerbated course of disease in HIVNTB individuals.

Profiling dendritic cell subsets in the patients with active pulmonary tuberculosis

Dendritic cell (DC) plays an important role in the immune response against pulmonary tuberculosis. However, the phenotypic profile of DC subsets in peripheral blood in individuals with active pulmonary tuberculosis (APT) is still inconclusive. Here, we demonstrated that the absolute numbers of total DC (tDC), myeloid DC (mDC) and plasmacytoid DC (pDC) in individuals with APT were decreased compared to healthy controls (HCs). The decreased number of DCs, especially of pDC, seems to be a useful diagnostic marker of APT. Meanwhile, the number of DCs was associated with the prolonged/complicated TB, ATD treatment effect and lymphocyte immune reactions, as manifested that relapsed APT patients with a higher number of tDC and lower number of pDC compared to newly diagnosed patients. Interestingly, mDC from APT patients displayed high expressions of CD83 and CCR7, but pDC displayed low expressions of CD83 and CCR7. Moreover, DCs from APT patients expressed lower levels of HLA-DR and CD80, but expressed a higher level of CD86 than those from HCs. However, the antigen uptake capacity of DC subsets was not different between APT and HCs, despite the antigen uptake capacity of pDC was much lower than that of mDC in both APT patients and HCs. Our data represent a systematic profile of DC subsets in the blood of APT patients, and would represent a useful biomarker for APT.

Role of dendritic cells in the pathogenesis of Whipple's disease

Accumulation of Tropheryma whipplei-stuffed macrophages in the duodenum, impaired T. whipplei-specific Th1 responses, and weak secretion of interleukin-12 (IL-12) are hallmarks of classical Whipple's disease (CWD). This study addresses dendritic cell (DC) functionality during CWD. We documented composition, distribution, and functionality of DC ex vivo or after in vitro maturation by fluorescence-activated cell sorting (FACS) and by immunohistochemistry in situ. A decrease in peripheral DC of untreated CWD patients compared to healthy donors was due to reduced CD11c(high) myeloid DC (M-DC). Decreased maturation markers CD83, CD86, and CCR7, as well as low IL-12 production in response to stimulation, disclosed an immature M-DC phenotype. In vitro-generated monocyte-derived DC from CWD patients showed normal maturation and T cell-stimulatory capacity under proinflammatory conditions but produced less IL-12 and failed to activate T. whipplei-specific Th1 cells. In duodenal and lymphoid tissues, T. whipplei was found within immature DC-SIGN(+) DC. DC and proliferating lymphocytes were reduced in lymph nodes of CWD patients compared to levels in controls. Our results indicate that dysfunctional IL-12 production by DC provides suboptimal conditions for priming of T. whipplei-specific T cells during CWD and that immature DC carrying T. whipplei contribute to the dissemination of the bacterium.

Immunity against Mycobacterium tuberculosis and the risk of biologic anti-TNF-α reagents

A third of the world's population is exposed to Mycobacterium tuberculosis in their lifetime. Over eight million people develop a tuberculosis (TB) illness and 1.3 million people die from the disease every year. Acquired immunity (cytotoxic CD8+ T cells (CBT), Th1 CD4+ helper T cells) macrophages, and dendritic cells all play important roles in TB infection. Recently, it is well established that innate immunity as well plays a definitive role in the development of TB immunity under the effects of several cytokines, microbicidal proteins and Toll-like receptors. Meanwhile, the introduction and widespread use of biological disease-modifying anti-rheumatic reagents over the last 15 years worldwide has dramatically advanced and improved the standard care and prognosis of patients with rheumatoid arthritis (RA) and juvenile idiopathic arthritis (JIA). However, as clinical experience with these drugs has grown, the risk of granulomatous infections, especially disseminated TB and fungal infections, has become apparent, especially because having RA or JIA may innately increase the risk of infection (bacterial, viral and fungal). The knowledge of basic immunology has also advanced over the past 10 years and adult and pediatric rheumatologists should increase their understanding of this dynamic between arthritis diseases, anti-TNF-α medications, and TB. This review will provide an up-to-date discussion of both the immunology of the TB organism in the human host and the pathophysiologic mechanisms of the TNF-α blockers in the development of secondary (disseminated) tuberculosis.

Latency-associated protein Acr1 impairs dendritic cell maturation and functionality: a possible mechanism of immune evasion by Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tuberculosis) in latently infected individuals survives and thwarts the attempts of eradication by the immune system. During latency, Acr1 is predominantly expressed by the bacterium. However, whether M. tuberculosis exploits its Acr1 in impairing the host immunity remains widely unexplored. Hence, currently we have investigated the role of Acr1 in influencing the differentiation and function of dendritic cells (DCs), which play a cardinal role in innate and adaptive immunity. Therefore, for the first time, we have revealed a novel mechanism of mycobacterial Acr1 in inhibiting the maturation and differentiation of DCs by inducing tolerogenic phenotype by modulating the expression of PD-L1; Tim-3; indoleamine 2, 3-dioxygenase (IDO); and interleukin 10. Furthermore, Acr1 interferes in the differentiation of DCs by targeting STAT-6 and STAT-3 pathways. Continuous activation of STAT-3 inhibited the translocation of NF-κB in Acr1-treated DCs. Furthermore, Acr1 also augmented the induction of regulatory T cells. These DCs displayed decline in their antigen uptake capacity and reduced ability to help T cells. Interestingly, M. tuberculosis exhibited better survival in Acr1-treated DCs. Thus, this study provides a crucial insight into a strategy adopted by M. tuberculosis to survive in the host by impairing the function of DCs.

A meta-analysis of the association between the CC chemokine ligand 5 (CCL5) -403 G>A gene polymorphism and tuberculosis susceptibility

Aim

Many case-control studies have been performed in the recent past to investigate the association between CCL5 -403 G>A (rs2107538) gene polymorphism and tuberculosis (TB) susceptibility in various ethnic groups. However, these studies have produced inconsistent and contradictory results. In the present study, meta-analysis was performed to assess the association between CCL5 -403 G>A polymorphism and TB risk.

Methodology

Quantitative synthesis was done for the published studies based upon association between CCL5 -403 G>A polymorphism and TB risk from PubMed (Medline), EMBASE web search. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated for allele contrast, homozygous, heterozygous, dominant and recessive genetic models.

