Extracellular vesicles from Mycobacterium tuberculosis-infected neutrophils induce maturation of monocyte-derived dendritic cells and activation of antigen-specific Th1 cells

Tuberculosis remains one of the leading public health problems in the world. The mechanisms that lead to the activation of the immune response against Mycobacterium tuberculosis (Mtb) have been extensively studied, with a focus on the role of cytokines as the main signals for immune cell communication. However, less is known about the role of other signals, such as extracellular vesicles (EVs), in the communication between immune cells, particularly during the activation of the adaptive immune response. In this study, we determined that EVs released by human neutrophils infected with Mtb (EV-Mtb) contained several host proteins that are ectosome markers. In addition, we demonstrated that EV-Mtb released after only 30 min of infection carried mycobacterial antigens and pathogen-associated molecular patterns, and we identified 15 mycobacterial proteins that were consistently found in high concentrations in EV-Mtb; these proteins contain epitopes for CD4 T cell activation. We found that EV-Mtb increased the expression of the co-stimulatory molecule CD80 and of the co-inhibitory molecule PD-L1 on immature monocyte-derived dendritic cells. We also found that immature and mature dendritic cells treated with EV-Mtb were able to induce IFN-γ production by autologous Mtb antigen-specific CD4 T cells, indicating that these EVs acted as antigen carriers and transferred mycobacterial proteins to the antigen-presenting cells. Our results provide evidence that EV-Mtb participate in the activation of the adaptive immune response against Mtb.

Indirect Dispersion of SARS-CoV-2 Live-Attenuated Vaccine and Its Contribution to Herd Immunity

It has been 34 months since the beginning of the SARS-CoV-2 coronavirus pandemic, which causes the COVID-19 disease. In several countries, immunization has reached a proportion near what is required to reach herd immunity. Nevertheless, infections and re-infections have been observed even in vaccinated persons. That is because protection conferred by vaccines is not entirely effective against new virus variants. It is unknown how often booster vaccines will be necessary to maintain a good level of protective immunity. Furthermore, many individuals refuse vaccination, and in developing countries, a large proportion of the population has not yet been vaccinated. Some live-attenuated vaccines against SARS-CoV-2 are being developed. Here, we analyze the indirect dispersion of a live-attenuated virus from vaccinated individuals to their contacts and the contribution that this phenomenon could have to reaching Herd Immunity.

IL-6, IL-10, sFas, granulysin and indicators of intestinal permeability as early biomarkers for a fatal outcome in COVID-19

The clinical presentation of coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), ranges between mild respiratory symptoms and a severe disease that shares many of the features of sepsis. Sepsis is a deregulated response to infection that causes life-threatening organ failure. During sepsis, the intestinal epithelial cells are affected, causing an increase in intestinal permeability and allowing microbial translocation from the intestine to the circulation, which exacerbates the inflammatory response. Here we studied patients with moderate, severe and critical COVID-19 by measuring a panel of molecules representative of the innate and adaptive immune responses to SARS-CoV-2, which also reflect the presence of systemic inflammation and the state of the intestinal barrier. We found that non-surviving COVID-19 patients had higher levels of low-affinity anti-RBD IgA antibodies than surviving patients, which may be a response to increased microbial translocation. We identified sFas and granulysin, in addition to IL-6 and IL-10, as possible early biomarkers with high sensitivity (>73 %) and specificity (>51 %) to discriminate between surviving and non-surviving COVID-19 patients. Finally, we found that the microbial metabolite d-lactate and the tight junction regulator zonulin were increased in the serum of patients with severe COVID-19 and in COVID-19 patients with secondary infections, suggesting that increased intestinal permeability may be a source of secondary infections in these patients. COVID-19 patients with secondary infections had higher disease severity and mortality than patients without these infections, indicating that intestinal permeability markers could provide complementary information to the serum cytokines for the early identification of COVID-19 patients with a high risk of a fatal outcome.

