CpG oligodeoxynucleotides stimulate protective innate immunity against pulmonary Klebsiella infection

Trained immunity-inducing vaccines: Harnessing innate memory for vaccine design and delivery

While the efficacy of many current vaccines is well-established, various factors can diminish their effectiveness, particularly in vulnerable groups. Amidst emerging pandemic threats, enhancing vaccine responses is critical. Our review synthesizes insights from immunology and epidemiology, focusing on the concept of trained immunity (TRIM) and the non-specific effects (NSEs) of vaccines that confer heterologous protection. We elucidate the mechanisms driving TRIM, emphasizing its regulation through metabolic and epigenetic reprogramming in innate immune cells. Notably, we explore the extended protective scope of vaccines like BCG and COVID-19 vaccines against unrelated infections, underscoring their role in reducing neonatal mortality and combating diseases like malaria and yellow fever. We also highlight novel strategies to boost vaccine efficacy, incorporating TRIM inducers into vaccine formulations to enhance both specific and non-specific immune responses. This approach promises significant advancements in vaccine development, aiming to improve global public health outcomes, especially for the elderly and immunocompromised populations.

Klebsiella pneumoniae vaccine studies in animal models

The treatment of Klebsiella pneumoniae is faced with challenges demanding the development of a vaccination strategy. However, no approved and globally available vaccine exists yet. This study aimed to systematically review all published data on K. pneumoniae vaccines in animal models. Without time restrictions, electronic databases were searched using appropriate keywords. The retrieved studies were screened and the data of those that matched our inclusion criteria were collected and analyzed. In total, 2027 records were retrieved; of which 35 studies were included for systematic review. The most frequently used animal model was BALB/c mice. Proteins, polysaccharides, and their combinations (conjugates) were the most common vaccine candidates used. The amount of antigen, the route used for immunization, and the challenge strategy was varying in the studies and were chosen based on several factors such as the animal model, the type of antigen, and the schedule of immunization. Almost all studies claimed that their vaccine was effective/protective, indicated by increasing survival rate, reducing organ bacterial load, and eliciting protective antibody and/or cytokine responses. Altogether, the information presented here will assist researchers to have a better look at the K. pneumoniae vaccine candidates and to take more effective steps in the future.

Host Immune Response to Clinical Hypervirulent Klebsiella pneumoniae Pulmonary Infections via Transcriptome Analysis

Klebsiella pneumoniae (K. pneumoniae), especially those with hypervirulence, is becoming a global concern and posing great threat to human health. Studies on individual immune cells or cytokines have partially revealed the function of the host immune defense against K. pneumoniae pulmonary infection. However, systematic immune response against K. pneumoniae has not been fully elucidated. Herein, we report a transcriptome analysis of the lungs from a mouse pneumonia model infected with a newly isolated K. pneumoniae clinical strain YBQ. Total RNA was isolated from the lungs of mice 48 hours post infection to assess transcriptional alteration of genes. Transcriptome data were analyzed with KEGG, GO, and ICEPOP. Results indicated that upregulated transcription level of numerous cytokines and chemokines was coordinated with remarkably activated ribosome and several critical immune signaling pathways, including IL-17 and TNF signaling pathways. Notably, transcription of cysteine cathepsin inhibitor (stfa1, stfa2, and stfa3) and potential cysteine-type endopeptidase inhibitor (cstdc4, cstdc5, and cstdc6) were upregulated. Results of ICEPOP showed neutrophils functions as the most essential cell type against K. pneumoniae infection. Critical gene alterations were further validated by rt-PCR. Our findings provided a global transcriptional perspective on the mechanisms of host defense against K. pneumoniae infection and revealed some unique responding genes.

Placental mesenchymal stem cells boost M2 alveolar over M1 bone marrow macrophages via IL-1β in Klebsiella-mediated acute respiratory distress syndrome

RATIONALE

Acute respiratory distress syndrome (ARDS) is a lethal complication of severe bacterial pneumonia due to the inability to dampen overexuberant immune responses without compromising pathogen clearance. Both of these processes involve tissue-resident and bone marrow (BM)-recruited macrophage (MΦ) populations which can be polarised to have divergent functions. Surprisingly, despite the known immunomodulatory properties of mesenchymal stem cells (MSCs), simultaneous interactions with tissue-resident and recruited BMMΦ populations are largely unexplored.