Results

A total of six studies comprising 1638 confirmed TB cases and 1519 healthy controls were included in this meta-analysis. Variant A allele (A vs. G: p = 0.035; OR = 1.301, 95% CI = 1.019 to 1.662) and variant homozygous (AA vs. GG; p = 0.001; OR = 1.520, 95% CI = 1.202 to 1.923) carriers were significantly associated with TB susceptibility. Similarly, recessive model (AA vs. GG+GA: p = 0.016; OR = 1.791, 95% CI = 1.117 to 2.873) also indicated increased TB risk. Whereas, heterozygous (GA vs. GG: p = 0.837; OR = 1.028, 95% CI = 0.791 to 1.335) and dominant (AA+GA vs. GG: p = 0.222; OR = 1.188, 95% CI = 0.901 to 1.567) models failed to show increased risk of developing TB.

Conclusions

This meta-analysis suggests that there is a significant association between the CCL5 -403 G>A polymorphism and increased risk of TB. However, larger well-designed epidemiological studies with stratified case control and biological characterization may be helpful to validate this association.

Blood dendritic cell frequency declines in idiopathic Parkinson's disease and is associated with motor symptom severity

The role of inflammation in Parkinson’s Disease (PD) is well appreciated, but its underlying mechanisms are still unclear. Our objective was to determine whether dendritic cells (DC), a unique type of migratory immune cells that regulate immunological response and inflammation have an impact on PD. In a case-control study including 80 PD patients and 80 age- and gender-matched healthy control subjects, the two main blood subsets of plasmacytoid and myeloid DC were defined by flow cytometry analysis. Clinical evaluation of subjects consisting of cognition and depression assessment was performed using the Mini Mental State Examination and the Beck Depression Inventory. The severity of motor symptoms was measured using the Unified Parkinson’s Disease Rating Scale-Part III. Comparison between patient and control DC measures and their relationships with clinical assessments were evaluated.The following main results were obtained: 1) the level of circulating DC (mainly the myeloid subset) was significantly reduced in PD patients in comparison with healthy controls; 2) after controlling for depressive and cognitive characteristics, the frequency of myeloid DC was confirmed as one of the independent determinants of PD; 3) the number of both myeloid and plasmacytoid DC was negatively associated with motor symptom severity. Overall, the decline of blood DC, perhaps due to the recruitment of immune cells to the site of disease-specific lesions, can be considered a clue of the immune alteration that characterizes PD, suggesting innovative exploitations of DC monitoring as a clinically significant tool for PD treatment. Indeed, this study suggests that reduced peripheral blood DC are a pathologically-relevant factor of PD and also displays the urgency to better understand DC role in PD for unraveling the immune system contribution to disease progression and thus favoring the development of innovative therapies ideally based on immunomodulation.

Immune vulnerability of infants to tuberculosis

One of the challenges faced by the infant immune system is learning to distinguish the myriad of foreign but nonthreatening antigens encountered from those expressed by true pathogens. This balance is reflected in the diminished production of proinflammatory cytokines by both innate and adaptive immune cells in the infant. A downside of this bias is that several factors critical for controlling Mycobacterium tuberculosis infection are significantly restricted in infants, including TNF, IL-1, and IL-12. Furthermore, infant T cells are inherently less capable of differentiating into IFN- γ -producing T cells. As a result, infected infants are 5-10 times more likely than adults to develop active tuberculosis (TB) and have higher rates of severe disseminated disease, including miliary TB and meningitis. Infant TB is a fundamentally different disease than TB in immune competent adults. Immunotherapeutics, therefore, should be specifically evaluated in infants before they are routinely employed to treat TB in this age group. Modalities aimed at reducing inflammation, which may be beneficial for adjunctive therapy of some forms of TB in older children and adults, may be of no benefit or even harmful in infants who manifest much less inflammatory disease.

Microbial carriage state of peripheral blood dendritic cells (DCs) in chronic periodontitis influences DC differentiation, atherogenic potential

The low-grade oral infection chronic periodontitis (CP) has been implicated in coronary artery disease risk, but the mechanisms are unclear. In this study, a pathophysiological role for blood dendritic cells (DCs) in systemic dissemination of oral mucosal pathogens to atherosclerotic plaques was investigated in humans. The frequency and microbiome of CD19(-)BDCA-1(+)DC-SIGN(+) blood myeloid DCs (mDCs) were analyzed in CP subjects with or without existing acute coronary syndrome and in healthy controls. FACS analysis revealed a significant increase in blood mDCs in the following order: healthy controls < CP < acute coronary syndrome/CP. Analysis of the blood mDC microbiome by 16S rDNA sequencing showed Porphyromonas gingivalis and other species, including (cultivable) Burkholderia cepacia. The mDC carriage rate with P. gingivalis correlated with oral carriage rate and with serologic exposure to P. gingivalis in CP subjects. Intervention (local debridement) to elicit a bacteremia increased the mDC carriage rate and frequency in vivo. In vitro studies established that P. gingivalis enhanced by 28% the differentiation of monocytes into immature mDCs; moreover, mDCs secreted high levels of matrix metalloproteinase-9 and upregulated C1q, heat shock protein 60, heat shock protein 70, CCR2, and CXCL16 transcripts in response to P. gingivalis in a fimbriae-dependent manner. Moreover, the survival of the anaerobe P. gingivalis under aerobic conditions was enhanced when within mDCs. Immunofluorescence analysis of oral mucosa and atherosclerotic plaques demonstrate infiltration with mDCs, colocalized with P. gingivalis. Our results suggest a role for blood mDCs in harboring and disseminating pathogens from oral mucosa to atherosclerosis plaques, which may provide key signals for mDC differentiation and atherogenic conversion.

The tuberculous granuloma: an unsuccessful host defence mechanism providing a safety shelter for the bacteria?

One of the main features of the immune response to M. Tuberculosis is the formation of an organized structure called granuloma. It consists mainly in the recruitment at the infectious stage of macrophages, highly differentiated cells such as multinucleated giant cells, epithelioid cells and Foamy cells, all these cells being surrounded by a rim of lymphocytes. Although in the first instance the granuloma acts to constrain the infection, some bacilli can actually survive inside these structures for a long time in a dormant state. For some reasons, which are still unclear, the bacilli will reactivate in 10% of the latently infected individuals, escape the granuloma and spread throughout the body, thus giving rise to clinical disease, and are finally disseminated throughout the environment. In this review we examine the process leading to the formation of the granulomatous structures and the different cell types that have been shown to be part of this inflammatory reaction. We also discuss the different in vivo and in vitro models available to study this fascinating immune structure.