Differential activation of innate and adaptive lymphocytes during latent or active infection with Mycobacterium tuberculosis

Most individuals infected with Mycobacterium tuberculosis (Mtb) have latent tuberculosis (TB), which can be diagnosed with tests (like the QuantiFERON test, QFT) that detect the production of IFN-γ by memory T cells in response to the Mtb-specific antigens ESAT-6, CFP-10 and TB7.7. However, the immunological mechanisms that determine if an individual will develop latent or active TB remain incompletely understood. Here we compared the response of innate and adaptive peripheral blood lymphocytes from healthy individuals without Mtb infection (QFT-negative) and from individuals with latent (QFT-positive) or active TB infection, in order to determine the characteristics of these cells that correlate with each condition. In active TB patients, the levels of IFN-γ that were produced in response to Mtb-specific antigens had high positive correlations with IL-1β, TNF-α, MCP-1, IL-6, IL-12p70 and IL-23, while the pro-inflammatory cytokines had high positive correlations between themselves and with IL-12p70 and IL-23. These correlations were not observed in QFT-negative or QFT-positive healthy volunteers. Activation with Mtb soluble extract (a mixture of Mtb antigens and pathogen-associated molecular patterns [PAMPs]) increased the percentage of IFN-γ/IL-17-producing NK cells and of IL-17-producing ILC3 in the peripheral blood of active TB patients, but not of QFT-negative or QFT-positive healthy volunteers. Thus, active TB patients have both adaptive and innate lymphocyte subsets that produce characteristic cytokine profiles in response to Mtb-specific antigens or PAMPs. These profiles are not observed in uninfected individuals or in individuals with latent TB, suggesting that they are a response to active TB infection. This article is protected by copyright. All rights reserved.

Extracellular vesicles released by J774A.1 macrophages reduce the bacterial load in macrophages and in an experimental mouse model of tuberculosis

Background

Tuberculosis is the leading cause of death by an infectious microorganism worldwide. Conventional treatment lasts at least six months and has adverse effects; therefore, it is important to find therapeutic alternatives that reduce the bacterial load and may reduce the treatment duration. The immune response against tuberculosis can be modulated by several mechanisms, including extracellular vesicles (EVs), which are nano-sized membrane-bound structures that constitute an efficient communication mechanism among immune cells.

Methods

The EVs released by the J774A.1 mouse macrophage cell line, both spontaneously (S-EV) and after infection with Mycobacterium tuberculosis H37Rv (Mtb-EV), were purified by ultra-centrifugation and size-exclusion chromatography. The size distribution and chemical composition of these EVs were evaluated, and their effect on the bacterial load and the production of cytokines was determined in both in vitro and in vivo models of M. tuberculosis infection.

Results

Mtb-EV are larger than S-EV, they contain M. tuberculosis-specific antigens (not detected in EVs released from M. fortuitum-infected J774A.1 cells) and are rich in phosphatidylserine, present in their outer membrane layer. S-EV, but not Mtb-EV, reduced the bacterial load and the production of MCP-1 and TNF-α in M. tuberculosis-infected macrophages, and these effects were reversed when phosphatidylserine was blocked with annexin V. Both S-EV and Mtb-EV significantly reduced the lung bacterial load in mice infected with M. tuberculosis after 60 days of treatment, but they had no effect on survival or on the lung pneumonic area of these mice.

Conclusion

J774A.1 macrophages infected with M. tuberculosis H37Rv released EVs that differed in size and phosphatidylserine content from spontaneously released EVs, and these EVs also had different biological effects: S-EV reduced the mycobacterial load and the cytokine production in vitro (through a phosphatidylserine-dependent mechanism), while both EVs reduced the lung bacterial load in vivo. These results are the basis for further experiments to evaluate whether EVs improve the efficiency of the conventional treatment for tuberculosis.

