Mycobacterium paratuberculosis CobT activates dendritic cells via engagement of Toll-like receptor 4 resulting in Th1 cell expansion

Mycobacterium avium subsp. paratuberculosis antigens induce cellular immune responses in cattle without causing reactivity to tuberculin in the tuberculosis skin test

Mycobacterium avium subspecies paratuberculosis (MAP) causes chronic progressive granulomatous enteritis leading to diarrhea, weight-loss, and eventual death in ruminants. Commercially available vaccine provides only partial protection against MAP infection and can interfere with the use of current diagnostic tests for bovine tuberculosis in cattle. Here, we characterized immune responses in calves to vaccines containing four truncated MAP antigens as a fusion (Ag85A^202-347-SOD^1-72-Ag85B^173-330-74F^{1-148+669-786}), either displayed on protein particles, or expressed as a soluble recombinant MAP (rMAP) fusion protein as well as to commercially available Silirum^® vaccine. The rMAP fusion protein elicited the strongest antigen-specific antibody responses to both PPDA and recombinant antigen and strong and long-lasting T-cell immune responses to these antigens, as indicated by increased production of IFN-γ and IL-17A in antigen-stimulated whole blood cultures. The MAP fusion protein particle vaccine induced minimal antibody responses and weak IFN-γ responses but stimulated IL-17A responses to recombinant antigen. The immune response profile of Silirum^® vaccine was characterized by weak antibodies and strong IFN-γ and IL-17A responses to PPDA. Transcription analysis on antigen-stimulated leukocytes from cattle vaccinated with rMAP fusion protein showed differential expression of several immune response genes and genes involved in costimulatory signaling, TLR4, TLR2, PTX3, PTGS2, PD-L1, IL1B, IL2, IL6, IL12B, IL17A, IL22, IFNG, CD40, and CD86. Moreover, the expression of several genes of immune pathways correlated with cellular immune responses in the rMAP fusion protein vaccinated group. These genes have key roles in pathways of mycobacterial immunity, including autophagy, manipulation of macrophage-mediated killing, Th17- and regulatory T cells- (Treg) mediated responses. Calves vaccinated with either the rMAP fusion protein or MAP fusion protein particle vaccine did not induce reactivity to PPDA and PPDB in a comparative cervical skin test, whereas Silirum^® induced reactivity to these tuberculins in most of the vaccinated animals. Overall, our results suggest that a combination of recombinant MAP antigens in the form of a soluble fusion protein vaccine are capable of inducing strong antigen-specific humoral and a balanced Th1/Th17-cell immune response. These findings, together with the absence of reactivity to tuberculin, suggest this subunit vaccine could provide protective immunity against intracellular MAP infection in cattle without compromising the use of current bovine tuberculosis surveillance test.

Protein-Based Adjuvants for Vaccines as Immunomodulators of the Innate and Adaptive Immune Response: Current Knowledge, Challenges, and Future Opportunities

New-generation vaccines, formulated with subunits or nucleic acids, are less immunogenic than classical vaccines formulated with live-attenuated or inactivated pathogens. This difference has led to an intensified search for additional potent vaccine adjuvants that meet safety and efficacy criteria and confer long-term protection. This review provides an overview of protein-based adjuvants (PBAs) obtained from different organisms, including bacteria, mollusks, plants, and humans. Notably, despite structural differences, all PBAs show significant immunostimulatory properties, eliciting B-cell- and T-cell-mediated immune responses to administered antigens, providing advantages over many currently adopted adjuvant approaches. Furthermore, PBAs are natural biocompatible and biodegradable substances that induce minimal reactogenicity and toxicity and interact with innate immune receptors, enhancing their endocytosis and modulating subsequent adaptive immune responses. We propose that PBAs can contribute to the development of vaccines against complex pathogens, including intracellular pathogens such as Mycobacterium tuberculosis, those with complex life cycles such as Plasmodium falciparum, those that induce host immune dysfunction such as HIV, those that target immunocompromised individuals such as fungi, those with a latent disease phase such as Herpes, those that are antigenically variable such as SARS-CoV-2 and those that undergo continuous evolution, to reduce the likelihood of outbreaks.