Cellular and molecular mechanisms of TSLP function in human allergic disorders--TSLP programs the "Th2 code" in dendritic cells

Thymic stromal lymphopoietin (TSLP) has been recently implicated as a key molecule for initiating allergic inflammation at the epithelial cell-dendritic cell (DC) interface. In humans, aberrant TSLP expression is observed in allergic tissues, such as lesional skins of atopic dermatitis, lungs of asthmatics, nasal mucosa of atopic rhinitis and nasal polyps, and ocular surface of allergic keratoconjunctivitis. TSLP is produced predominantly by damaged epithelial cells and stimulates myeloid DCs (mDCs). TSLP-activated mDCs can promote the differentiation of naïve CD4(+) T cells into a Th2 phenotype and the expansion of CD4(+) Th2 memory cells in a unique manner dependent on OX40L, one of the tumor necrosis factor superfamily members with Th2-promoting function, and lack of production of IL-12. From a genetic point of view, multiple genome-wide association studies have repeatedly identified the TSLP gene as one of the loci associated with susceptibility to allergic diseases. Thus, TSLP is a rational therapeutic target for the treatment of allergic disorders. Elucidating the mechanisms that regulate TSLP expression and the effects of TSLP on orchestrating the immune response toward a Th2 phenotype is essential for developing anti-TSLP therapy.

High TNF-alpha and IL-8 levels predict low blood dendritic cell counts in primary cytomegalovirus infection

BACKGROUND

In vitro studies suggest that human cytomegalovirus (CMV) modulates the functions of dendritic cells (DCs). However, there are limited data on DC homeostasis in CMV-infected patients.

OBJECTIVES

The aim of this study was to characterize circulating DCs and plasma cytokine levels in immunocompetent patients with primary, symptomatic CMV infections.

STUDY DESIGN

The study population consisted of 14 patients suffering of CMV mononucleosis and 14 healthy volunteers (11 CMV-seropositive and 3 CMV-seronegative subjects) included as controls. Peripheral blood mononuclear cells were isolated and used to characterize DCs and to quantify CMV in the blood. Plasma levels of pro-inflammatory and anti-inflammatory cytokines were also measured.

RESULTS

We observed that patients who were developing CMV mononucleosis presented lower myeloid and plasmacytoid DC counts in peripheral blood compared with healthy controls. We also noted elevated levels of inflammatory mediators, of which tumor necrosis factor-α (TNF-α)-which activates DCs and endothelial cells-was the highest. Notably, the decrease in blood DCs correlated with high TNF-α and IL-8 levels by a hyperbolic function.

CONCLUSIONS

Our results suggest that increased levels of inflammatory factors facilitate alterations in DC homeostasis during primary CMV infection, which may contribute to viral-induced modulation of host immunity.

Inflammatory dendritic cells migrate in and out of transplanted chronic mycobacterial granulomas in mice

An estimated one-third of the world's population is infected with Mycobacterium tuberculosis, although most affected individuals maintain a latent infection. This control is attributed to the formation of granulomas, cell masses largely comprising infected macrophages with T cells aggregated around them. Inflammatory DCs, characterized as CD11c+CD11b+Ly6C+, are also found in granulomas and are an essential component of the acute immune response to mycobacteria. However, their function during chronic infection is less well understood. Here, we report that CD11c+ cells dynamically traffic in and out of both acute and chronic granulomas induced by Mycobacterium bovis strain bacillus Calmette-Guérin (BCG) in mice. By transplanting Mycobacterium-induced granulomas containing fluorescently labeled CD11c+ cells and bacteria into unlabeled mice, we were able to follow CD11c+ cell trafficking and T cell activation. We found that half of the CD11c+ cells in chronic granulomas were exchanged within 1 week. Compared with tissue-resident DC populations, CD11c+ cells migrating out of granuloma-containing tissue had an unexpected systemic dissemination pattern. Despite low antigen availability, systemic CD4+ T cell priming still occurred during chronic infection. These data demonstrate that surveillance of granulomatous tissue by CD11c+ cells is continuous and that these cells are distinct from tissue-resident DC populations and support T cell priming during both stages of Mycobacterium infection. This intense DC surveillance may also be a feature of Mycobacterium tuberculosis infection and other granuloma-associated diseases.

Multiscale computational modeling reveals a critical role for TNF-α receptor 1 dynamics in tuberculosis granuloma formation

Multiple immune factors control host responses to Mycobacterium tuberculosis infection, including the formation of granulomas, which are aggregates of immune cells whose function may reflect success or failure of the host to contain infection. One such factor is TNF-α. TNF-α has been experimentally characterized to have the following activities in M. tuberculosis infection: macrophage activation, apoptosis, and chemokine and cytokine production. Availability of TNF-α within a granuloma has been proposed to play a critical role in immunity to M. tuberculosis. However, in vivo measurement of a TNF-α concentration gradient and activities within a granuloma are not experimentally feasible. Further, processes that control TNF-α concentration and activities in a granuloma remain unknown. We developed a multiscale computational model that includes molecular, cellular, and tissue scale events that occur during granuloma formation and maintenance in lung. We use our model to identify processes that regulate TNF-α concentration and cellular behaviors and thus influence the outcome of infection within a granuloma. Our model predicts that TNF-αR1 internalization kinetics play a critical role in infection control within a granuloma, controlling whether there is clearance of bacteria, excessive inflammation, containment of bacteria within a stable granuloma, or uncontrolled growth of bacteria. Our results suggest that there is an interplay between TNF-α and bacterial levels in a granuloma that is controlled by the combined effects of both molecular and cellular scale processes. Finally, our model elucidates processes involved in immunity to M. tuberculosis that may be new targets for therapy.