Human platelets and megakaryocytes express defensin alpha 1

Platelets are anucleate cells that have a role in several innate immune functions, including the secretion of proteins with antimicrobial activity. Several studies have demonstrated the ability of platelets to secrete thrombin-induced platelet microbicidal proteins and antimicrobial peptides, like hBD-1. However, the expression and secretion of defensins of the alpha family by platelets have not been fully elucidated. The aim of this study was to characterize the expression of defensin alpha 1 (DEFA1) in human platelets and megakaryocytes. Our data indicate that DEFA1 mRNA and protein are present in peripheral blood platelets and in the megakaryoblastic leukemia cell line (MEG-01). DEFA1 co-localize with α-granules of platelets and MEG-01 cells, and was also detected in cytoplasm of MEG-01 cells. The assay of our in vitro model of platelet-like particles (PLPs) revealed that MEG-01 cells could transfer DEFA1 mRNA to their differentiated PLPs. Furthermore, platelets secreted DEFA1 into the culture medium when activated with thrombin, adenosine diphosphate, and lipopolysaccharide; meanwhile, MEG-01 cells secreted DEFA1 when activated with thrombopoietin. Platelet's secreted DEFA1 can rebind to platelet's surface and have antibacterial activity against the gram-negative bacteria Escherichia coli. In summary, our data indicate that both, human platelets and megakaryocytes, can express and secrete DEFA1. These results suggest a new role of platelets and megakaryocytes in the innate immune response.

Mycobacterium tuberculosis extracellular vesicles induce the formation of granulomalike structures in an in vitro model

Tuberculosis (TB) is an airborne disease caused by Mycobacterium tuberculosis. Only 10% of the infected individuals develop an active disease, while 90% of the infected individuals contain the mycobacteria inside structures known as granulomas, in a latent, asymptomatic state. The lung granuloma is formed by a core of infected macrophages, foam cells and epithelioid macrophages, surrounded by several lymphocyte subsets (CD4 T cells, CD8 T cells, Tγδ cells, NK cells, and B cells). M. tuberculosis releases extracellular vesicles, both spontaneously and under stress conditions; these vesicles carry components, derived from the mycobacterial cell wall, that are ligands for human Toll-like receptors (TLR) 2/6 and 4; as a result, these vesicles activate the innate immune system. To determine if M. tuberculosis extracellular vesicles induce the formation of a granuloma-like structure, we used an in vitro granuloma model, with peripheral blood mononuclear cells from individuals with latent TB (positive for the Quantiferon test). We found that M. tuberculosis extracellular vesicles induced the formation of granuloma-like structures that were similar in numbers, diameters and cellular composition (percentage of monocytes, T cells, Tγδ cells, NK cells and ILCs) to the granuloma-like structures formed in response to live M. tuberculosis H37Rv. These results suggest that M. tuberculosis extracellular vesicles participate in the cellular activation and migration processes that lead to granuloma formation in the lungs of TB patients.

Supported by a grant 20190106 from Secretaría de Investigación y Posgrado, Instituto Politécnico Nacional.

Low Expression of IL-10 in Circulating Bregs and Inverted IL-10/TNF-α Ratio in Tears of Patients with Perennial Allergic Conjunctivitis: A Preliminary Study

Allergic conjunctivitis (AC) is one of the most common ophthalmological disorders seen in clinical practice. Growing evidence from recent years suggests that a subset of IL-10-expressing B cells is involved in inflammatory allergic diseases. In this study, we aimed to evaluate the potential involvement of blood Bregs cells in perennial allergic conjunctivitis (PAC), and interleukins (IL)-1β, IL-6, IL-8, IL-10, and IL-12, and tumor necrosis factor (TNF)-α, were measured in tear samples and compared with healthy controls (HC) using flow cytometry. Non-significant differences in CD19⁺IL-10⁺ cell frequency between PAC patients and healthy controls (HC) were observed. Nevertheless, when we analyzed the mean fluorescence intensity (MFI) of IL-10 on CD19⁺CD38^Lo/Med/Hi-gated cells, we observed a significant decrease in MFI in all Bregs subsets in PAC patients. Additionally, tear cytokines showed 2.8 times lower levels of IL-10 than TNF-α in PAC patients when compared to HC. Our findings demonstrate an immunological dysregulation in patients with allergic conjunctivitis, characterized by the low expression of IL-10 in circulating CD19⁺CD38⁺ Bregs subsets and an inverted tear IL-10/TNF-α ratio, promoting a local pro-inflammatory microenvironment. These findings highlight the novel pathologic changes involved in ocular allergic diseases. Understanding systemic and local mechanisms will aid the design of immunomodulating therapeutics at different levels.