Screening of Surface-Exposed Lipoproteins of Leptospira Involved in Modulation of Host Innate Immune Response

Leptospira, a zoonotic pathogen, is capable of causing both chronic and acute infection in a susceptible host. Surface-exposed lipoproteins play a major role in modulating the host immune response by activating the innate cells like macrophages and dendritic cells or evading complement attack and killing by phagocytes like neutrophils to favor pathogenesis and establish infection. In this study, we screened some surface-exposed lipoproteins known to be involved in pathogenesis to assess their possible role in immune modulation (innate immune activation or evasion). Surface proteins of the Len family (LenB, LenD, and LenE), Lsa30, Loa22, and Lipl21 were purified in recombinant form and then tested for their ability to activate macrophages of the different host (mouse, human, and bovine). These proteins were tested for binding with complement regulators like Factor H (FH), C4 Binding Protein (C4BP), and host protease Plasminogen (PLG) and also as nucleases to access their possible role in innate immune evasion. Our results show that, of various proteins tested, Loa22 induced strong innate activation and Lsa30 was least stimulatory, as evident from the production of pro-inflammatory cytokines (interleukin-6 and tumor necrosis factor–α) and expression of surface markers [CD80, CD86, and major histocompatibility complex class II (MHCII)]. All the tested proteins were able to bind to FH, C4BP, and PLG; however, Loa22 showed strong binding to PLG correlating to plasmin activity. All the proteins except Loa22 showed nuclease activity, albeit with a requirement of different metal ions. The nuclease activity of these proteins correlated to in vitro degradation of neutrophil extracellular trap (NET). In conclusion, our results indicate that these surface proteins are involved in innate immune modulation and may play a critical role in assisting the bacteria in invading and colonizing the host tissue for persistent infection.

Johne's Disease in Dairy Cattle: An Immunogenetic Perspective

Johne's disease (JD), also known as paratuberculosis, is a severe production-limiting disease with significant economic and welfare implications for the global cattle industry. Caused by infection with Mycobacterium avium subspecies paratuberculosis (MAP), JD manifests as chronic enteritis in infected cattle. In addition to the economic losses and animal welfare issues associated with JD, MAP has attracted public health concerns with potential association with Crohn's disease, a human inflammatory bowel disease. The lack of effective treatment options, such as a vaccine, has hampered JD control resulting in its increasing global prevalence. The disease was first reported in 1895, but in recognition of its growing economic impact, extensive recent research facilitated by a revolution in technological approaches has led to significantly enhanced understanding of the immunological, genetic, and pathogen factors influencing disease pathogenesis. This knowledge has been derived from a variety of diverse models to elucidate host-pathogen interactions including in vivo and in vitro experimental infection models, studies measuring immune parameters in naturally-infected animals, and by studies conducted at the population level to enable the estimation of genetic parameters, and the identification of genetic markers and quantitative trait loci (QTL) putatively associated with susceptibility or resistance to JD. The main objectives of this review are to summarize these recent developments from an immunogenetics perspective and attempt to extract the principal and common findings emerging from this wealth of recent information. Based on these analyses, and in light of emerging technologies such as gene-editing, we conclude by discussing potential future avenues for effectively mitigating JD in cattle.

Corynebacterium diphtheriae Proteome Adaptation to Cell Culture Medium and Serum

Host-pathogen interactions are often studied in vitro using primary or immortal cell lines. This set-up avoids ethical problems of animal testing and has the additional advantage of lower costs. However, the influence of cell culture media on bacterial growth and metabolism is not considered or investigated in most cases. To address this question growth and proteome adaptation of Corynebacterium diphtheriae strain ISS3319 were investigated in this study. Bacteria were cultured in standard growth medium, cell culture medium, and fetal calf serum. Mass spectrometric analyses and label-free protein quantification hint at an increased bacterial pathogenicity when grown in cell culture medium as well as an influence of the growth medium on the cell envelope.

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.

Mycobacterium avium Subspecies paratuberculosis Infects and Replicates within Human Monocyte-Derived Dendritic Cells

BACKGROUND

Mycobacterium avium subspecies paratuberculosis (MAP), a member of the mycobacteriaceae family, causes Johne's disease in ruminants, which resembles Crohn's disease (CD) in humans. MAP was proposed to be one of the causes of human CD, but the evidence remains elusive. Macrophages were reported to be the only cell where MAP proliferates in ruminants and humans and is likely the major producer of TNFα-associated inflammation. However, whether human dendritic cells (DCs), another major antigen-presenting cell (APC), have the ability to harbor MAP and disseminate infection, remains unknown.