CCL20 is overexpressed in Mycobacterium tuberculosis-infected monocytes and inhibits the production of reactive oxygen species (ROS)

CCL20 is a chemokine that attracts immature dendritic cells. We show that monocytes, cells characteristic of the innate immune response, infected with Mycobacterium tuberculosis express the CCL20 gene at a much higher level than the same cells infected with non-tuberculous mycobacteria. Interferon (IFN)-γ, a fundamental cytokine in the immune response to tuberculosis, strongly inhibits both the transcription and the translation of CCL20. We have also confirmed that dendritic cells are a suitable host for mycobacteria proliferation, although CCL20 does not seem to influence their intracellular multiplication rate. The chemokine, however, down-regulates the characteristic production of reactive oxygen species (ROS) induced by M. tuberculosis in monocytes, which may affect the activity of the cells. Apoptosis mediated by the mycobacteria, possibly ROS-dependent, was also inhibited by CCL20.

Dendritic cells in chronic mycobacterial granulomas restrict local anti-bacterial T cell response in a murine model

BACKGROUND

Mycobacterium-induced granulomas are the interface between bacteria and host immune response. During acute infection dendritic cells (DCs) are critical for mycobacterial dissemination and activation of protective T cells. However, their role during chronic infection in the granuloma is poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

We report that an inflammatory subset of murine DCs are present in granulomas induced by Mycobacteria bovis strain Bacillus Calmette-guerin (BCG), and both their location in granulomas and costimulatory molecule expression changes throughout infection. By flow cytometric analysis, we found that CD11c(+) cells in chronic granulomas had lower expression of MHCII and co-stimulatory molecules CD40, CD80 and CD86, and higher expression of inhibitory molecules PD-L1 and PD-L2 compared to CD11c(+) cells from acute granulomas. As a consequence of their phenotype, CD11c(+) cells from chronic lesions were unable to support the reactivation of newly-recruited, antigen 85B-specific CD4(+)IFNgamma(+) T cells or induce an IFNgamma response from naïve T cells in vivo and ex vivo. The mechanism of this inhibition involves the PD-1:PD-L signaling pathway, as ex vivo blockade of PD-L1 and PD-L2 restored the ability of isolated CD11c(+) cells from chronic lesions to stimulate a protective IFNgamma T cell response.

CONCLUSIONS/SIGNIFICANCE

Our data suggest that DCs in chronic lesions may facilitate latent infection by down-regulating protective T cell responses, ultimately acting as a shield that promotes mycobacterium survival. This DC shield may explain why mycobacteria are adapted for long-term survival in granulomatous lesions.

Thymic stromal lymphopoietin plays an adjuvant role in BCG-mediated CD8(+) cytotoxic T cell responses through dendritic cell activation

Although Bacillus Calmette-Guérin (BCG) has historically emerged as a potent adjuvant in cancer immunization through dendritic cell (DC) activation, the efficacy of its antitumor effect has been limited. Therefore, the strategy of adjuvant therapy using BCG needs to be improved by adding enhancers. Here we found that thymic stromal lymphopoietin (TSLP) acts as an enhancer for the BCG-mediated antitumor effect. While BCG-stimulated DCs induced CD8(+) T cell production of IFN-gamma without strong cell expansion, TSLP-stimulated DCs induced robust CD8(+) T cell expansion without high quantities of IFN-gamma production. Notably, DCs stimulated with both BCG and TSLP induced robust expansion of CD8(+) T cells that produced a large amount of IFN-gamma with a potent cytolytic activity related to granzyme B expression. Our data suggest that TSLP is a good adjuvant to enhance the BCG-mediated cytotoxic T cell effect through DC activation, and provide a functional basis for a novel strategy for antitumor immune-based therapy.

Disparity in circulating peripheral blood dendritic cell subsets and cytokine profile of pulmonary tuberculosis patients compared with healthy family contacts

Dendritic cell (DC) subsets, myeloid DCs (mDCs), and plasmacytoid DCs (pDCs) play a fundamental role in immune response to Mycobacterium tuberculosis (M. tuberculosis). Flow-cytometric estimation of DC subsets showed differences in the ratio of these subsets in untreated, smear-positive pulmonary tuberculosis patients compared with healthy family contacts (HFC, p < 0.05). The percentage of pDCs (0.14 +/- 0.01) was higher than mDCs (0.12 +/- 0.01) in patients, whereas in HFC, mDCs (0.15 +/- 0.01) was higher than pDCs (0.1 +/- 0.01). The percentage of mDCs (0.15 +/- 0.01) and pDCs (0.11 +/- 0.01) was restored in treated patients. Alteration in the DC subsets before and after chemotherapy was confirmed in the follow-up of acid-fast bacilli (AFB)-positive patients. This reversal in the percentage of mDC vs pDCs implicates the influence of active disease on circulating DC subsets. The cytokine bead array revealed an inverse relationship in the circulating levels of IL-12 and IFN-gamma. High IL-12 (37.9 +/- 15.2) and low IFN-gamma (11.09 +/- 3.6) was seen in HFCs derived serum samples compared with that of patients (p < 0.05). The higher percentage of mDCs and elevated IL-12 levels was found to be associated with high risk HFCs investigated. Furthermore CpG/LPS-stimulated whole-blood culture of untreated patients expressed high IFN-alpha in pDCs and less IL-12 in mDCs compared with those of treated patients.

Human Toll-like receptor 4 polymorphisms TLR4 Asp299Gly and Thr399Ile influence susceptibility and severity of pulmonary tuberculosis in the Asian Indian population

Genetic polymorphisms in Toll-like receptor 4, TLR4 896 A/G (Asp299Gly) and 1196 C/T (Thr399Ile) have been reported to influence TLR4 function and the innate host immune response to mycobacteria. We investigated the effect of these single nucleotide polymorphisms on susceptibility and severity of pulmonary tuberculosis (PTB) in the Asian Indian population. A significantly increased frequency of TLR4 Asp299Gly mutation was observed in the patient group (17%) as compared with healthy controls [8.8%, chi(2) = 10.7, P = 0.001,odds ratio (OR ) = 2.1]. On the other hand, the TLR4 Thr399Ile mutation occurred with comparable frequencies in the two groups (12.6% among patients and 9% in healthy controls). The PTB patients were categorized on the basis of their bacillary load as 3+, 2+, 1+, negative and on the extent of lung involvement as having minimal, moderate, and far-advanced lung disease. The 299Gly mutant occurred in homozygous state (GG) only in patients with high bacillary load (3+) and those with far-advanced lung disease. Similarly, the mutant 399Ile was significantly pronounced in these patients in the homozygous state (TT). The present data suggest that TLR4 substitutions at residues 299 and 399 are associated with pulmonary TB, particularly, the most severe disease.