Extracellular Vesicles Released from Mycobacterium tuberculosis-Infected Neutrophils Promote Macrophage Autophagy and Decrease Intracellular Mycobacterial Survival

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis (Mtb). In the lungs, macrophages and neutrophils are the first immune cells that have contact with the infecting mycobacteria. Neutrophils are phagocytic cells that kill microorganisms through several mechanisms, which include the lytic enzymes and antimicrobial peptides that are found in their lysosomes, and the production of reactive oxygen species. Neutrophils also release extracellular vesicles (EVs) (100-1,000 nm in diameter) to the extracellular milieu; these EVs consist of a lipid bilayer surrounding a hydrophilic core and participate in intercellular communication. We previously demonstrated that human neutrophils infected in vitro with Mtb H37Rv release EVs (EV-TB), but the effect of these EVs on other cells relevant for the control of Mtb infection, such as macrophages, has not been completely analyzed. In this study, we characterized the EVs produced by non-stimulated human neutrophils (EV-NS), and the EVs produced by neutrophils stimulated with an activator (PMA), a peptide derived from bacterial proteins (fMLF) or Mtb, and observed that the four EVs differed in their size. Ligands for toll-like receptor (TLR) 2/6 were detected in EV-TB, and these EVs favored a modest increase in the expression of the co-stimulatory molecules CD80, a higher expression of CD86, and the production of higher amounts of TNF-α and IL-6, and of lower amounts of TGF-β, in autologous human macrophages, compared with the other EVs. EV-TB reduced the amount of intracellular Mtb in macrophages, and increased superoxide anion production in these cells. TLR2/6 ligation and superoxide anion production are known inducers of autophagy; accordingly, we found that EV-TB induced higher expression of the autophagy-related marker LC3-II in macrophages, and the co-localization of LC3-II with Mtb inside infected macrophages. The intracellular mycobacterial load increased when autophagy was inhibited with wortmannin in these cells. In conclusion, our results demonstrate that neutrophils produce different EVs in response to diverse activators, and that EV-TB activate macrophages and promote the clearance of intracellular Mtb through early superoxide anion production and autophagy induction, which is a novel role for neutrophil-derived EVs in the immune response to Mtb.

Vanadyl Sulfate Effects on Systemic Profiles of Metabolic Syndrome in Old Rats with Fructose-Induced Obesity

BACKGROUND

Currently, energy obtained from hypercaloric diets has been part of the obesity and type 2 diabetes mellitus (T2DM) epidemics from childhood to old age. Treatment alternatives have been sought from plants, minerals, and trace elements with metabolic effects. Vanadyl sulfate (VS) has been investigated as a hypoglycemic compound in animal and human studies showing effective insulin-mimetic properties. This characteristic encompasses several molecules that have beneficial pleiotropic effects. The aim was to determine the antiobesity, hypoglycemic, and hypolipidemic effects of VS on fructose-induced metabolic syndrome in aged rats.

MATERIAL AND METHODS

Five groups of male Wistar rats were made, each with six rats: two groups with normal diet (ND) and three with high-fructose diet (HFD). The first ND group was treated with saline solution (SS), the second with VS; treatment for HFD groups was in the first group with SS, second with VS, and third with metformin. Weight, body mass index (BMI), blood glucose, and lipidic profile were measured; water, food, fructose and energy consumption were also determined. All parameters were compared among groups.

RESULTS AND DISCUSSION

Although obese rats treated with VS presented anorexia, oligodipsia, and a marked weight loss in the first two weeks. They recovered food and water intake in the third week with a slow recovery of some weight weeks later. VS normalized blood glucose level and decreased triglyceride and insulin levels in obese rats. These results suggest that vanadyl sulfate shows antiobesity, hypoglycemic, and hypolipidemic properties in old obese rats and could be useful as an alternative, additional, and potent preventive treatment for obesity and T2DM control in elderly obese and poorly controlled diabetic patients.

CONCLUSION

VS could play an important role in the treatment of metabolic syndrome, contributing to a decrease in obesity and T2DM, through different ways, such as euglycemia, satiety, weight loss, and lipid profile optimization, among others. However, more research is needed to confirm this suggestion.

