The diacylated lipopeptide FSL-1 enhances phagocytosis of bacteria by macrophages through a Toll-like receptor 2-mediated signalling pathway

Multi-Faceted Bioactivity Assessment of an Exopolysaccharide from Limosilactobacillus fermentum NCDC400: Antioxidant, Antibacterial, and Immunomodulatory Proficiencies

Exopolysaccharides (EPS) are acknowledged for their diverse functional and technological properties. This study presents the characterization of EPS400, an acidic exopolysaccharide sourced from the native probiotic Limosilactobacillus fermentum NCDC400. Notably, this strain has demonstrated previous capabilities in enhancing dairy food texture and displaying in vivo hypocholesterolemic activity. Our investigation aimed to unveil EPS400's potential biological roles, encompassing antioxidant, antibacterial, and immunomodulatory activities. The results underscore EPS400's prowess in scavenging radicals, including the 2,2-diphenyl-1-picrylhydrazyl radical, 2,2'-azino-di-(3-ethylbenzthiazoline sulfonic acid) radical, superoxide radical, hydroxyl radical, and chelating activity targeting the ferrous ion. Furthermore, EPS400 displayed substantial antibacterial effectiveness against prevalent food spoilage bacteria such as Pseudomonas aeruginosa NCDC105 and Micrococcus luteus. Remarkably, EPS400 exhibited the ability to modulate cytokine production, downregulating pro-inflammatory cytokines TNF-α, IL-1β, IL-6, and nitric oxide, while concurrently promoting the release of anti-inflammatory cytokine IL-10 within lipopolysaccharide-activated murine primary macrophages. Additionally, EPS400 significantly (p ≤ 0.05) enhanced the phagocytic potential of macrophages. Collectively, our findings spotlight EPS400 as a promising contender endowed with significant antioxidant, antibacterial, and immunomodulatory attributes. These characteristics propose EPS400 as a potential pharmaceutical or bioactive component, with potential applications in the realm of functional food development.

Glycolipid-enriched fraction of Osmanthus fragrans inhibits LPS-induced expression of inflammatory genes, COX-2, E-selectin, and Interleukin-8

ETHNOPHARMACOLOGICAL RELEVANCE

Osmanthus fragrans Lour. is a small ornamental tree native to the Southeastern parts of China. It is mainly cultivated because of its characteristic fragrance, and used in the food and perfume industry. Besides, its flowers are used in traditional Chinese medicine to treat a variety of diseases including those related to inflammation.

AIM OF THE STUDY

The aim of the study was to investigate in more detail the anti-inflammatory properties of O. fragrans flowers, and to characterize their active principles and mechanisms of action.

MATERIALS AND METHODS

O. fragrans flowers were successively extracted with n-hexane, dichloromethane and methanol. The extracts were further fractionated by chromatographic separation. COX-2 mRNA expression in PMA-differentiated, LPS-stimulated THP-1 cells was used as lead assay for activity-guided fractionation. The most potent fraction was chemically analyzed by LC-HRMS. The pharmacological activity was also evaluated in other inflammation-related in-vitro models, such as analysis of IL-8 secretion and E-selectin expression in HUVECtert cells and selective inhibition of COX-isoenzymes.

RESULTS

n-Hexane and dichloromethane extracts of O. fragrans flowers significantly inhibited COX-2 (PTGS2) mRNA expression. Additionally, both extracts inhibited COX-2 enzyme activity, whereas COX-1 enzyme activity was affected to a significantly lower extent. Fractionation of the extracts led to a highly active, glycolipid-containing fraction. In total, 10 glycolipids were tentatively annotated by LC-HRMS. This fraction also inhibited LPS-induced COX-2 mRNA expression, IL-8 secretion and E-selectin expression. The effects were limited to LPS-induced inflammation and not observed when inflammatory genes were induced by TNF-α, IL-1β or FSL-1. Since all these inducers of inflammation act via different receptors, it is likely that the fraction interferes with the binding of LPS to the TLR4-receptor, which mediates pro-inflammatory effects of LPS.

CONCLUSION

Taken together, the results demonstrate the anti-inflammatory potential of O. fragrans flower extracts in general, and of the glycolipid-enriched fraction in particular. The effects of glycolipid-enriched fraction are potentially mediated via the inhibition of the TLR4 receptor complex.

Microbial Lipopeptides: Properties, Mechanics and Engineering for Novel Lipopeptides

Microorganisms produce active surface agents called lipopeptides (LPs) which are amphiphilic in nature. They are cyclic or linear compounds and are predominantly isolated from Bacillus and Pseudomonas species. LPs show antimicrobial activity towards various plant pathogens and act by inhibiting the growth of these organisms. Several mechanisms are exhibited by LPs, such as cell membrane disruption, biofilm production, induced systematic resistance, improving plant growth, inhibition of spores, etc., making them suitable as biocontrol agents and highly advantageous for industrial utilization. The biosynthesis of lipopeptides involves large multimodular enzymes referred to as non-ribosomal peptide synthases. These enzymes unveil a broad range of engineering approaches through which lipopeptides can be overproduced and new LPs can be generated asserting high efficacy. Such approaches involve several synthetic biology systems and metabolic engineering techniques such as promotor engineering, enhanced precursor availability, condensation domain engineering, and adenylation domain engineering. Finally, this review provides an update of the applications of lipopeptides in various fields.

Pushing the envelope: Immune mechanism and application landscape of macrophage-activating lipopeptide-2

Mycoplasma fermentans can cause respiratory diseases, arthritis, genitourinary tract infections, and chronic fatigue syndrome and have been linked to the development of the human immunodeficiency virus. Because mycoplasma lacks a cell wall, its outer membrane lipoproteins are one of the main factors that induce inflammation in the organism and contribute to disease development. Macrophage-activating lipopeptide-2 (MALP-2) modulates the inflammatory response of monocytes/macrophages in a bidirectional fashion, indirectly enhances the cytotoxicity of NK cells, promotes oxidative bursts in neutrophils, upregulates surface markers on lymphocytes, enhances antigen presentation on dendritic cells and induces immune inflammatory responses in sebocytes and mesenchymal cells. MALP-2 is a promising vaccine adjuvant for this application. It also promotes vascular healing and regeneration, accelerates wound and bone healing, suppresses tumors and metastasis, and reduces lung infections and inflammation. MALP-2 has a simple structure, is easy to synthesize, and has promising prospects for clinical application. Therefore, this paper reviews the mechanisms of MALP-2 activation in immune cells, focusing on the application of MALP-2 in animals/humans to provide a basis for the study of pathogenesis in Mycoplasma fermentans and the translation of MALP-2 into clinical applications.