OBJECTIVES

We assessed the therapeutic use of human placental MSCs (PMSCs) in severe bacterial pneumonia with elucidation of the roles of resident alveolar MΦs (AMΦs) and BMMΦs.

METHODS

We developed a lethal, murine pneumonia model using intratracheal infection of a clinically relevant Klebsiella pneumoniae (KP) strain with subsequent intravenous human PMSC treatment. Pulmonary AMΦ and recruited BMMΦ analyses, histological evaluation, bacterial clearance and mice survival were assessed. To elucidate the role of resident AMΦs in improving outcome, we performed AMΦ depletion in the KP-pneumonia model with intratracheal clodronate pretreatment.

MEASUREMENTS AND MAIN RESULTS

Human PMSC treatment decreased tissue injury and improved survival of severe KP-pneumonia mice by decreasing the presence and function of recruited M1 BMMΦ while preserving M2 AMΦs and enhancing their antibacterial functions. Interestingly, PMSC therapy failed to rescue AMΦ-depleted mice with KP pneumonia, and PMSC-secreted IL-1β was identified as critical in increasing AMΦ antibacterial activities to significantly improve pathogen clearance-especially bacteraemia-and survival.

CONCLUSIONS

Human PMSC treatment preferentially rescued resident M2 AMΦs over recruited M1 BMMΦs with overall M2 polarisation to improve KP-related ARDS survival.

TLR Agonists as Mediators of Trained Immunity: Mechanistic Insight and Immunotherapeutic Potential to Combat Infection

Despite advances in critical care medicine, infection remains a significant problem that continues to be complicated with the challenge of antibiotic resistance. Immunocompromised patients are highly susceptible to development of severe infection which often progresses to the life-threatening condition of sepsis. Thus, immunotherapies aimed at boosting host immune defenses are highly attractive strategies to ward off infection and protect patients. Recently there has been mounting evidence that activation of the innate immune system can confer long-term functional reprogramming whereby innate leukocytes mount more robust responses upon secondary exposure to a pathogen for more efficient clearance and host protection, termed trained immunity. Toll-like receptor (TLR) agonists are a class of agents which have been shown to trigger the phenomenon of trained immunity through metabolic reprogramming and epigenetic modifications which drive profound augmentation of antimicrobial functions. Immunomodulatory TLR agonists are also highly beneficial as vaccine adjuvants. This review provides an overview on TLR signaling and our current understanding of TLR agonists which show promise as immunotherapeutic agents for combating infection. A brief discussion on our current understanding of underlying mechanisms is also provided. Although an evolving field, TLR agonists hold strong therapeutic potential as immunomodulators and merit further investigation for clinical translation.

A novel gonorrhea vaccine composed of MetQ lipoprotein formulated with CpG shortens experimental murine infection

Bacterial surface lipoproteins are emerging as attractive vaccine candidates due to their biological importance and the feasibility of their large-scale production for vaccine manufacturing. The global prevalence of gonorrhea, resistance to antibiotics, and serious consequences to reproductive and neonatal health necessitate development of effective vaccines. Reverse vaccinology identified the surface-displayed L-methionine binding lipoprotein MetQ (NGO2139) and its homolog GNA1946 (NMB1946) as gonococcal and meningococcal vaccine candidates, respectively. Here, we assessed the suitability of MetQ for inclusion in a gonorrhea vaccine by examining MetQ conservation, its function inNeisseria gonorrhoeae (Ng) pathogenesis, and its ability to induce protective immune responses using a female murine model of lower genital tract infection. In-depth bioinformatics, phylogenetics and mapping the most prevalent Ng polymorphic amino acids to the GNA1946 crystal structure revealed remarkable MetQ conservation: ~97% Ng isolates worldwide possess a single MetQ variant. Mice immunized with rMetQ-CpG (n = 40), a vaccine containing a tag-free version of MetQ formulated with CpG, exhibited robust, antigen-specific antibody responses in serum and at the vaginal mucosae including IgA. Consistent with the activity of CpG as a Th1-stimulating adjuvant, the serum IgG1/IgG2a ratio of 0.38 suggested a Th1 bias. Combined data from two independent challenge experiments demonstrated that rMetQ-CpG immunized mice cleared infection faster than control animals (vehicle, p < 0.0001; CpG, p = 0.002) and had lower Ng burden (vehicle, p = 0.03; CpG, p < 0.0001). We conclude rMetQ-CpG induces a protective immune response that accelerates bacterial clearance from the murine lower genital tract and represents an attractive component of a gonorrhea subunit vaccine.