CHARACTERIZATION OF INTERFERON-γ PRODUCING CELLS IN THE PERIPHERAL BLOOD OF PATIENTS WITH TUBERCULOSIS

Tuberculosis (TB) caused 1.4 million deaths in 2015. The infection starts when Mycobacterium tuberculosis is inhaled and interacts with immune cells in the respiratory tract. Alveolar macrophages, neutrophils and dendritic cells (DCs) engulf the mycobacteria; these DCs migrate to the draining lymph node and induce the activation of mycobacteria-specific Th cells. These Th cells migrate back to the lung and produce IFNγ and TNFα, two cytokines essential for mycobacterial control. In addition to Th cells, other cells, such as Tγδ and NK cells, produce IFNγ in response to mycobacteria; innate lymphoid cells (ILCs) are also able to produce IFNγ, but it still unknown if ILCs, which have been detected in human lungs during cancer, produce this cytokine in response to mycobacteria.

We evaluated, by flow cytometry, the frequency and IFNγ production of Th, Tγδ, NK and ILCs (ILC1, ILC2 and ILC3) in the peripheral blood of healthy individuals (negative and positive for the Quantiferon [QTF] test, which detects latent TB), and patients with active pulmonary TB. The numbers of Th, Tγδ, NK cells and ILCs (ILC1, ILC2 and ILC3) were decreased in TB patients. Peripheral blood was stimulated with M. tuberculosis soluble extract for 5 h in the presence of brefeldin A. In healthy, QTF-negative individuals, IFNγ production was increased in Tγδ and ILC2 after stimulation; in healthy, QTF-positive individuals, IFNγ production was increased in Th, Tγδ and ILCs, and in TB patients, IFNγ production was increased in NK cells and ILC2. These results suggest ILCs produce IFNγ during TB infection.

This project was funded by SIP-IPN-México (20170616).

Active tuberculosis patients have high levels of IgA anti-alpha-crystallin and isocitrate lyase proteins

SETTING

Mexico City, Mexico.

OBJECTIVE

To identify proteins synthetised by Mycobacterium tuberculosis in hypoxic culture, which resemble more closely a granuloma environment than aerobic culture, and to determine if they are recognised by antibodies from patients with active pulmonary tuberculosis (PTB).

DESIGN

Soluble extracts from M. tuberculosis H37Rv cultured under aerobic or hypoxic conditions were analysed using two-dimensional polyacrylamide gel electrophoresis, and proteins over-expressed under hypoxia were identified by mass spectrometry. The presence of immunoglobulin (Ig) G, IgA and IgM antibodies against these proteins was determined in the serum of 42 patients with active PTB and 42 healthy controls.

RESULTS

We selected three M. tuberculosis H37Rv proteins (alpha-crystallin protein [Acr, Rv2031c], universal stress protein Rv2623 and isocitrate lyase [ICL, RV0467]) that were over-expressed under hypoxia. Titres of anti-Acr and anti-ICL IgA antibodies were higher in patients than in healthy controls, with an area under the receiver operating characteristic curve of 0.71 for anti-ICL IgA antibodies.

CONCLUSION

ICL could be used in combination with other M. tuberculosis antigens to improve the sensitivity and specificity of current serological TB diagnostic methods.

Listeria monocytogenes induces mast cell extracellular traps

Mast cells play an essential role in different immunological phenomena including allergy and infectious diseases. Several bacteria induce mast cell activation leading to degranulation and the production of several cytokines and chemokines. However, mast cells also have different microbicidal activities such as phagocytosis and the release of DNA with embedded granular proteins known as Mast Cell Extracellular Traps (MCETs). Although previous reports indicate that extracellular bacteria are able to induce MCETs little is known if intracellular bacteria can induce these structures. In this work, we evaluated MCETs induction by the intracellular bacteria Listeria monocytogenes. We found that mast cells released DNA after stimulation with L. monocytogenes, and this DNA was complexed to histone and tryptase. Before extracellular DNA release, L. monocytogenes induced modifications to the mast cell nuclear envelope and DNA was detected outside the nucleus. L. monocytogenes stimulated mast cells to produce significant amounts of reactive oxygen species (ROS) and blocking NADPH oxidase diminished DNA release by mast cells. Finally, MCETs showed antimicrobial activity against L. monocytogenes that was partially blocked when β-hexosaminidase activity was inhibited. These results show that L. monocytogenes induces mast cells to produce microbicidal MCETs, suggesting a role for mast cells in containing infection beyond the induction of inflammation.