METHODS

Human monocyte-derived dendritic cells (moDCs) were infected with MAP and phagocytosis and intracellular survival were quantified by immunofluorescence (IF) and colony counts, respectively. MoDC cytokine expression was measured via ELISA and their activation state was measured via flow cytometry.

RESULTS

We showed that MAP can infect and replicate in human moDCs as means to evade the immune system for successful infection, through inhibition of the phago-lysosome fusion via the secretion of protein tyrosine phosphatase PtpA. This mechanism initially led to a state of tolerance in moDCs and then subsequently caused a pro-inflammatory response as infection persisted, characterized by the upregulation of IL-6 and TNFα, and downregulation of IL-10. Moreover, we showed that moDCs have the ability to phagocytose up to 18% of MAP, when exposed at a multiplicity of infection of 1:1.

CONCLUSION

Infection and subsequent proliferation of MAP within moDCs could provide a unique means for the dissemination of MAP to lymphoid tissue, while altering immune responses to facilitate the persistence of infection of host tissues in CD.

Mycobacterium avium subsp. paratuberculosis MAP1889c Protein Induces Maturation of Dendritic Cells and Drives Th2-biased Immune Responses

Mycobacterium avium subsp. paratuberculosis (MAP) is a causative agent of chronic granulomatous bowel disease in animals and is associated with various autoimmune diseases in humans including Crohn’s disease. A good understanding of the host-protective immune response and antibacterial immunity controlled by MAP and its components may contribute to the development of effective control strategies. MAP1889c was identified as a seroreactive antigen in Crohn’s disease patients. In this study, we investigated the immunological function of MAP1889c in dendritic cells (DCs). MAP1889c stimulated DCs to increase expression of co-stimulatory molecules (CD80 and CD86) and major histocompatibility complex (MHC) class molecules and to secret higher interleukin (IL)-10 and moderate IL-6, tumor necrosis factor (TNF)-α, and IL-12p70 levels through the Toll-like receptor (TLR) 4 pathway. MAP1889c-induced DC activation was mediated by mitogen-activated protein kinases (MAPKs), cAMPp-response element binding protein (CREB), and nuclear factor kappa B (NF-κB). In particular, the CREB signal was essential for MAP1889c-mediated IL-10 production but not TNF-α and IL-12p70. In addition, MAP1889c-matured DCs induced T cell proliferation and drove the Th2 response. Production of lipopolysaccharide (LPS)-mediated pro-inflammatory cytokines and anti-inflammatory cytokines was suppressed and enhanced respectively by MAP1889c pretreatment in DCs and T cells. Furthermore, treatment of MAP1889c in M. avium-infected macrophages promoted intracellular bacterial growth and IL-10 production. These findings suggest that MAP1889c modulates the host antimycobacterial response and may be a potential virulence factor during MAP infection.

Recombinant fusion protein of Heparin-Binding Hemagglutinin Adhesin and Fibronectin Attachment Protein (rHBHA-FAP) of Mycobacterium avium subsp. paratuberculosis elicits a strong gamma interferon response in peripheral blood mononuclear cell culture

Background

Mycobacterium avium subsp. paratuberculosis (MAP) is a causative agent of Johne’s disease in all ruminants worldwide. Economic problems in dairy cattle and sheep industries, public health concern, persistence of MAP in the environment and lack of effective vaccines mentioned necessity of research about various antigens to introduce as vaccine candidates. Based on MAP pathogenesis, it seems that research about the production of new recombinant proteins to stimulate cell-mediated immunity is helpful. This study describes successful expression and purification of a chimeric fusion protein which consists of Heparin-Binding Hemagglutinin Adhesin (HBHA) and high antigenic region of Fibronectin Attachment Protein (FAP-P). Triggered antigen-specific IFN-γ response of isolated PBMCs from immunized goats to rHBHA-FAP and all crude proteins of MAP (PPD), was measured by ELISA.