The Influence of Antibiotic Resistance on Innate Immune Responses to Staphylococcus aureus Infection

Staphylococcus aureus (S. aureus) causes a broad range of infections and is associated with significant morbidity and mortality. S. aureus produces a diverse range of cellular and extracellular factors responsible for its invasiveness and ability to resist immune attack. In recent years, increasing resistance to last-line anti-staphylococcal antibiotics daptomycin and vancomycin has been observed. Resistant strains of S. aureus are highly efficient in invading a variety of professional and nonprofessional phagocytes and are able to survive inside host cells. Eliciting immune protection against antibiotic-resistant S. aureus infection is a global challenge, requiring both innate and adaptive immune effector mechanisms. Dendritic cells (DC), which sit at the interface between innate and adaptive immune responses, are central to the induction of immune protection against S. aureus. However, it has been observed that S. aureus has the capacity to develop further antibiotic resistance and acquire increased resistance to immunological recognition by the innate immune system. In this article, we review the strategies utilised by S. aureus to circumvent antibiotic and innate immune responses, especially the interaction between S. aureus and DC, focusing on how this relationship is perturbed with the development of antibiotic resistance.

Mycobacterium tuberculosis PPE18 protein inhibits MHC class II antigen presentation and B cell response in mice

PPE18 protein belongs to PE/PPE family of Mycobacterium tuberculosis. We reported earlier that PPE18 protein provides survival advantage to M. tuberculosis during infection. In the current study, we found that PPE18 inhibits MHC class II-mediated antigen presentation by macrophages in a dose-dependent manner without affecting the surface level of MHC class II or co-stimulatory molecules. PPE18 does not affect antigen uptake or presentation of preprocessed peptide by macrophages. Antigen degradation was found to be inhibited by PPE18 protein due to perturbation in phagolysosomal acidification. PPE18-mediated inhibition of MHC class II antigen presentation caused poorer activation of CD4 T cells. Mice infected with M. smegmatis expressing PPE18 exhibited reduced maturation and activation of B cells and had decreased Mycobacteria-specific antibody titers. Thus M. tuberculosis probably utilizes PPE18 to inhibit MHC class II antigen presentation causing poorer activation of adaptive immune responses. This study may be useful in understanding host-pathogen interaction and open up directions of designing novel therapeutics targeting PPE18 to tackle this nefarious pathogen.

March of Mycobacterium: miRNAs intercept host cell CD40 signalling

The disease tuberculosis is fatal if untreated. It is caused by the acid-fast bacilli Mycobacterium tuberculosis. Mycobacterium resides and replicates within the alveolar macrophages, causing inflammation and granuloma, wherein macrophage-T cell interactions enhance the inflammation-causing pulmonary caseous lesions. The first interactions between Mycobacterium and the receptors on macrophages decide the fate of Mycobacterium because of phagolysosomal impairments and the expression of several miRNAs, which may regulate CD40 expression on macrophages. While the altered phagolysosomal functions impede antigen presentation to the T cell-expressed antigen receptor, the interactions between the macrophage-expressed CD40 and the T cell-expressed CD40-ligand (CD40L or CD154) provide signals to T cells and Mycobacterium-infected macrophages. These two functions significantly influence the resolution or persistence of Mycobacterium infection. CD40 controls T-cell polarisation and host-protective immunity by eliciting interleukin-12p40, nitric oxide, reactive oxygen species and IFN-γ production. Indeed, CD40-deficient mice succumb to low-dose aerosol infection with Mycobacterium because of deficient interleukin (IL)-12 production leading to impaired IFN-γ-secreting T-cell response. In contrast, despite generating fewer granulomas, the CD40L-deficient mice developed anti-mycobacterial T-cell responses to the levels observed in the wild-type mice. These host-protective responses are significantly subdued by the Mycobacterium-infected macrophage produced TGF-β and IL-10, which promote pro-mycobacterial T-cell responses. The CD40-CD40L-induced counteractive immune responses against Mycobacterium thus present a conundrum that we explain here with a reconciliatory hypothesis. Experimental validation of the hypothesis will provide a rationale for designing anti-tubercular immunotherapy.

Endo-1,3(4)-β-Glucanase-Treatment of Oat β-Glucan Enhances Fermentability by Infant Fecal Microbiota, Stimulates Dectin-1 Activation and Attenuates Inflammatory Responses in Immature Dendritic Cells

Background: Non-digestible carbohydrates are added to infant formula to mimic the effects of human milk oligosaccharide by acting as prebiotics and stimulating the immune system. Although not yet used in infant formulas, β-glucans are known to have beneficial health effects, and are therefore of potential interest for supplementation. Methods and results: We investigated the in vitro fermentation of native and endo-1,3(4)-β-glucanase-treated oat β-glucan using pooled fecal inocula of 2- and 8-week-old infants. While native oat β-glucan was not utilized, both inocula specifically utilized oat β-glucan oligomers containing β(1→4)-linkages formed upon enzyme treatment. The fermentation rate was highest in the fecal microbiota of 2-week-old infants, and correlated with a high lactate production. Fermentation of media supplemented with native and enzyme-treated oat β-glucans increased the relative abundance of Enterococcus and attenuated pro-inflammatory cytokine production (IL-1β, IL-6, TNFα) in immature dendritic cells. This attenuating effect was more pronounced after enzyme treatment. This attenuation might result from the enhanced ability of fermented oat β-glucan to stimulate Dectin-1 receptors. Conclusion: Our findings demonstrate that endo-1,3(4)-β-glucanase treatment enhances the fermentability of oat β-glucan and attenuates pro-inflammatory responses. Hence, this study shows that especially enzyme-treated oat β-glucans have a high potential for supplementation of infant formula.

TLR2/CXCR4 coassociation facilitatesChlamydia pneumoniaeinfection-induced atherosclerosis

Toll-like receptor 2 (TLR2) and C-X-C motif chemokine receptor 4 (CXCR4) have both been shown to be involved in atherosclerosis. We demonstrate for the first time the presence of TLR2/CXCR4 coassociation during C. pneumoniae infection-induced atherosclerosis. Amazingly, blocking of both TLR2 and CXCR4 significantly retards and even almost reverses this infection-induced atherosclerosis. Our work reveals new mechanisms about C. pneumoniae infection-induced atherosclerosis and identifies potential new therapeutic targets for the prevention and treatment of atherosclerosis.