The role of dendritic cells in mycobacterium-induced granulomas

The presence of dendritic cells (DCs) in mycobacterium-containing granulomas, as well as in other granuloma-inducing diseases, is beginning to be appreciated. This review will summarize what is known about DCs with regards to the granuloma and discuss the potential roles DCs may be playing during mycobacterial infection. Potential functions may include mycobacterial dissemination from lesions or sampling of granuloma-containing mycobacterial antigens and migration to the draining lymph nodes to maintain continuous T cell priming. Additionally, the review will discuss the potential outcomes of DC-T cell cross-talk within the granuloma and whether it results in boosting the effector functions of newly arrived T cells or anergizing systemic T cells locally. Understanding the DCs complex and changing role during this critical stage may help explain how latency is achieved and maintained. Such knowledge might also lead to improved vaccination strategies.

Impairment of monocyte-derived dendritic cells in idiopathic pulmonary arterial hypertension

BACKGROUND AND AIM

With the development of immunology, the role of immune inflammation in idiopathic pulmonary arterial hypertension (IPAH) has attracted interest. Recently, it was discovered that dendritic cells, which are key players in immune inflammation, are implicated in the pathogenesis of IPAH. To elucidate the role of dendritic cells in human IPAH, we compared the changes in the number and immunological function of monocyte-derived dendritic cells (MoDCs) from the peripheral blood of patients with IPAH and healthy controls.

METHODS

The numbers of MoDC subsets (including plasmacytoid dendritic cells (pDCs) and myeloid dendritic cells (mDCs)) in circulating peripheral blood mononuclear cells (PBMCs) was analyzed by flow cytometry, and the concentrations of interleukin (IL)-12, IL-10, and tumor necrosis factor-alpha were measured by enzyme-linked immunosorbent serologic assay kits. The morphology, phenotypic expression, and the ability to stimulate T cell proliferation of MoDCs, cultured from PBMCs in vitro with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4, was analyzed by microscopy, flow cytometry, and MTT assay.

RESULTS

The results of the study are as follows: (1) The number of circulating mDCs was lower in IPAH patients than in controls (0.07 +/- 0.01% to 0.14 +/- 0.02%; p < 0.05). (2) IL-12 levels were higher in IPAH patients than in controls (p < 0.05). (3) MoDCs showed higher expression of CD1a (53.34 +/- 7.43% to 19.29 +/- 7.37%; p < 0.05), and lower expression of costimulatory molecule CD86 (64.54 +/- 5.93% to 87.04 +/- 4.82%; p < 0.05), and less ability to simulate T cell proliferation (when the ratio is 1:10) compared to the controls.

CONCLUSIONS

The study shows that it is possible to obtain typical DCs by culturing PBMCs from patients with IPAH with GM-CSF and IL-4, and it demonstrates that patients with IPAH have a significant change in the number of mDC and a marked immune deficiency of MoDCs.

Clinical response to interferon-beta-1a may be linked to low baseline circulating BDCA1 myeloid dendritic cells Differential role of circulating dendritic cells and CD4+ regulatory T-cells in relapsing-remitting multiple sclerosis: a 1-year longitudinal study

Many variables with association with better response to interferon-beta-1a (IFNbeta-1a) have been described, but none has yet been shown to be predictive of clinical response. In this real-life observational 1-year longitudinal study of 23 relapsing-remitting multiple sclerosis (RRMS) patients treated with subcutaneous IFNbeta-1a, we have shown a lower proportion of circulating myeloid dendritic cells (mDCs) than in healthy controls at baseline. Both univariate (Kaplan-Meier) and multivariate (Cox regression) analyses were conducted to determine which variables (age, sex, baseline EDSS, MS relapse rates 1 year and 2 years before initiating IFNbeta-1a, mDCs and plasmacytoid (pDCs) subsets, activated and regulatory CD4(+) T-cells (T(Reg))) were associated with clinical response to IFNbeta-1a. During 1 year of treatment, we observed a shift towards lower proportions of CD123(+) pDCs expression and higher numbers and function of the T(Reg). Univariate analysis disclosed that MS activity was significantly associated with baseline BDCA1(+) mDCs below < or = 0.4% (p<0.0025). Cox model analysis revealed that baseline BDCA1(+) mDCs was the most closely associated factor with MS activity on IFN treatment during the 1-year follow-up (p<0.01). A better understanding of the rules that govern the T(Reg)-DC relationship will enable scientists to better manage the immune response in MS patients.

The surprising diversity of lipid antigens for CD1-restricted T cells

CD1 proteins have been conserved throughout mammalian evolution and function to present lipid antigens to T cells. Crystal structures of CD1-lipid complexes show that CD1 antigen-binding grooves are composed of four pockets and two antigen entry portals. This structural information now provides a detailed understanding of how CD1-binding grooves capture a surprisingly diverse array of lipid ligands. CD1-expressing APCs are able to acquire lipid antigens from their own pool of lipids and from exogenous sources, including microbial pathogens, bystander cells, or even the systemic circulation. CD1 proteins bind to certain antigens using high stringency loading reactions within endosomes that involve low pH, glycosidases, and lipid transfer proteins. Other antigens can directly load onto CD1 proteins using low stringency mechanisms that are independent of cellular factors. New evidence from in vivo systems shows that CD1-restricted T cells influence outcomes in infectious, autoimmune, and allergic diseases. These studies lead to a broader view of the natural function of alphabeta T cells, which involves recognition of both cellular proteins and lipids.

Synergy between individual TNF-dependent functions determines granuloma performance for controlling Mycobacterium tuberculosis infection

Mycobacterium tuberculosis is one of the world's most deadly human pathogens; an integrated understanding of how it successfully survives in its host is crucial to developing new treatment strategies. One notable characteristic of infection with M. tuberculosis is the formation of granulomas, aggregates of immune cells whose structure and function may reflect success or failure of the host to contain infection. One central regulator of host responses to infection, including granuloma formation, is the pleiotropic cytokine TNF-alpha. Experimental work has characterized roles for TNF in macrophage activation; regulation of apoptosis; chemokine and cytokine production; and regulation of cellular recruitment via transendothelial migration. Separating the effects of these functions is presently difficult or impossible in vivo. To this end, we applied a computational model to understand specific roles of TNF in control of tuberculosis in a single granuloma. In the model, cells are represented as discrete entities on a spatial grid responding to environmental stimuli by following programmed rules determined from published experimental studies. Simulated granulomas emerge as a result of these rules. After confirming the importance of TNF in this model, we assessed the effects of individual TNF functions. The model predicts that multiple TNF activities contribute to control of infection within the granuloma, with macrophage activation as a key effector mechanism for controlling bacterial growth. Results suggest that bacterial numbers are a strong contributing factor to granuloma structure with TNF. Finally, TNF-dependent apoptosis may reduce inflammation at the cost of impairing mycobacterial clearance.