Results

Significant increases were observed in the IFN-γ production level of peripheral blood mononuclear cells (PBMCs) stimulated by constructed chimeric protein from rHBHA-FAP and PPD vaccinated goats. Antigen-specific gamma interferon (IFN-γ) secretion in positive group (immunized by PPD) against rHBHA-FAP and test group (immunized by rHBHA-FAP) against PPD, also statistically insignificant rises between stimulation with rHBHA-FAP and PPD, suggested the potential and specificity of our chimeric protein to stimulate cell mediated immunity against MAP.

Conclusions

Collectively, these results demonstrate that rHBHA-FAP elicits a strong IFN-γ production in PBMC culture. Therefore, further studies of the present product as a candidate vaccine in naturally infected animals should be conducted, to analyze its potential.

Bacterial Protein Toll-Like-Receptor Agonists: A Novel Perspective on Vaccine Adjuvants

Adjuvants have been used in vaccines for over a century, however, the search for safe and effective vaccine adjuvants continues. In recent decades toll-like-receptor (TLR) agonists have been investigated as potential vaccine adjuvants. In this regard, the majority of the currently investigated TLR agonists are non-protein microbial components such as lipopolysaccharides, oligonucleotides, and lipopeptides. On the other hand, a growing number of studies reveal that TLR signaling and immune responses can be activated by numerous bacterial proteins. However, their potential roles as adjuvants have been somewhat overlooked. Herein, we discuss several such bacterial proteins which exhibit adjuvant properties, including the activation of TLR signaling, antigen presenting cell maturation, pro-inflammatory cytokine production and adaptive immune response. The protein nature of these TLR agonists presents several unique features not shared by non-protein TLR agonists. These properties include the amenability for modifying the structure and function as necessary for optimal immunogenicity and minimal toxicity. Protein adjuvants can be genetically fused to protein antigens which ensure the co-delivery of adjuvant-antigen not only into the same cell but also in the same endocytic cargo, leading to more effective activation of innate and adaptive immune response.

Toll-Like Receptor 4 as an Immune Receptor Against Mycobacterium tuberculosis: A Systematic Review

OBJECTIVE

To review the main Mycobacterium tuberculosis (Mtb) pathogen-associated molecular patterns (PAMPs) and the roles played by toll-like receptor (TLR)4 in determination of Mtb infection outcome.

METHODS

Several scientific databases, including Scopus, PubMed, and Google Scholar, were used for searching appropriate research articles from the literature for information on our topic.

RESULTS

TLR4 plays positive roles in induction of immune responses against Mtb and participates in eradication of the infection. Some limited investigations approved the roles of TLR4 in induction of apoptosis in macrophages during tuberculosis (TB) and attenuation of immune responses in some situations.

CONCLUSIONS

TB outcome appears to be dependent on TLR4/Mtb interaction and several factors, including bacterial load and immune or nonimmune cells, as hosts. Also, other TLR/Mtb interactions can affect TLR4 responses.

MAP1981c, a Putative Nucleic Acid-Binding Protein, Produced by Mycobacterium avium subsp. paratuberculosis, Induces Maturation of Dendritic Cells and Th1-Polarization

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative pathogen of chronic granulomatous enteropathy (Johne's disease) in animals, and has been focused on its association with various autoimmune diseases in humans, including Crohn's disease. The discovery of novel mycobacterial antigens and exploring their role in host immunity can contribute to the advancement of effective defense strategies including vaccines and diagnostic tools. In a preliminary study, we identified cellular extract proteins of MAP that strongly react with the blood of patients with Crohn's disease. In particular, MAP1981c, a putative nucleic acid-binding protein, showed high expression levels and strong reactivity to IgG and IgM in the sera of patients. Here, we investigated the immunological features of MAP1981c and focused on its interaction with dendritic cells (DCs), confirming its immunomodulatory ability. MAP1981c was shown to recognize Toll-like receptor (TLR) 4, and induce DC maturation and activation by increasing the expression of co-stimulatory (CD80 and CD86) and MHC class I/II molecules and the secretion of pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α) in DCs. This DC activation by MAP1981c was mediated by downstream signaling of TLR4 via MyD88- and TRIF-, MAP kinase-, and NF-κB-dependent signaling pathways. In addition, MAP1981c-treated DCs activated naïve T cells and induced the differentiation of CD4⁺ and CD8⁺ T cells to express T-bet, IFN-γ, and/or IL-2, but not GATA-3 and IL-4, thus indicating that MAP1981c contributes to Th1-type immune responses both in vitro and in vivo. Taken together, these results suggest that MAP1981c is a novel immunocompetent antigen that induces DC maturation and a Th1-biased response upon DC activation, suggesting that MAP1981c can be an effective vaccine and diagnostic target.