Toll-Like Receptor 2 and Lipoprotein-Like Lipoproteins Enhance Staphylococcus aureus Invasion in Epithelial Cells

Staphylococcus aureus contains a certain subclass of lipoproteins, the so-called lipoprotein-like lipoproteins (Lpl's), that not only represent Toll-like receptor 2 (TLR2) ligands but are also involved in host cell invasion. Here we addressed the question of which factors contribute to Lpl-mediated invasion of epithelial cells and keratinocytes. For this purpose, we compared the invasiveness of USA300 and its Δlpl mutant under different conditions. In the presence of the matrix proteins IgG, fibrinogen (Fg), and fibronectin (Fn), and of fetal bovine serum (FBS), the invasion ratio was increased in both strains, and always more in USA300 than in its Δlpl mutant. Interestingly, when we compared the invasion of HEK-0 and HEK-TLR2 cells, the cells expressing TLR2 showed a 9-times-higher invasion frequency. When HEK-TLR2 cells were additionally stimulated with a synthetic lipopeptide, Pam₃CSK₄ (P3C), the invasion frequency was further increased. A potential reason for the positive effect of TLR2 on invasion could be that TLR2 activation by P3C also activates F-actin formation. Here we show that S. aureus invasion depends on a number of factors, on the host side as well as on the bacterial side.

The Toll-Like Receptor 2/6 Agonist, FSL-1 Lipopeptide, Therapeutically Mitigates Acute Radiation Syndrome

Risks of radiation exposure from nuclear incidents and cancer radiotherapy are undeniable realities. These dangers urgently compel the development of agents for ameliorating radiation–induced injuries. Biologic pathways mediated by myeloid differentiation primary response gene 88 (MyD88), the common adaptor for toll–like receptor (TLR) and Interleukin–1 receptor signaling, are critical for radioprotection. Treating with agonists prior to radiation enhances survival by activating TLR signaling, whereas radiomitigating TLR–activating therapeutics given after exposure are less defined. We examine the radiomitigation capability of TLR agonists and identify one that is superior for its efficacy and reduced toxic consequences compared to other tested agonists. We demonstrate that the synthetic TLR2/6 ligand Fibroblast–stimulating lipopeptide (FSL–1) substantially prolongs survival in both male and female mice when administered 24 hours after radiation and shows MyD88–dependent function. FSL–1 treatment results in accelerated hematopoiesis in bone marrow, spleen and periphery, and augments systemic levels of hematopoiesis–stimulating factors. The ability of FSL–1 to stimulate hematopoiesis is critical, as hematopoietic dysfunction results from a range of ionizing radiation doses. The efficacy of a single FSL–1 dose for alleviating radiation injury while protecting against adverse effects reveals a viable radiation countermeasures agent.

THP-1 and human peripheral blood mononuclear cell-derived macrophages differ in their capacity to polarize in vitro

Macrophages (Mφ) undergo activation to pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes in response to pathophysiologic stimuli and dysregulation of the M1-M2 balance is often associated with diseases. Therefore, studying mechanisms of macrophage polarization may reveal new drug targets. Human Mφ polarization is generally studied in primary monocyte-derived Mφ (PBMC Mφ) and THP-1-derived Mφ (THP-1 Mφ). We compared the polarization profile of THP-1 Mφ with that of PBMC Mφ to assess the alternative use of THP-1 for polarization studies. Cellular morphology, the expression profiles of 18 genes and 4 cell surface proteins, and phagocytosis capacity for apoptotic cells and S. aureus bioparticles were compared between these Mφ, activated towards M1, M2a, or M2c subsets by stimulation with LPS/IFNγ, IL-4, or IL-10, respectively, for 6h, 24h and 48h. The Mφ types are unique in morphology and basal expression of polarization marker genes, particularly CCL22, in a pre-polarized state, and were differentially sensitive to polarization stimuli. Generally, M1 markers were instantly induced and gradually decreased, while M2 markers were markedly expressed at a later time. Expression profiles of M1 markers were similar between the polarized Mφ types, but M2a cell surface markers demonstrated an IL-4-dependent upregulation only in PBMC Mφ. Polarized THP-1 Mφ but not PBMC Mφ showed distinctive phagocytic capacity for apoptotic cells and bacterial antigens, respectively. In conclusion, our data suggest that THP-1 may be useful for performing studies involving phagocytosis and M1 polarization, rather than M2 polarization.

TLR2 activation induces antioxidant defence in human monocyte-macrophage cell line models

When monocytes are recruited to inflammation/infection sites, extravasate and differentiate into macrophages, they encounter increasing levels of oxidative stress, both from exogenous and endogenous sources. In this study, we aimed to determine whether there are specific biochemical mechanisms responsible for an increase in oxidative stress resistance in differentiating macrophages. We performed experiments on in vitro cell line models of the monocyte-macrophage differentiation axis (less differentiated THP-1 cells and more differentiated Mono Mac 6 cells). At the same time, we verified the hypothesis that activating monocyte/macrophage innate immune response by pathogens (exemplified by stimulating the TLR2 pattern recognition receptor) would further strengthen cellular antioxidant defences. We found that resistance to exogenous oxidative stress increased substantially both during differentiation and upon activation of TLR2. This increase in antioxidant resistance was accompanied by decrease in free radical damage to cellular proteins. On the molecular level, this resistance was mediated especially by increased levels and activity of glutathione, glutathione-related antioxidant enzymes and Mn superoxide dismutase, as shown by gene expression assays, Western blotting and enzyme activity assays. Moreover, upon TLR2 activation additional molecular mechanisms came into play, conferring additional resistance levels even upon differentiated macrophage-like cells, mainly related to thioredoxin-linked antioxidant enzymes.