Infection of myeloid dendritic cells with Listeria monocytogenes leads to the suppression of T cell function by multiple inhibitory mechanisms

Myeloid dendritic cells (DC) and macrophages play an important role in pathogen sensing and antimicrobial defense. In this study we provide evidence that myeloid DC respond to infection with Listeria monocytogenes with simultaneous induction of multiple stimulatory and inhibitory molecules. However, the overall impact of infected DC during T cell encounter results in suppression of T cell activation, indicating that inhibitory pathways functionally predominate. Inhibitory activity of infected DC is effected mainly by IL-10 and cyclooxygenase 2-mediated mechanisms, with soluble CD25 acting as an IL-2 scavenger as well as by the products of tryptophan catabolism. These inhibitory pathways are strictly TNF-dependent. In addition to direct infection, DC bearing this regulatory phenotype can be induced in vitro by a combination of signals including TNF, TLR2, and prostaglandin receptor ligation and by supernatants derived from the infected cells. Both infection-associated DC and other in vitro-induced regulatory DC are characterized by increased resistance to infection and enhanced bactericidal activity. Furthermore, myeloid DC expressing multiple regulatory molecules are identified in vivo in granuloma during listeriosis and tuberculosis. Based on the in vivo findings and the study of in vitro models, we propose that in granulomatous infections regulatory DC may possess dual function evolved to protect the host from disseminating infection via inhibition of granuloma destruction by T cells and control of pathogen spreading.

Mycobacterium bovis Bacillus Calmette-Guérin suppresses inflammatory Th2 responses by inducing functional alteration of TSLP-activated dendritic cells

Allergic diseases such as atopic dermatitis and asthma develop as a consequence of dysregulated T(h)2 responses. Recently, it has been demonstrated that interaction between dendritic cells (DCs) and thymic stromal lymphopoietin (TSLP), an IL-7-like cytokine, is essential for evoking T(h)2 responses in allergy. In this study, we investigated whether Mycobacterium bovis Bacillus Calmette-Guérin (BCG), a strong T(h)1 response-inducing adjuvant, can alter the function of DCs activated by TSLP (TSLP-DCs). We demonstrated that BCG redirects TSLP-DCs away from inducing inflammatory T(h)2 cells that produce IL-4, IL-5, IL-13 and tumor necrosis factor (TNF)-alpha and toward regulatory T(h)1 cells that produce IFN-gamma and IL-10. We also demonstrated that this functional alteration of TSLP-DCs by BCG depended on both production of IL-12 from DCs and down-regulation of OX40 ligand, a member of the TNF family, on DCs. These findings suggest that BCG might be a useful adjuvant for the treatment of allergic diseases that are triggered by TSLP.

Peripheral-blood dendritic cells in men with coronary heart disease

Accumulating evidence suggests that an imbalance in T-helper type 1 (Th1)/Th2 response with enhanced Th1 immune response has an important role in the process of coronary artery disease (CAD). Dendritic cell (DC) subsets, myeloid DCs (mDCs) and plasmacytoid DCs (pDCs), could regulate immune reactions by polarizing naive T-helper cells into Th1 or Th2 effector cells. In this study, total peripheral-blood DCs and mDC and pDC subsets were examined in patients with coronary heart disease. Thirty-two men who underwent coronary angiography for chest pain were divided into the CAD group (n = 21) and control group (normal coronary angiographic results, n = 11). Peripheral-blood DCs and DC subsets were detected using a 3-color flow cytometry technique. DCs were defined as Lin1(-)HLA-DR(+); mDCs, as Lin1(-)HLA-DR(+)CD11c(+); and pDCs, as Lin1(-)HLA-DR(+)CD123(+). The absolute number of peripheral-blood DCs was significantly higher in the CAD group compared with the control group (p = 0.04). The mDC fraction in terms of both percentage and absolute number was also significantly increased in the CAD group compared with the control group (all p <0.05), whereas the pDC fraction was similar between the 2 groups (p >0.05). The mDC/pDC ratio was significantly increased in the CAD group than in the control group (p = 0.01). In conclusion, total peripheral-blood DCs are significantly higher in patients with CAD because of an increase in mDC subset, which might contribute to enhanced Th1 response in patients with CAD.

Structures and Functions of Microbial Lipid Antigens Presented by CD1

The CD1 family of proteins has evolved to bind a range of endogenous and foreign lipids and present these at the cell surface for antigen-specific recognition by T cells. The distinct intracellular trafficking pathways of CD 1 molecules indicate that collectively, they have the potential to survey the endocytic system widely for antigen, consistent with a role in the presentation of lipids derived from intracellular microbial pathogens. In keeping with this idea, CDla, CDlb, CDlc and CDld have now been shown to present foreign lipid antigens derived from mycobacteria, Gram-negative bacteria and also protozoan species to T cells. These antigens are extremely diverse chemically, and include naturally occurring lipopeptide, glycolipid and phospholipid structures that are distinct from mammalian lipids. CD1-restricted mycobacterial lipids defined to date derive from the highly complex microbial cell envelope. They play a variety of physiological roles for the microbe, including formation of the plasma membrane and protective cell wall and as metabolic intermediates in iron-scavenging pathways. In each case, alkyl chains of CD 1-restricted lipid antigens are accommodated within a deep hydrophobic groove in the membrane-distal alphal-alpha2 domains of the CD1 molecule, with hydrophilic elements solvent-exposed and accessible for recognition by the T cell receptor. Variation in the number, length and saturation of alkyl chains, and the precise chemistry and chirality of the lipid headgroup, clearly exert dominant influences on antigenicity, mediated by effects on CD1 binding and T cell receptor recognition. In the context of structural studies of CD1-lipid complexes, these data suggest that the CD1 isoforms have evolved binding specificities for different classes of foreign lipids, and strongly support a model for antigen recognition involving fine discrimination of lipid headgroup components by the alpha beta T cell receptor. In this review, we summarise our current knowledge of foreign lipid antigens bound by CD 1, focusing on the roles their distinct structural features play in presentation and T cell antigen recognition, and their likely function in antimicrobial T cell responses.