Mast Cells in Lung Homeostasis: Beyond Type I Hypersensitivity

Lungs are indispensable organs for the respiratory process, and maintaining their homeostasis is essential for human health and survival. However, during the lifetime of an individual, the lungs suffer countless insults that put at risk their delicate organization and function. Many cells of the immune system participate to maintain this equilibrium and to keep functional lungs. Among these cells, mast cells have recently attracted attention because of their ability to rapidly secrete many chemical and biological mediators that modulate different processes like inflammation, angiogenesis, cell proliferation, etc. In this review, we focus on recent advances in the understanding of the role that mast cells play in lung protection during infections, and of the relation of mast cell responses to type I hypersensitivity-associated pathologies. Furthermore, we discuss the potential role of mast cells during wound healing in the lung and its association with lung cancer, and how mast cells could be exploited as therapeutic targets in some diseases

Dialyzable Leukocyte Extracts Activate TLR-2 on Monocytes

Dialyzable leukocyte extracts (DLE) transfer specific cell-mediated immune responses from sensitized donors to non-immune recipients. In addition, DLE have several immunomodulatory effects and are used for the treatment of several infectious and non-infectious diseases. Previous studies showed that human DLE obtained from virus-infected leukocytes and bovine DLE decrease the production of the pro-inflammatory cytokine TNF-α in response to bacterial lipopolysaccharide, in vitro and in vivo. In the present work, we inquire as to whether DLE from uninfected human leukocytes have the ability to regulate cytokine production in peripheral blood mononuclear cells (PBMC) in vitro. We observed that PBMC from healthy individuals were able to produce TNF-α, IL-12 and IL-10 after stimulation with DLE. Moreover, we identified monocytes as the main cell population that produced TNF-α after DLE stimulation. Interestingly, we found that DLE contain unidentified ligands that activate Toll-like receptor (TLR)-2. Finally, we observed that DLE directly activated monocytes through TLR-2. These results reveal a new biological activity of DLE, and suggest that part of the immunomodulatory properties of DLE could be attributed to TLR-2 activation on monocytes and to the induction of a pro-inflammatory environment that is crucial for control of infectious diseases.

Dialyzable leukocyte extracts activate TLR-2 on monocytes

Dialyzable leukocyte extracts (DLE) transfer specific cell-mediated immune responses from sensitized donors to non-immune recipients. In addition, DLE have several immunomodulatory effects and are used for the treatment of several infectious and non-infectious diseases. Previous studies showed that human DLE obtained from virus-infected leukocytes and bovine DLE decrease the production of the pro-inflammatory cytokine TNF-alpha in response to bacterial lipopolysaccharide, in vitro and in vivo. In the present work, we inquire as to whether DLE from uninfected human leukocytes have the ability to regulate cytokine production in peripheral blood mononuclear cells (PBMC) in vitro. We observed that PBMC from healthy individuals were able to produce TNF-alpha, IL-12 and IL-10 after stimulation with DLE. Moreover, we identified monocytes as the main cell population that produced TNF-alpha after DLE stimulation. Interestingly, we found that DLE contain unidentified ligands that activate Toll-like receptor (TLR)-2. Finally, we observed that DLE directly activated monocytes through TLR-2. These results reveal a new biological activity of DLE, and suggest that part of the immunomodulatory properties of DLE could be attributed to TLR-2 activation on monocytes and to the induction of a pro-inflammatory environment that is crucial for control of infectious diseases.

Differential activation of dendritic cells by Mycobacterium tuberculosis Beijing genotype

Mycobacterium tuberculosis (Mtb) inhibits dendritric cells (DC) function in order to delay T cell response. Furthermore, there is increasing evidence that genetic diversity of Mtb strains can affect their interaction with the immune system. Beijing genotype has attracted attention because of its high prevalence and multi-drug resistance. Although it is known that this genotype is hypervirulent and differentially activates macrophages when compared to other genotypes, little is known about its interaction with DC. In order to address this issue, murine bone marrow derived DC (BMDC) were stimulated with soluble extracts (SE) from BCG, H37Rv, Canetti and Beijing genotypes. We observed that unlike other mycobacteria strains, SE-Beijing was unable to induce maturation of DC as assessed by cell surface MHC-II expression. DC stimulated with SE-Beijing failed to produce IL-12 and TNF-α, but did secrete IL-10. Interestingly, SE-Beijing induced CCR7 and PDL-1 on BMDC, but did not induce the expression of CD86. When BMDC stimulated with SE-Beijing were used to activate CD4+ cells they were unable to induce a Th1 response when compared with less virulent genotypes. These results indicate that Beijing is able to modulate DC activation and function, which may be related to the pathogenesis induced by this genotype.