Sodium Octanoate Modulates the Innate Immune Response of Bovine Mammary Epithelial Cells through the TLR2/P38/JNK/ERK1/2 Pathway: Implications during Staphylococcus aureus Internalization

Bovine mammary epithelial cells (bMECs) contribute to mammary gland defense against invading pathogens, such as Staphylococcus aureus (intracellular facultative), which is recognized by TLR2. In a previous report, we showed that sodium octanoate [NaO, a medium chain fatty acid (C8)] induces (0.25 mM) or inhibits (1 mM) S. aureus internalization into bMECs and differentially regulates the innate immune response (IIR). However, the molecular mechanisms have not been described, which was the aim of this study. The results showed that α5β1 integrin membrane abundance (MA) was increased in 0.25 mM NaO-treated cells, but TLR2 or CD36 MA was not modified. When these receptors were blocked individually, 0.25 mM NaO-increased S. aureus internalization was notably reduced. Interestingly, in this condition, the IIR of the bMECs was impaired because MAPK (p38, JNK, and ERK1/2) phosphorylation and the activation of transcription factors related to these pathways were decreased. In addition, the 1 mM NaO treatment induced TLR2 MA, but neither the integrin nor CD36 MA was modified. The reduction in S. aureus internalization induced by 1 mM NaO was increased further when TLR2 was blocked. In addition, the phosphorylation levels of the MAPKs increased, and 13 transcriptional factors related to the IIR were slightly activated (CBF, CDP, c-Myb, AP-1, Ets-1/Pea-3, FAST-1, GAS/ISRE, AP-2, NFAT-1, OCT-1, RAR/DR-5, RXR/DR-1, and Stat-3). Moreover, the 1 mM NaO treatment up-regulated gene expression of IL-8 and RANTES and secretion of IL-1β. Notably, when 1 mM NaO-treated bMECs were challenged with S. aureus, the gene expression of IL-8 and IL-10 increased, while IL-1β secretion was reduced. In conclusion, our results showed that α5β1 integrin, TLR2 and CD36 are involved in 0.25 mM NaO-increased S. aureus internalization in bMECs. In addition, 1 mM NaO activates bMECs via the TLR2 signaling pathways (p38, JNK, and ERK1/2), which improves IIR before S. aureus invasion. Additionally, NaO (1 mM) might exert anti-inflammatory effects after bacterial internalization.

Phagocytosis Enhances Lysosomal and Bactericidal Properties by Activating the Transcription Factor TFEB

Macrophages internalize pathogens through phagocytosis, entrapping them into organelles called phagosomes. Phagosomes then fuse with lysosomes to mature into phagolysosomes, acquiring an acidic and hydrolytic lumen that kills the pathogens. During an ongoing infection, macrophages can internalize dozens of bacteria. Thus, we hypothesized that an initial round of phagocytosis might boost lysosome function and bactericidal ability to cope with subsequent rounds of phagocytosis. To test this hypothesis, we employed Fcγ-receptor-mediated phagocytosis and endocytosis, which internalize immunoglobulin G (IgG)-opsonized particles and polyvalent IgG immune complexes, respectively. We report that Fcγ receptor activation in macrophages enhances lysosome-based proteolysis and killing of subsequently phagocytosed E. coli compared to naive macrophages. Importantly, we show that Fcγ receptor activation causes nuclear translocation of TFEB, a transcription factor that boosts expression of lysosome genes. Indeed, Fc receptor activation is accompanied by increased expression of specific lysosomal proteins. Remarkably, TFEB silencing represses the Fcγ-receptor-mediated enhancements in degradation and bacterial killing. In addition, nuclear translocation of TFEB requires phagosome completion and fails to occur in cells silenced for MCOLN1, a lysosomal Ca(2+) channel, suggesting that lysosomal Ca(2+) released during phagosome maturation activates TFEB. Finally, we demonstrate that non-opsonic phagocytosis of E. coli also enhances lysosomal degradation in a TFEB-dependent manner, suggesting that this phenomenon is not limited to Fcγ receptors. Overall, we show that macrophages become better killers after one round of phagocytosis and suggest that phagosomes and lysosomes are capable of bi-directional signaling.

Differential induction of inflammatory cytokines and reactive oxygen species in murine peritoneal macrophages and resident fresh bone marrow cells by acute staphylococcus aureus infection: contribution of toll-like receptor 2 (TLR2)

Among the known Toll-like receptors (TLRs), Toll-like receptor 2 (TLR2) is a key sensor for detecting Staphylococcus aureus invasion. But the function of TLR2 during S. aureus infection in different cell populations is unclear. Two different cell subtypes were chosen to study the interaction of S. aureus with TLR2 because macrophages are extremely different from one compartment to another and their capacity to respond to live bacteria or bacterial products differs from one site to another. The contribution of TLR2 to the host innate response against acute live S. aureus infection and heat-killed S. aureus (HKSA) using anti-TLR2 antibody in murine peritoneal macrophages and resident fresh bone marrow cells has been investigated here. TLR2 blocking before infection induces the release of interleukin (IL)-10 by macrophages thereby inhibiting excessive production of oxidants by activating antioxidant enzymes. TLR2-blocked peritoneal macrophages showed impaired release of tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ) and IL-6 in response to both live and heat-killed S. aureus infection except bone marrow cells. TLR2-mediated free radical production and killing of S. aureus were modulated by TLR2 blocking in peritoneal macrophages and resident bone marrow cells. This study supported that S. aureus persists in resident bone marrow cells in a state of quiescence.

The activation of the TLR2/p38 pathway by sodium butyrate in bovine mammary epithelial cells is involved in the reduction of Staphylococcus aureus internalization

Staphylococcus aureus is an etiological agent of human and animal diseases, and it is able to internalize into non-professional phagocytic cells (i.e. bovine mammary epithelial cells, bMECs), which is an event that is related to chronic and recurrent infections. bMECs contribute to host innate immune responses (IIR) through TLR pathogen recognition, whereby TLR2 is the most relevant for S. aureus. In a previous report, we showed that sodium butyrate (NaB, 0.5mM), which is a short chain fatty acid (SCFA), reduced S. aureus internalization into bMECs by modulating their IIR. However, the molecular mechanism of this process has not been described, which was the aim of this study. The results showed that the TLR2 membrane abundance (MA) and mRNA expression were induced by 0.5mM NaB ∼1.6-fold and ∼1.7-fold, respectively. Additionally, 0.5mM NaB induced p38 phosphorylation, but not JNK1/2 or ERK1/2 phosphorylation in bMECs, which reached the baseline when the bMECs were S. aureus-challenged. Additionally, bMECs that were treated with 0.5mM NaB (24h) showed activation of 8 transcriptional factors (AP-1, E2F-1, FAST-1, MEF-1, EGR, PPAR, ER and CBF), which were partially reverted when the bMECs were S. aureus-challenged. Additionally, 0.5mM NaB (24h) up-regulated mRNA expression of the antimicrobial peptides, TAP (∼4.8-fold), BNBD5 (∼3.2-fold) and BNBD10 (∼2.6-fold). Notably, NaB-treated and S. aureus-challenged bMECs increased the mRNA expression of all of the antimicrobial peptides that were evaluated, and this was evident for LAP and BNBD5. In the NaB-treated bMECs, we did not detect significant expression changes for IL-1β and IL-6 and only TNF-α, IL-10 and IL-8 were induced. Interestingly, the NaB-treated and S. aureus-challenged bMECs maintained the anti-inflammatory response that was induced by this SCFA. In conclusion, our results suggest that 0.5mM NaB activates bMECs via TLR2/p38, which leads to improved antimicrobial defense before/after pathogen invasion, and NaB may exert anti-inflammatory effects during infection.