Study on the function of circulating plasmacytoid dendritic cells in the immunoactive phase of patients with chronic genotype B and C HBV infection

Hepatitis B virus (HBV) infection induces a wide range of chronic liver injury. The mechanism by which HBV evades the immune surveillance system remains obscure. Plasmacytoid dendritic cells (pDCs) seem to be the major endogenous interferon (IFN)-alpha producers and represent one of the most important cell types in the regulation of antiviral innate immunity; however, the phenotype and function of pDCs in patients infected by HBV with different genotypes are yet to be determined. The aim of this study was to investigate the differences in the numbers and function of peripheral blood pDCs in the immune clearing phase of chronic HBV infection with genotypes B and C. Fifty-six patients with persistent HBV infection were included in this study, with 19 age-matched healthy subjects being used as a control group. The frequencies of pDCs were analysed by flow cytometry, and the IFN-alpha produced by peripheral blood mononuclear cells (PBMCs) after stimulation with cytidine phosphate guanosine (CpG) oligonucleotides for 24 h was determined by enzyme-linked immunosorbent assay. The genotypes of HBV were detected by polymerase chain reaction and hybridization. The results showed that the frequency and IFN-alpha-producing capacity of peripheral blood pDCs were dramatically reduced and relatively inversely correlated with the level of serum alanine aminotransferase in both groups of patients with chronic genotype B and C HBV infection. A lower reduction of IFN-alpha production by CpG-stimulated PBMCs was found in patients with genotype C than in those with genotype B in the phase of immune clearance. In conclusion, the frequency and IFN-alpha-producing capacity of peripheral blood pDCs were dramatically reduced in the immunoactive phase of chronic hepatitis B (CHB). Furthermore, the lower reduction in IFN-alpha production in patients with genotype C than in those with genotype B may correlate with the outcome of antiviral treatment in CHB patients and the progression of liver inflammation.

Increased infiltration of intrahepatic DC subsets closely correlate with viral control and liver injury in immune active pediatric patients with chronic hepatitis B

The roles of functionally impaired dendritic cells (DCs) in natural history of chronic hepatitis B (CHB) are unknown. We therefore characterized circulating DC subsets in 15 immune tolerant (IT) and 31 immune active (IA) HBV-infected children. Additionally, intrahepatic DC subsets were also analyzed in 4 IT and 9 IA individuals. The results showed that circulating DC subset numbers were decreased, but the intrahepatic DC counts were concomitantly increased in IA patients versus IT patients or healthy children. This results in the reduction of overall IFN-alpha but not IL-12 production by peripheral blood mononuclear cells of IA patients, although the capacity of single DC in producing cytokines was unchanged in these children. Moreover, there is a significantly inverse correlation of intrahepatic DC subsets with plasma HBV load and a positive correlation with serum ALT levels. These findings suggest that the increased infiltration of intrahepatic DC subsets may participate in the local antiviral immune response in pediatric patients with CHB.

Quantitative and functional differences between peripheral blood myeloid dendritic cells from patients with pleural and parenchymal lung tuberculosis

Dendritic cells (DCs) play a pivotal role in generating protective host immunity to Mycobacterium tuberculosis. Few studies have addressed DC function in the context of active tuberculosis (TB), largely due to technical constraints in obtaining adequate numbers of DC from sick patients. We quantitated peripheral blood myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) in the whole blood of patients with active TB and show that blood from patients with pleural TB was characterized by high circulating levels of mDCs. We also developed and optimized a novel whole-blood assay to study mDC production of the Th1-promoting cytokine interleukin 12 (IL-12) and upregulation of the maturation marker CCR7 after incubation with mycobacteria. We found that pleural TB was associated with increased IL-12 production and CCR7 expression compared to lung parenchymal disease. Our findings suggest important differences in innate immunity between patients with different forms of active TB, and this may contribute to the differences in natural history observed between the two groups.

Decrease in Circulating Myeloid Dendritic Cell Precursors in Coronary Artery Disease

OBJECTIVES

We analyzed the frequency of myeloid dendritic cell (mDC) and plasmacytoid dendritic cell (pDC) precursors in blood of patients with coronary artery disease (CAD) and in atherosclerotic carotid plaques of patients with cerebrovascular disease (CVD).

BACKGROUND

Circulating DC precursors are reduced in several autoimmune diseases. Atherosclerosis has features of an autoimmune disease, such as the presence of autoantibodies or autoreactive T cells. Tissue-resident DCs were previously described in atheromata, and it is assumed that they are important for the activation of T cells against autoantigens there.

METHODS

Circulating mDC and pDC precursors were flow cytometrically detected in healthy controls (n = 19), CAD patients with stable (n = 20) and unstable angina pectoris (n = 19), and acute myocardial infarction (n = 17). In human carotid plaques (n = 65), mDC and pDC precursors were identified immunohistochemically.

RESULTS

Circulating mDC precursors were significantly reduced in patients with stable angina pectoris (0.19%, p = 0.04), unstable angina pectoris (0.16%, p = 0.004), and acute myocardial infarction (0.08%, p < 0.001) compared with control patients (0.22% of peripheral blood mononuclear cells). In contrast, pDC numbers were not significantly altered. Circulating mDC precursors inversely correlated with high-sensitivity C-reactive protein (r = -0.38, p = 0.001) or interleukin-6 (r = -0.42, p < 0.001). In contrast to pDC, significantly more mDC precursors were observed in vulnerable carotid plaques (24, 0.25 mm2; n = 31; p = 0.003) than in stable ones (6.4, 0.25 mm2; n = 34).

CONCLUSIONS

Similar to autoimmune diseases, circulating mDC precursors were significantly reduced in patients with CAD. The emergence of mDC precursors in vulnerable plaques suggests their recruitment into atheromata as a possible reason for their decrease in blood. In contrast, no significant association of circulating pDC precursors with atherosclerosis was observed.