A novel Th1-type T-cell immunity-biasing effect of malate dehydrogenase derived from Mycobacterium avium subspecies paratuberculosis via the activation of dendritic cells

Mycobacterium avium subspecies paratuberculosis (MAP) is the causative pathogen of Johne's disease in ruminants, characterized by chronic granulomatous enteritis; it also has zoonotic potential and is associated with Crohn's disease in humans. A better understanding of the mycobacterial antigens and their roles in the host immune response may facilitate the rational design of control strategies, including the development of effective vaccines and diagnostic tools. However, the functional roles of a large proportion of MAP antigens involved in modulating the host immune response remain unknown. In this study, an immunological role of MAP malate dehydrogenase (MDH, MAP2541c), an antigen that is upregulated in stress culture conditions, such as nutrient starvation and hypoxia, in polarizing naïve CD4⁺/CD8⁺ T cells toward Th1-biased T-cell immunity via the activation of dendritic cells (DCs) was identified. DCs treated with MAP MDH displayed characteristics of the activated and mature immune status, with augmented expression of cell surface molecules and pro-inflammatory cytokines, including TNF-α, IL-1β, IL-6, and IL-12p70, but not IL-10, along with a dose-dependent decrease in the antigen uptake capacity. A mechanistic investigation revealed that the observed DC maturation is mediated by the activation of JNK, ERK, and p38 MAP kinases, and the NF-κB signaling pathway. Notably, DCs activated by MAP MDH treatment promoted naïve CD4⁺/CD8⁺ T cell proliferation; in particular, they effectively polarized naïve CD4⁺ T cells to secrete IFN-γ and IL-2 and activate T-bet, but, unlike the LPS control, did not influence IL-5 and GATA-3. These results indicated that MAP MDH has the potential to induce the Th1 cell response via DC activation. Collectively, our data demonstrated that MAP MDH is a novel immunostimulatory antigen that drives Th1-biased T cell polarization via interactions with DCs, suggesting that MDP MDH has the potential to be an effective MAP vaccine antigen target and diagnostic marker.

Mycobacterium leprae Activates Toll-Like Receptor-4 Signaling and Expression on Macrophages Depending on Previous Bacillus Calmette-Guerin Vaccination

Toll-like receptor (TLR)-1 and TLR2 have been shown to be receptors for Mycobacterium leprae (M. leprae), yet it is unclear whether M. leprae can signal through alternative TLRs. Other mycobacterial species possess ligands for TLR4 and genetic association studies in human populations suggest that people with TLR4 polymorphisms may be protected against leprosy. Using human embryonic kidney (HEK)-293 cells co-transfected with TLR4, we demonstrate that M. leprae activates TLR4. We used human macrophages to show that M. leprae stimulation of cytokine production is diminished if pre-treated with TLR4 neutralizing antibody. TLR4 protein expression was up-regulated on macrophages derived from non-bacillus Calmette-Guerin (BCG) vaccinated healthy volunteers after incubation with M. leprae, whereas it was down-regulated in macrophages derived from BCG-vaccinated donors. Finally, pre-treatment of macrophages derived from BCG-naive donors with BCG reversed the effect of M. leprae on TLR4 expression. This may be a newly described phenomenon by which BCG vaccination stimulates “non-specific” protection to the human immune system.

Streptococcus pneumoniae Endopeptidase O (PepO) Elicits a Strong Innate Immune Response in Mice via TLR2 and TLR4 Signaling Pathways