Role of lipid microdomains in TLR-mediated signalling

Over the last twenty years, evidence has been provided that the plasma membrane is partitioned with microdomains, laterally mobile in the bilayer, providing the necessary microenvironment to specific membrane proteins for signalling pathways to be initiated. We discuss here the importance of such microdomains for Toll-like receptors (TLR) localization and function. First, lipid microdomains favour recruitment and clustering of the TLR machinery partners, i.e. receptors and co-receptors previously identified to be required for ligand recognition and signal transmission. Further, the presence of the so-called Cholesterol Recognition Amino-Acid Consensus (CRAC) sequences in the intracellular juxtamembrane domain of several Toll-like receptors suggests a direct role of cholesterol in the activation process. This article is part of a Special Issue entitled: Lipid-protein interactions.

Cutaneous innate immune sensing of Toll-like receptor 2-6 ligands suppresses T cell immunity by inducing myeloid-derived suppressor cells

Skin is constantly exposed to bacteria and antigens, and cutaneous innate immune sensing orchestrates adaptive immune responses. In its absence, skin pathogens can expand, entering deeper tissues and leading to life-threatening infectious diseases. To characterize skin-driven immunity better, we applied living bacteria, defined lipopeptides, and antigens cutaneously. We found suppression of immune responses due to cutaneous infection with Gram-positive S. aureus, which was based on bacterial lipopeptides. Skin exposure to Toll-like receptor (TLR)2-6-binding lipopeptides, but not TLR2-1-binding lipopeptides, potently suppressed immune responses through induction of Gr1(+)CD11b(+) myeloid-derived suppressor cells (MDSCs). Investigating human atopic dermatitis, in which Gram-positive bacteria accumulate, we detected high MDSC amounts in blood and skin. TLR2 activation in skin resident cells triggered interleukin-6 (IL-6), which induced suppressive MDSCs, which are then recruited to the skin suppressing T cell-mediated recall responses such as dermatitis. Thus, cutaneous bacteria can negatively regulate skin-driven immune responses by inducing MDSCs via TLR2-6 activation.

Outcome of Mycobacterium tuberculosis and Toll-like receptor interaction: immune response or immune evasion?

Mycobacterium tuberculosis (M. tuberculosis), the causative agent of tuberculosis, is an intracellular bacterium capable of surviving and persisting within host mononuclear cells. The host response against tubercle bacilli is dominated by fine-tuned interaction of innate and adaptive immune responses. Toll-like receptors (TLRs) play a critical role in the formation of this immune response by facilitating in elaboration of protective T helper type 1 (Th1) cytokines and microbicidal molecules, but the intracellular persistence of M. tuberculosis in the phagosome and processing and presentation of TLR ligands by host antigen-presenting cell leads to continuous and chronic TLR2 signaling. The prolonged stimulation of TLR ultimately results in elaboration of immunosuppressive cytokines and downregulation of antigen presentation by major histocompatibility complex (MHC) class II and therefore becomes beneficial for M. tuberculosis, resulting in its continued survival inside macrophages. An understanding of the host-pathogen interaction in tuberculosis is important to delineate the mechanisms that can modulate the immune response toward protection. This review focuses on the role of TLRs in immune response and immune evasion and how M. tuberculosis maintains its dominance over the host during infection. A precise understanding of the TLRs and M. tuberculosis interaction will undoubtedly lead to the development of novel therapies to combat tuberculosis.

Mycobacterium avium infection induces H-ferritin expression in mouse primary macrophages by activating Toll-like receptor 2

Important for both host and pathogen survivals, iron is a key factor in determining the outcome of an infectious process. Iron with-holding, including sequestration inside tissue macrophages, is considered an important strategy to fight infection. However, for intra-macrophagic pathogens, such as Mycobacterium avium, host defence may depend on intracellular iron sequestration mechanisms. Ferritin, the major intracellular iron storage protein, plays a critical role in this process. In the current study, we studied ferritin expression in mouse bone marrow-derived macrophages upon infection with M. avium. We found that H-ferritin is selectively increased in infected macrophages, through an up-regulation of gene transcription. This increase was mediated by the engagement of Toll like receptor-2, and was independent of TNF-alpha or nitric oxide production. The formation of H-rich ferritin proteins and the consequent iron sequestration may be an important part of the panoply of antimicrobial mechanisms of macrophages.

Contribution of toll-like receptor 2 to the innate response against Staphylococcus aureus infection in mice

Staphylococcus aureus is a common pathogen that causes a wide range of infectious diseases. The function of TLRs, specifically TLR2, during S. aureus infection is still debated. In this study, we investigated the extent to which TLR2 contributes to the host innate response against the bacterial infection using TLR2-deficient mice. Intravenous inoculation with S. aureus resulted in all TLR2-deficient mice dying within 4 d, along with a high bacterial burden in the livers. However, histological examination showed the same degree of macrophage and neutrophil accumulation in the livers of infected TLR2-deficient mice as that in infected wild-type (WT) mice. TLR2-deficient mouse macrophages also showed normal phagocytic activity, although they failed to express CD36 that appeared on the surface of WT mouse cells upon challenge with heat-killed S. aureus. These data indicate that TLR2, as well as CD36, does not directly affect S. aureus clearance and that CD36 expression on macrophages depends on the presence of TLR2. In vivo infection with S. aureus caused significantly elevated production of TNF-α and IL-6 in the livers and blood of TLR2-deficient mice compared with those in WT mice, while the hepatic and serum levels of IL-10 decreased in these mice. In contrast, lower expression of IL-6 and IL-10, but not of TNF-α, at both the gene and protein levels was found in TLR2-deficient mouse macrophages compared to that in WT mouse cells, in response to challenge with heat-killed S. aureus. These findings suggest that the S. aureus-induced pro-inflammatory cytokine response is not dependent on macrophages and that TLR2 deficiency results in decreased IL-10 release by macrophages, which contributes to dysregulated cytokine balance, impaired bacterial clearance, and mouse death. Therefore, TLR2 possesses a protective function during S. aureus infection by regulating pro- and anti-inflammatory cytokine responses.