The Central Role and Possible Mechanisms of Bacterial DNAs in Sepsis Development

The pathological roles of bacterial DNA have been documented many decades ago. Bacterial DNAs are different from mammalian DNAs; the latter are heavily methylated. Mammalian cells have sensors such as TLR-9 to sense the DNAs with nonmethylated CpGs and distinguish them from host DNAs with methylated CpGs. Further investigation has identified many other types of DNA sensors distributed in a variety of cellular compartments. These sensors not only sense foreign DNAs, including bacterial and viral DNAs, but also sense damaged DNAs from the host cells. The major downstream signalling pathways includeTLR-9-MyD88-IKKa-IRF-7/NF-κB pathways to increase IFN/proinflammatory cytokine production, STING-TBK1-IRF3 pathway to increase IFN-beta, and AIM2-ASC-caspas-1 pathway to release IL-1beta. The major outcome is to activate host immune response by inducing cytokine production. In this review, we focus on the roles and potential mechanisms of DNA sensors and downstream pathways in sepsis. Although bacterial DNAs play important roles in sepsis development, bacterial DNAs alone are unable to cause severe disease nor lead to death. Priming animals with bacterial DNAs facilitate other pathological factors, such as LPS and other virulent factors, to induce severe disease and lethality. We also discuss compartmental distribution of DNA sensors and pathological significance as well as the transport of extracellular DNAs into cells. Understanding the roles of DNA sensors and signal pathways will pave the way for novel therapeutic strategies in many diseases, particularly in sepsis.

Evaluation of a new live recombinant vaccine against cutaneous leishmaniasis in BALB/c mice

Background

Leishmaniasis is a serious health problem in some parts of the world. In spite of the many known leishmaniasis control measures, the disease has continued to increase in endemic areas, and no effective vaccine has been discovered.

Methods

In this study, Leishmania tarentulae was used as a living factory for the production of two LACK and KMP11 immunogenic antigens in the mice body, and safety profiles were investigated. The sequences of the KMP11 and LACK L. major antigens were synthesized in the pLEXSY-neo 2.1 plasmid and cloned into E. coli strain Top10, and after being linearized with the SwaI enzyme, they were transfected into the genome of L. tarentolae. The L. tarentolae-LACK/KMP11/EGFP in the stationary phase with CpG ODN as an adjuvant was used for vaccination in BALB/c mice. Vaccination was performed into the left footpad. Three weeks later, the booster was injected in the same manner. To examine the effectiveness of the injected vaccine, pathogenic L. major (MRHO/IR/75/ER) was injected into the right footpad of all mice three weeks following the booster vaccination. In order to assess humoral immunity, the levels of IgG1, and IgG2a antibodies before and 6 weeks after the challenge were studied in the groups. In addition, in order to investigate cellular immunity in the groups, the study measured IFN-γ, IL-5, TNF-α, IL-6 and IL-17 cytokines before, 3 weeks and 8 weeks after the challenge, and also the parasite load in the lymph node with real-time PCR.

Results

The lowest level of the parasitic load was observed in the G1 group (mice vaccinated with L. tarentolae-LACK/KMP11/EGFP with CpG) in comparison with other groups (L. tarentolae-LACK/KMP11/EGFP +non-CpG (G2); L. tarentolae-EGFP + CpG (G3, control); L. tarentolae-EGFP + non-CpG (G4, control); and mice injected with PBS (G5, control). Moreover, the evaluation of immune response showed a delayed-type hypersensitivity towards Th1.