Interaction between virulence factors of Streptococcus pneumoniae and innate immune receptors elicits host responses through specific signaling pathways during infection. Insights into the signaling events may provide a better knowledge of the starting events for host-pathogen interaction. Here we demonstrated a significant induction of innate immune response elicited by recombinant S. pneumoniae endopeptidase O (rPepO), a newer pneumococcal virulence protein, both in vivo and in vitro. Intratracheal instillation of rPepO protein resulted in significant increase of cytokines production and neutrophils infiltration in mouse lungs. TLR2 or TLR4 deficient mice subjected to rPepO treatment showed decreased cytokines production, reduced neutrophils infiltration and intensified tissue injury as compared with WT mice. Upon stimulation, cytokines TNF-α, IL-6, CXCL1, and CXCL10 were produced by peritoneal exudate macrophages (PEMs) in a TLR2 and TLR4 dependent manner. rPepO-induced cytokines production was markedly decreased in TLR2 or TLR4 deficient PEMs. Further study revealed that cytokines induction relied on the rapid phosphorylation of p38, Akt and p65, not the activation of ERK or JNK. While in TLR2 or TLR4 deficient PEMs the activation of p65 was undetectable. Taken together, these results indicate for the first time that the newer pneumococcal virulence protein PepO activates host innate immune response partially through TLR2 and TLR4 signaling pathways.

House dust mite allergens mediate the activation of c‑kit in dendritic cells via Toll‑like receptor 2

Several studies have demonstrated that the c‑kit proto‑oncogene and its ligand, stem cell factor, are important in the development of asthma. House dust mite (HDM; Dermatophagoides pteronyssinus) allergens are a major trigger in the development and exacerbation of asthma. HDM allergens can induce the activation of c‑kit in dendritic cells (DCs), leading to the development of allergic asthma. Previous studies have demonstrated that activation of Toll‑like receptor 2 (TLR2) evokes a T helper (Th)2 immune response and promotes experimental asthma. The aim of the present study was to assess whether HDM mediates the activation of c‑kit in DCs via TLR2. Monocyte‑derived DCs were generated from C57BL/6 mice, and cultured with interleukin (IL)‑4 and granulocyte‑macrophage colony‑stimulating factor. The DCs were then sensitized with HDM (10 µg/ml) for 72 h. TLR2‑specific small interfering (si)RNA was used to silence and inhibit the expression of TLR2 in the DCs. The expression levels of c‑kit and B7 (CD80/CD86) were measured, by analyzing the DC culture supernatant for the presence of IL‑6 and IL‑12. Inhibition of TLR2 using specific siRNA downregulated the expression of c‑kit in the HDM‑activated DCs. In addition, silencing of TLR2 inhibited the expression of CD80/CD86, decreased the production of IL‑6, and increased the production of IL‑12. These results indicated that TRL2 are important in the activation of c‑kit by HDM in DCs.

Mycobacterium abscessus MAB2560 induces maturation of dendritic cells via Toll-like receptor 4 and drives Th1 immune response

In this study, we showed that Mycobacterium abscessus MAB2560 induces the maturation of dendritic cells (DCs), which are representative antigen-presenting cells (APCs). M. abscessus MAB2560 stimulate the production of pro-inflammatory cytokines [interleukin (IL)-6, tumor necrosis factor (TNF)-α, IL-1β, and IL-12p70] and reduce the endocytic capacity and maturation of DCs. Using TLR4-/- DCs, we found that MAB2560 mediated DC maturation via Toll-like receptor 4 (TLR4). MAB2560 also activated the MAPK signaling pathway, which was essential for DC maturation. Furthermore, MAB2560- treated DCs induced the transformation of naïve T cells to polarized CD4+ and CD8+ T cells, which would be crucial for Th1 polarization of the immune response. Taken together, our results indicate that MAB2560 could potentially regulate the host immune response to M. abscessus and may have critical implications for the manipulation of DC functions for developing DC-based immunotherapy.

Essential engagement of Toll-like receptor 2 in initiation of early protective Th1 response against rough variants of Mycobacterium abscessus

Although Mycobacterium abscessus (M. abscessus) is becoming more prevalent in patients without overt immunodeficiency, little is known about the factors that contribute to disease susceptibility. This study was undertaken to investigate how Toll-like receptor 2 (TLR2) functionally contributes to the generation of protective immunity against M. abscessus in a morphotype-specific manner. We found that Tlr2-/- mice were extremely susceptible to an intravenous (i.v.) model of infection by M. abscessus rough variants, displaying uncontrolled infection in the lungs and a significantly lower survival rate than with wild-type (WT) mice. This uncontrolled infection resulted from failures in the following processes: (i) production of the crucial cytokines gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin 12p70 (IL-12p70); (ii) early infiltration of neutrophils, monocytes, and dendritic cells (DCs) in the lungs of Tlr2-/- mice; (iii) rapid influx of CD4+ and CD8+ T cells; and (iv) the expansion of memory/effector T cells. Notably, systemic administration of M. abscessus culture filtrate-treated syngeneic DCs from WT mice greatly strengthened immune priming in vivo, resulting in a dramatic reduction in bacterial growth and improved long-term survival in Tlr2-/- mice, with a recovery of protective immunity. Our findings demonstrate that TLR2 is an essential contributor to instructive and effector immunity during M. abscessus infection in a morphotype-specific manner.