Mycobacterium tuberculosis Beijing genotype induces differential cytokine production by peripheral blood mononuclear cells of healthy BCG vaccinated individuals

Members of the Mycobacterium tuberculosis (Mtb) Beijing genotype are a major concern due to their high prevalence in tuberculosis patients and their high rate of multi-drug resistance. Although it has been shown that Beijing modifies macrophage behavior, little is known about how this genotype could affect the cellular immune response. In order to address this issue, peripheral blood mononuclear cells (PBMC) from healthy BCG vaccinated individuals were stimulated with protein extracts from three Mycobacterium tuberculosis genotypes: Canetti, H37Rv and Beijing evaluating T cell proliferation and cytokine production. In this system both CD4+ and CD8+ proliferated in a similar manner independently of the Mtb genotype used for stimulation. Regarding cytokines, all strains induced similar levels of IFN-γ, but were unable to induce IL-4 and TGF-β. Contrasting, Canetti strain induced lower production of IL-10, TNF-α and IL-12 compared to H37Rv and Beijing. Interestingly, PBMC stimulated with the Beijing strain produced the highest levels of IL-12 and IL-10 than those stimulated with other strains. This differential cytokine expression could affect the pathogenesis induced by Beijing strain through the modulation of inflammatory process in the host, but the precise mechanisms by which this cytokine environment affects the Beijing strain pathogenesis needs further characterization.

Differential pattern of cytokine expression by macrophages infected in vitro with different Mycobacterium tuberculosis genotypes

It has been shown recently that different genotypes of Mycobacterium tuberculosis induce distinct immune responses in the host, as reflected by variations in cytokine and iNOS expression. Because these molecules are probably regulated by multiple factors in vivo this complex phenomenon was partially analysed by assessing cytokine and iNOS expression by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) in an in vitro model of bone marrow-derived macrophages infected with three different M. tuberculosis genotypes: Canetti, H37 Rv and Beijing. Although the three genotypes induced production of iNOS and the different cytokines tested at 24 h post-infection, macrophages infected with the Beijing isolate expressed the highest levels of mRNA for iNOS, interleukin (IL)-1beta, tumour necrosis factor (TNF)-alpha, IL-12 cytokines and lower levels of IL-10 compared with cells infected with other genotypes. This expression pattern has been associated with infection control, but during infection in vivo with the Beijing genotype it is lost upon progression to chronic phase. The failure to control infection is likely to be influenced by cytokines produced by other cell types and bacterial molecules expressed during the course of disease. Results presented in this work show that each genotype has the ability to induce different levels of cytokine expression that could be related to its pathogenesis during infection.

The effect of iron on the expression of cytokines in macrophages infected with Mycobacterium tuberculosis

Iron is known to play an important role in different bacterial infections and, in particular, in their development. One example is infection with Mycobacterium tuberculosis where iron contributes to growth and survival of the bacteria within the host cell. The majority of studies performed on tuberculosis have focused on the direct effect of iron on bacterial growth; however, little is known about how iron modifies the mycobacterial-host interaction. In order to address this, we have investigated the effect of iron on intracellular growth of M. tuberculosis in J774 macrophages and the molecular mechanisms that are affected during this interaction. We observed that iron modifies intracellular growth of the mycobacteria and that their growth kinetics was modified from that observed for the extracellular situation in the presence of iron. Similarly, when iron was present during the infection, there was a reduced release of tumour necrosis factor-alpha and it was related to a higher number of bacilli inside the host cell and low expression of interleukin-1 (IL-1) and IL-6 mRNA. Hence, this work demonstrates that iron, besides promoting mycobacterial growth, also regulates the relationship between macrophage and bacteria.