Involvement of Toll-like receptor 2 in apoptosis of Aggregatibacter actinomycetemcomitans-infected THP-1 cells

BACKGROUND/PURPOSE

Aggregatibacter (Actinobacillus) actinomycetemcomitans is a gram-negative bacterium that has been associated with aggressive periodontitis. A actinomycetemcomitans infection induces apoptosis in the human monocytic cell line THP-1, and p38 mitogen-activated protein kinase (p38) activity and tumor necrosis factor-α (TNF-α) production are enhanced by A actinomycetemcomitans infection. However, mechanisms governing the recognition of A actinomycetemcomitans by monocytes during apoptosis have not been elucidated. A actinomycetemcomitans cell wall components stimulate Toll-like receptor (TLR)2 and/or TLR4. The authors examined whether TLR2 and/or TLR4 were involved in the apoptosis of A actinomycetemcomitans-infected THP-1 cells.

METHODS

A actinomycetemcomitans-infected THP-1 cells were transferred to six-well culture plates and incubated for 0 to 6 hours. In some experiments, THP-1 cells were incubated with anti-TLR2, anti-TLR4, or isotype control antibody (10 μg/mL) for 30 minutes prior to A actinomycetemcomitans infection. Expression of messenger RNA (mRNA) was examined by reverse transcription-polymerase chain reaction. Intracellular bacteria recovered from A actinomycetemcomitans-infected cells and apoptotic cells were detected by APOPercentage dye (Biocolor Ltd, Northern Ireland, UK) staining. Cellular p38 activity and TNF-α production were assessed with enzyme-linked immunosorbent assay.

RESULTS

The expression of TLR2 mRNA was increased by A actinomycetemcomitans infection. Phagocytosis and apoptosis in A actinomycetemcomitans-infected THP-1 cells were inhibited by the addition of anti-TLR2 antibody. Also, anti-TLR2 antibody suppressed the activation of p38 and production of TNF-α in A actinomycetemcomitans-infected THP-1 cells.

CONCLUSION

These results suggest that A actinomycetemcomitans induces increased expression of TLR2, leading to phagocytosis and apoptosis of THP-1 cells via p38 activation and TNF-α production.

Assessment of Lactobacillus gasseri as a candidate oral vaccine vector

Lactobacillus species are commensal bacteria that have long been recognized as probiotic microbes and are generally regarded as safe (GRAS) for human consumption. We have investigated the use of L. gasseri as a vaccine vector for oral immunization against mucosal pathogens. Recent research has shown that the immune response to different lactobacilli can vary widely depending on the species or subspecies of Lactobacillus being studied. While some lactobacilli seem to induce oral tolerance, others induce an adaptive immune response. This study characterized the systemic and mucosal immune response to wild-type and genetically modified L. gasseri. L. gasseri primarily activates TLR2/6, with additional activation through the TLR2 homodimer. To expand the Toll-like receptor (TLR) activation profile of L. gasseri and the immunogenicity of the vector, a plasmid containing fliC, the gene encoding bacterial flagellin, was introduced which resulted in the strong activation of TLR5. The treatment of human myeloid dendritic cells with recombinant lactobacilli expressing flagellin triggered phenotypic maturation and the release of proinflammatory cytokines. In contrast, bacterial treatment also resulted in a statistically significant increase in IL-10 production. In vivo studies established that treatment with L. gasseri led to a diversification of B-cell populations in the lamina propria of the murine colon. Furthermore, treatment with genetically modified L. gasseri led to a significant decrease in the percentage of FoxP3(+) colonic lymphocytes. Taken together, these data clarify the interaction of L. gasseri with the host immune system and support further investigation of the in vivo immunogenicity of L. gasseri expressing both flagellin and candidate vaccine antigens.

Cathelicidin is involved in the intracellular killing of mycobacteria in macrophages

Macrophages have been shown to kill Mycobacterium tuberculosis through the action of the antimicrobial peptide cathelicidin (CAMP), whose expression was shown to be induced by 1,25-dihydroxyvitamin D3 (1,25D3). Here, we investigated in detail the antimycobacterial effect of murine and human cathelicidin against Mycobacterium smegmatis and M. bovis BCG infections. We have synthesized novel LL-37 peptide variants that exhibited potent in vitro bactericidal activity against M. smegmatis, M. bovis BCG and M. tuberculosis H37Rv, as compared with parental peptide. We show that the exogenous addition of LL-37 or endogenous overexpression of cathelicidin in macrophages significantly reduced the intracellular survival of mycobacteria relative to control cells. An upregulation of cathelicidin mRNA expression was observed that correlated with known M. smegmatis killing phases in J774 macrophages. Moreover, RNAi-based Camp knock-down macrophages and Camp(-/-) bone marrow derived mouse macrophages were significantly impaired in their ability to kill mycobacteria. M. smegmatis killing in Camp(-/-) macrophages was less extensive than in Camp(+/+) cells following activation with FSL-1, an inducer of cathelicidin expression. Finally we show that LL-37 and 1,25D3 treatment results in increase in colocalization of BCG-containing phagosomes with lysosomes. Altogether, these data demonstrate that cathelicidin plays an important role in controlling intracellular survival of mycobacteria.

Suppressors of cytokine signaling inhibit effector T cell responses during Mycobacterium tuberculosis infection

Protective immune responses during Mycobacterium tuberculosis (M. tuberculosis) infection are regulated at multiple levels and critically dependent on the balance in the secretion of pro-inflammatory and regulatory cytokines. A key factor that governs this balance at the cellular level is suppressors of cytokine signaling (SOCS). We recently demonstrated that toll-like receptor 2 and dendritic cell (DC)-SIGNR1 differentially regulate SOCS1 expression in DCs during M. tuberculosis infection. This consecutively regulated IL-12 production and determined M. tuberculosis survival. In this study, we characterized the role of SOCS1 in regulating effector responses from CD4(+) and CD8(+) T cells during M. tuberculosis infection. Our data indicate that T cells from M. tuberculosis-infected mice show increased and differential association of SOCS1 with CD3 and CD28, when compared with uninfected mice. While SOCS1 displays increased association with CD3 than CD28 in CD4(+) T cells; SOCS1 is associated more with CD28 than CD3 in CD8(+) T cells. Further, SOCS1 shows increased association with IL-12 and IL-2 receptors in both CD4(+) and CD8(+) T cells from infected mice when compared with naive mice. Silencing SOCS1 in T cells increased signal transduction from T cell receptor (TCR) and CD28 with enhanced activation of key signaling molecules and proliferation. Significantly, SOCS1-silenced T cells mediated enhanced clearance of M. tuberculosis inside macrophages. Finally, adoptive transfer of SOCS1-silenced T cells in M. tuberculosis-infected mice mediated significant reduction in M. tuberculosis loads in spleen. These results exemplify the negative role played by SOCS1 during T cell priming and effector functions during M. tuberculosis infection.