Circulating dendritic cells and interferon-alpha production in patients with tuberculosis: correlation with clinical outcome and treatment response

Dendritic cells (DC) have been characterized recently as having an important role in the initiation and control of immunological response to Mycobacterium tuberculosis infection. Blood DC have been subdivided into myeloid (mDC) and plasmacytoid (pDC) subsets, on the basis of differences in phenotype markers and function. Little is known about the enumeration and functional evaluation of circulating DC in patients with tuberculosis and their correlation with clinical outcome during the course of anti-tuberculous treatment. We assessed circulating mDC and pDC counts measured by a newly developed single-platform flow cytometric assay based on TruCOUNT, as well as the production of interferon (IFN)-alpha after in vitro stimulation by herpes simplex virus (HSV-1) in 24 patients with active tuberculosis (TB) and 37 healthy donors. Absolute numbers of both DC subsets were decreased significantly in patients with active TB compared to controls. Similarly, the production of IFN-alpha was highly impaired. In 13 patients these parameters were assessed longitudinally, before and after the specific anti-microbial treatment. Most interestingly, in all nine patients with successful anti-tuberculous therapy there was a significant and marked increase of pDC counts and IFN-alpha production. In contrast, no significant longitudinal variations in DC counts and IFN-alpha production were observed in four patients with lack of response to specific treatment. In conclusion, active TB is associated with a defect in blood DC numbers and IFN-alpha production that is restored after bacterial clearance and clinical improvement, as a result of effective anti-tuberculous treatment.

Identification of a dendritic cell population in normal testis and in chronically inflamed testis of rats with autoimmune orchitis

Experimental autoimmune orchitis (EAO) in the rat is the primary chronic animal model for the investigation of one of the main causes of male infertility, viz., testicular inflammation. Dendritic cells (DC) are potent antigen-presenting cells that play a fundamental role in autoimmune disease. We investigated the number of DC in normal testis and examined whether DC infiltrated the testis during the development of EAO. EAO was induced by active immunization with testis homogenate and adjuvants in two strains of rat (Wistar and Sprague Dawley). The presence of DC in testis was determined, 50 and 80 days after the first immunization, by immunohistochemical staining with specific antibodies (OX-62 and CD11c), and then the total number of DC was measured by stereological analysis. Labeled cells were found only in the interstitial compartment and within granulomas of EAO animals. The number of DC in EAO testes increased compared with control rats in both strains, whereas the number of OX-62+ and CD11c+ cells in adjuvant controls remained unchanged compared with untreated rats. Interspecies variations in the quantity of DC were found, with the total number of DC per testis in untreated and adjuvant control Sprague-Dawley rats being about three times higher than that seen in Wistar rats. Moreover, the increase in DC numbers at 80 days was less prominent in EAO testes of Sprague-Dawley rats than in the Wistar strain in which EAO was more severe and showed a higher number of granulomae. Thus, we have identified the DC population in normal and chronically inflamed testis. The increase in DC observed in EAO suggests that, under inflammatory conditions, the modified action(s) of these cells is a factor in the induction of the autoimmune response in testis.

Impaired function of dendritic cells circulating in patients infected with hepatitis C virus who have persistently normal alanine aminotransferase levels

Hepatitis C virus (HCV) induces chronic liver disease in hosts which can eventually progresses to liver cirrhosis and hepatocellular carcinoma. However, progression of liver disease is slower in patients with persistently normal levels of alanine aminotransferase (ALT) than in those with active hepatitis. Although distinct immune responses against HCV have been proposed in asymptomatic infection, the role of circulating dendritic cells (DC) in the pathogenesis of these patients remains obscure. To address this issue, we compared the number and function of myeloid DC (MDC) and plasmacytoid DC (PDC) between uninfected individuals and HCV-infected patients with or without elevated ALT levels. Numbers of DC and DC progenitors were significantly lower in patients with chronic active hepatitis than in control subjects. However, no differences were found in the number of DC between normal controls and HCV-infected patients with persistently normal ALT levels. MDC from patients with active hepatitis were less able to polarize naive CD4 T cells into the Th1 phenotype, while their MDC and PDC primed more CD4 T cells producing IL-10 than those from normal controls. Such dysfunction of DC was also observed in patients with persistently normal ALT levels. In conclusion, circulating DC decrease in number predominantly in HCV-infected patients with active hepatitis, and the function of DC is impaired even in those with normal ALT levels.

Immunological control of tuberculosis: role of tumour necrosis factor and more

Therapy of autoimmune diseases with tumour necrosis factor (TNF) neutralising agents has provided a unique opportunity to learn about the significance of TNF in the maintenance of latent bacterial infections in humans. The remarkably high incidence of tuberculosis in patients treated with TNF antagonists raises the intriguing question about the physiological role of TNF in maintaining the lifelong latency of tubercle bacilli in granulomas in infected patients. Basic research during the past decade(s) combined with thoughtful observations in human subjects with tuberculosis and autoimmune diseases has provided several potential explanations for the recurrence of tuberculosis if TNF supply is withdrawn. TNF is involved in at least four key functions that contribute towards beneficial effects on the symptoms of autoimmune disorders on the one hand, and the attenuation of immune responses against Mycobacterium tuberculosis on the other hand. These are outlined in this review: induction of apoptosis, maturation of dendritic cells, activation of antimicrobial activity in macrophages, and orchestration of leucocyte movement.

Longitudinal alteration of circulating dendritic cell subsets and its correlation with steroid treatment in patients with severe acute respiratory syndrome

In this study, we found that 74 patients with severe acute respiratory syndrome (SARS) exhibited a rapid, dramatic decrease in numbers of circulating myeloid and plasmacytoid dendritic cells (mDCs and pDCs) during the first 2 weeks of illness (5.3- and 28.4-fold reductions for mDCs and pDCs compared with 25 healthy individuals, respectively), with slow return to normal cell numbers during convalescence (weeks 5–7 of illness on average). In addition, numbers of circulating CD4 and CD8 T cells exhibited milder reductions (2.1- and 1.8-fold at week 1) and earlier return to normal at a mean of weeks 3 and 4, respectively. A significant inverse correlation was found between numbers of DC and T-cell subsets and high-dose steroid treatment. Our novel findings thus suggest that the acute SARS-coronavirus infection probably contributes to the initial reduction of DC and T-cell subsets in blood, and that high-dose steroid administration may subsequently exacerbate and prolong low expression of the cell subsets. These findings will aid the framing of further studies of the immunopathogenesis of SARS.