Mucosal and systemic immunization with a novel attenuated pneumococcal vaccine candidate confer serotype independent protection against Streptococcus pneumoniae in mice

Despite the availability of effective vaccines, Streptococcus pneumoniae is still one of the major infectious diseases causing substantial morbidity and mortality in children under 5 years old. In this study, we demonstrate the protective efficacy of S. pneumoniae SPY1, a novel live attenuated vaccine strain against pneumococcal infection in murine models. This strain was characterized by defects in three important pneumococcal virulence factors including capsule, teichoic acids and pneumolysin. The lactate dehydrogenase assays and in vivo animal experiments demonstrated a significantly attenuated virulence and a reduced nasopharyngeal colonization for the SPY1 strain. We also show that mucosal and systemic immunization with the live SPY1 strain induced protective immune responses against pneumococci. Mucosal immunization with SPY1 offered better protection against colonization challenge with strains TIGR4 and serotype 19F than systemic SPY1 immunization. In invasive infection models, mucosal vaccination with the SPY1 strain conferred complete protection against D39 and clinical serotype 6B and 3 strains. Notably, intranasal vaccination with the SPY1 strain conferred superior protection against pneumococcal invasive disease compared with the commercial available vaccines. SPY1 strain was shown to elicit high levels of serotype-independent antibodies and a mixed cellular immune response. Besides, the SPY1 serum was able to passively protect mice against invasive challenge with D39 strain, indicating the protective effect of the antibody-mediated responses. Together, the SPY1 strain may be a promising live vaccine strain to protect pneumococcal infection.

Impact of host genetics on susceptibility and resistance to Mycobacterium avium subspecies Paratuberculosis infection in domestic ruminants

Johne's disease or Paratuberculosis has emerged as major infectious disease of animals in general and domestic livestock in particular on global basis. There have been major initiatives in developed countries for the control of this incurable malady of animals and human beings alike (inflammatory bowel disease or Crohn's disease). Disease has not received similar attention due to inherent complexities of disease, diagnosis and control, in resource poor counties around the world. However, the rich genetic diverstiy of the otherwise low productive animal population offers opportunity for the control of Johne's disease and improve per animal productivity. Present review aims to gather and compile information available on genetics or resistance to Johne's disease and its future exploitation by resource poor countries rich in animal diversity. This review will also help to create awareness and share knowledge and experience on prevalence and opportunities for control of Johne's disease in the livestock population to boost per animal productivity among developing and poor countries of the world. Breeding of animals for disease resistance provides good, safe, effective and cheaper way of controlling Johne's disease in animals, with especial reference to domestic livestock of developing and poor countries. Study will help to establish better understanding of the correlation between host cell factors and resistance to MAP infection which may have ultimately help in the control of Johne's disease in future.

No holes barred: invasion of the intestinal mucosa by Mycobacterium avium subsp. paratuberculosis

The infection biology of Mycobacterium avium subsp. paratuberculosis has recently crystallized, with added details surrounding intestinal invasion. The involvement of pathogen-derived effector proteins such as the major membrane protein, oxidoreductase, and fibronectin attachment proteins have been uncovered. Mutations constructed in this pathogen have also shed light on genes needed for invasion. The host cell types that are susceptible to invasion have been defined, along with their transcriptional response. Recent details have given a new appreciation for the dynamic interplay between the host and bacterium that occurs at the outset of infection. An initial look at the global expression pathways of the host has shown a circumvention of the cell communication pathway by M. avium subsp. paratuberculosis, which loosens the integrity of the tight junctions. We now know that M. avium subsp. paratuberculosis activates the epithelial layer and also actively recruits macrophages to the site of infection. These notable findings are summarized along with added mechanistic details of the early infection model. We conclude by proposing critical next steps to further elucidate the process of M. avium subsp. paratuberculosis invasion.