The Toll-like receptor 2 (TLR2) ligand FSL-1 is internalized via the clathrin-dependent endocytic pathway triggered by CD14 and CD36 but not by TLR2

Little is known of how Toll-like receptor (TLR) ligands are processed after recognition by TLRs. This study was therefore designed to investigate how the TLR2 ligand FSL-1 is processed in macrophages after recognition by TLR2. FSL-1 was internalized into the murine macrophage cell line, RAW264.7. Both chlorpromazine and methyl-beta-cyclodextrin, which inhibit clathrin-dependent endocytosis, reduced FSL-1 uptake by RAW264.7 cells in a dose-dependent manner but nystatin, which inhibits caveolae- and lipid raft-dependent endocytosis, did not. FSL-1 was co-localized with clathrin but not with TLR2 in the cytosol of RAW264.7 cells. These results suggest that internalization of FSL-1 is clathrin dependent. In addition, FSL-1 was internalized by peritoneal macrophages from TLR2-deficient mice. FSL-1 was internalized by human embryonic kidney 293 cells transfected with CD14 or CD36 but not by the non-transfected cells. Also, knockdown of CD14 or CD36 in the transfectants reduced FSL-1 uptake. In this study, we suggest that (i) FSL-1 is internalized into macrophages via a clathrin-dependent endocytic pathway, (ii) the FSL-1 uptake by macrophages occurs irrespective of the presence of TLR2, and (iii) CD14 and CD36 are responsible for the internalization of FSL-1.

FSL-1, a bacterial-derived toll-like receptor 2/6 agonist, enhances resistance to experimental HSV-2 infection

Background

Herpes simplex virus type 2 (HSV-2) is a leading cause of genital ulceration that can predispose individuals to an increased risk of acquiring other sexually transmitted infections. There are no approved HSV-2 vaccines and current suppressive therapies require daily compound administration that does not prevent all recurrences. A promising experimental strategy is the use of toll-like receptor (TLR) agonists to induce an innate immune response that provides resistance to HSV-2 infection. Previous studies showed that anti-herpetic activity varied based on origin of the agonists and activation of different TLR indicating that activity likely occurs through elaboration of a specific innate immune response. To test the hypothesis, we evaluated the ability of a bacterial-derived TLR2/6 agonist (FSL-1) to increase resistance to experimental genital HSV-2 infection.

Methods

Vaginal application of FSL-1 at selected doses and times was evaluated to identify potential increased resistance to genital HSV-2 infection in the mouse model. The FSL-1 induced cytokine profile was quantified using kinetically collected vaginal lavages. Additionally, cytokine elaboration and organ weights were evaluated after single or multiple FSL-1 doses to establish a preliminary safety profile. Human vaginal EC cultures were used to confirm the mouse model outcomes.

Results

The results showed that vaginally-applied FSL-1 created an environment resistant to a 25-fold higher HSV-2 challenge dose. Mechanistically, vaginal FSL-1 application led to transient elaboration of cytokines linked to anti-herpetic innate immune responses. No gross local or peripheral immunotoxicity was observed even after multiple dosing. FSL-1 also created an anti-herpetic environment in cultures of human vaginal epithelial cells (EC).

Conclusion

The results showed, for the first time, that the bacterial-derived TLR2/6 agonist FSL-1 induced significant resistance to HSV-2 infection when applied in mice or human vaginal EC cultures. Cytokine evaluation illustrated that anti-herpetic activity correlated with induction of a specific profile. The identified anti-herpetic profile provides an invaluable resource for the future design of novel compounds to reduce genital HSV-2 transmission and improves understanding of the complex innate immune response to potential pathogens elicited by the vaginal mucosa.

CD36 and TLR interactions in inflammation and phagocytosis: implications for malaria

CD36 participates in macrophage internalization of a variety of particles, and has been implicated in inflammatory responses to many of these ligands. To what extent CD36 cooperates with other receptors in mediating these processes remains unclear. Because CD36 has been shown to cooperate with TLR2, we investigated the roles and interactions of CD36 and TLRs in inflammation and phagocytosis. Using Ab-induced endocytosis of CD36 and phagocytosis of erythrocytes displaying Abs to CD36, we show that selective engagement and internalization of this receptor did not lead to proinflammatory cytokine production by primary human and murine macrophages. In addition, CD36-mediated phagocytosis of Plasmodium falciparum malaria-parasitized erythrocytes (PEs), which contain parasite components that activate TLRs, also failed to induce cytokine secretion from primary macrophages. Furthermore, we demonstrate that CD36-mediated internalization did not require TLR2 or the TLR-signaling molecule IRAK4. However, macrophage pretreatment with TLR agonists markedly stimulated particle uptake via CD36. Similarly, PE uptake was unaffected by TLR deficiency, but in wild-type cells was increased by pretreatment with purified P. falciparum glycosylphosphatidylinositols, which activate TLR2. Our findings indicate that CD36 must cooperate with other receptors such as TLRs to participate in cytokine responses. Although purified P. falciparum components activate TLRs, CD36-mediated internalization of intact PEs is not inflammatory. Further, CD36 mediates internalization of particles, including PEs, independently of TLR signaling, but can functionally cooperate with TLRs to enhance internalization.

Toll-like receptor prestimulation increases phagocytosis of Escherichia coli DH5alpha and Escherichia coli K1 strains by murine microglial cells

Meningitis and meningoencephalitis caused by Escherichia coli are associated with high rates of mortality. When an infection occurs, Toll-like receptors (TLRs) expressed by microglial cells can recognize pathogen-associated molecular patterns and activate multiple steps in the inflammatory response that coordinate the brain's local defense, such as phagocytosis of invading pathogens. An upregulation of the phagocytic ability of reactive microglia could improve the host defense in immunocompromised patients against pathogens such as E. coli. Here, murine microglial cultures were stimulated with the TLR agonists Pam(3)CSK(4) (TLR1/TLR2), lipopolysaccharide (TLR4), and CpG oligodeoxynucleotide (TLR9) for 24 h. Upon stimulation, levels of tumor necrosis factor alpha and the neutrophil chemoattractant CXCL1 were increased, indicating microglial activation. Phagocytic activity was studied after adding either E. coli DH5alpha or E. coli K1 strains. After 60 and 90 min of bacterial exposure, the number of ingested bacteria was significantly higher in cells prestimulated with TLR agonists than in unstimulated controls (P < 0.01). Addition of cytochalasin D, an inhibitor of actin polymerization, blocked >90% of phagocytosis. We also analyzed the ability of microglia to kill the ingested E. coli strains. Intracellularly surviving bacteria were quantified at different time points (90, 150, 240, and 360 min) after 90 min of phagocytosis. The number of bacteria killed intracellularly after 6 h was higher in cells primed with the different TLR agonists than in unstimulated microglia. Our data suggest that microglial stimulation by the TLR system can increase bacterial phagocytosis and killing. This approach could improve central nervous system resistance to infections in immunocompromised patients.

Mycobacterium abscessus activates the macrophage innate immune response via a physical and functional interaction between TLR2 and dectin-1

Mycobacterium abscessus (Mab) is an emerging and rapidly growing non-tuberculous mycobacterium (NTM). Compared with M. tuberculosis, which is responsible for tuberculosis, much less is known about NTM-induced innate immune mechanisms. Here we investigated the involvement of pattern-recognition receptors and associated signalling in Mab-mediated innate immune responses. Mab activated the extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinases (MAPKs), and induced the secretion of tumour necrosis factor-alpha, interleukin (IL)-6 and IL-12p40 in murine macrophages via Toll-like receptor (TLR) 2. Notably, the activation of ERK1/2, but not p38, was crucial for Mab-induced pro-inflammatory cytokine production. The ITAM-like motif of dectin-1 critically contributed to Mab internalization and cytokine secretion by macrophages. In addition, dectin-1, in cooperation with TLR2, was required for the efficient phagocytosis of Mab, ERK1/2 activation and pro-inflammatory cytokine secretion. Co-immunoprecipitation and confocal analysis showed the physical interaction and colocalization of dectin-1 with TLR2 following Mab stimulation. Moreover, dectin-1-induced Syk activation was essential for the production of inflammatory cytokines and the release of reactive oxygen species by Mab-infected macrophages. Collectively, these data demonstrate that Mab actively internalizes into and robustly activates innate immune responses in macrophages through a physical and functional interaction between TLR2 and dectin-1.

Resveratrol modulates phagocytosis of bacteria through an NF-kappaB-dependent gene program

Many studies have shown that the pharmacological effects of resveratrol, a phytoalexin polyphenolic compound, include protective effects against cancer and inflammation as well as enhancement of stress resistance. In this study, we examined whether resveratrol affected the phagocytosis of bacteria by macrophages and the activation of the transcription factor NF-kappaB after stimulation with or without the ligand FSL-1 for Toll-like receptor 2 (TLR2). Phagocytosis of Escherichia coli and of Staphylococcus aureus by THP-1 cells and RAW264.7 cells was inhibited by resveratrol in a dose-dependent manner regardless of stimulation with FSL-1. The NF-kappaB activity in HEK293 cells stably expressing TLR2 was also inhibited by resveratrol after stimulation with FSL-1. Resveratrol also inhibited both the translocation of p65 of NF-kappaB into nuclei in the transfectant and tumor necrosis factor alpha production by THP-1 cells or RAW264.7 cells. It has recently been reported that TLR-mediated signaling pathways lead to the upregulation of mRNAs of phagocytic receptors, including scavenger receptors and C-type lectin receptors. This study also demonstrated that FSL-1 induced the upregulation of mRNAs of phagocytic receptors such as macrophage scavenger receptor-1, CD36, DC-SIGN, and Dectin-1 and that the FSL-1-induced upregulation of their mRNAs was inhibited by resveratrol. In addition, it was found that the expression of DC-SIGN in HEK293 cells stably expressing DC-SIGN was reduced by resveratrol and that the phagocytic activity was significantly inhibited by resveratrol. Thus, this study suggests that resveratrol inhibited bacterial phagocytosis by macrophages by downregulating the expression of phagocytic receptors and NF-kappaB activity.

Mycobacterium tuberculosis secretory proteins CFP‐10, ESAT‐6 and the CFP10:ESAT6 complex inhibit lipopolysaccharide‐induced NF‐κB transactivation by downregulation of reactive oxidative species (ROS) production

Mycobacterium tuberculosis (Mtb) causes death of 2-3 million people annually and is considered one of the most successful intracellular pathogens to persist inside the host macrophage. Recent studies have implicated the role of RD-1 region of Mtb genome in the mycobacterial pathogenesis. The role of RD-1-encoded secretory proteins of Mtb in modulation of macrophage function has not been investigated in detail. Here we show that RD-1 encoded two major secretory proteins, namely, culture filtrate protein-10 kDa (CFP-10) and early secreted antigenic target-6 kDa (ESAT-6), and their 1:1 CFP-10:ESAT6 complex inhibit production of reactive oxidative species (ROS) in RAW264.7 cells. These proteins also downregulated the bacterial lipopolysaccharide (LPS)-induced ROS production, which, in turn, downregulated LPS-induced nuclear factor-kappaB (NF-kappaB) p65 DNA-binding activity, as well as inhibited the NF-kappaB-dependent reporter gene (chloramphenicol acetyl transferase) expression in the treated macrophages. Moreover, addition of N-acetyl cysteine, which is a scavenger of ROS, also inhibited LPS-induced reporter gene expression by scavenging the ROS, thereby preventing NF-kappaB transactivation. These studies indicate that the secretory proteins CFP-10, ESAT-6 and the CFP10:ESAT6 complex of Mtb can inhibit LPS-induced NF-kappaB-dependent gene expression via downregulation of ROS production.

A comparison of ovine monocyte-derived macrophage function following infection with Mycobacterium avium ssp. avium and Mycobacterium avium ssp. paratuberculosis

Mycobacterium avium ssp. paratuberculosis causes Johne's disease in ruminants, whereas the antigenically and genetically similar subspecies Mycobacterium avium ssp. avium is less virulent. In this study, we compared one strain of each subspecies for its ability to survive, induce cytokines, suppress MHC class I and II expression and induce apoptosis or necrosis in ovine monocyte-derived macrophages. Both subspecies survived intracellularly and induced the secretion of IL-10. Low levels of TNF-alpha were detected after infection with both subspecies at 4 h. IL-12 was not upregulated after infection. Downregulation of MHC class I and II was evident in response to infection with both M. avium ssp. avium and M. avium ssp. paratuberculosis. No significant cytotoxicity was detectable in ovine macrophages after the addition of bacteria. M. avium ssp. paratuberculosis induced slightly more apoptosis than M. avium ssp. avium. Still the overall rate of apoptosis was very low and both subspecies suppressed LPS-induced macrophage apoptosis.