Conclusions

According to the results of this study, the live recombinant vaccine of L. tarentolae-LACK/KMP11/EGFP with the CpG adjuvant reduced the parasitic load and footpad induration in infected mice. The long-term effects of this vaccine can be evaluated in volunteers as a clinical trial in future planning.

CpG-DNA induces bacteria-reactive IgM enhancing phagocytic activity against Staphylococcus aureus infection

CpG-DNA triggers the proliferation and differentiation of B cells which results in the increased production of antibodies. The presence of bacteria-reactive IgM in normal serum was reported; however, the relevance of CpG-DNA with the production of bacteria-reactive IgM has not been investigated. Here, we proved the function of CpG-DNA for the production of bacteria-reactive IgM. CpG-DNA administration led to increased production of bacteria-reactive IgM both in the peritoneal fluid and serum through TLR9 signaling pathway. When we stimulated B cells with CpG-DNA, production of bacteria-reactive IgM was reproduced in vitro. We established a bacteria-reactive monoclonal IgM antibody using CpG-DNA stimulated-peritoneal B cells. The monoclonal IgM antibody enhanced the phagocytic activity of RAW 264.7 cells against S. aureus MW2 infection. Therefore, we suggest that CpG-DNA enhances the antibacterial activity of the immune system by triggering the production of bacteria-reactive IgM. We also suggest the possible application of the antibodies for the treatment of antibiotics-resistant bacterial infections.

15-Epi-LXA4 and 17-epi-RvD1 restore TLR9-mediated impaired neutrophil phagocytosis and accelerate resolution of lung inflammation

Timely resolution of bacterial infections critically depends on phagocytosis of invading pathogens by polymorphonuclear neutrophil granulocytes (PMNs), followed by PMN apoptosis and efferocytosis. Here we report that bacterial DNA (CpG DNA) and mitochondrial DNA impair phagocytosis and attenuate phagocytosis-induced apoptosis in human PMNs through Toll-like receptor 9 (TLR9)-mediated release of neutrophil elastase and proteinase 3 and subsequent down-regulation of the complement receptor C5aR. Consistently, CpG DNA delays pulmonary clearance of Escherichia coli in mice and suppresses PMN apoptosis, efferocytosis, and generation of proresolving lipid mediators, thereby prolonging lung inflammation evoked by E. coli Genetic deletion of TLR9 renders mice unresponsive to CpG DNA. We also show that aspirin-triggered 15-epi-lipoxin A₄ (15-epi-LXA₄) and 17-epi-resolvin D1 (17-epi-RvD1) through the receptor ALX/FPR2 antagonize cues from CpG DNA, preserve C5aR expression, restore impaired phagocytosis, and redirect human PMNs to apoptosis. Treatment of mice with 15-epi-LXA₄ or 17-epi-RvD1 at the peak of inflammation accelerates clearance of bacteria, blunts PMN accumulation, and promotes PMN apoptosis and efferocytosis, thereby facilitating resolution of E. coli-evoked lung injury. Collectively, these results uncover a TLR9-mediated endogenous mechanism that impairs PMN phagocytosis and prolongs inflammation, and demonstrate both endogenous and therapeutic potential for 15-epi-LXA₄ and 17-epi-RvD1 to restore impaired bacterial clearance and facilitate resolution of acute lung inflammation.

Anti-Bacterial Effect of CpG-DNA Involves Enhancement of the Complement Systems

CpG-DNA activates the host immune system to resist bacterial infections. In this study, we examined the protective effect of CpG-DNA in mice against Escherichia coli (E. coli) K1 infection. Administration of CpG-DNA increased the survival of mice after E. coli K1 infection, which reduces the numbers of bacteria in the organs. Pre-injection of mice with CpG-DNA before E. coli K1 infection increased the levels of the complement C3 but not C3a and C3b. The survival of the mice after E. coli K1 infection was significantly decreased when the mice were pre-injected with the cobra venom factor (CVF) removing the complement compared to the non-CVF-treated mice group. It suggests that the complement has protective roles against E. coli K1 infection. In addition, the survival of complement-depleted mice was increased by CpG-DNA pre-administration before E. coli K1 infection. Therefore, we suggest that CpG-DNA enhances the anti-bacterial activity of the immune system by augmenting the levels of complement systems after E. coli K1 infection and triggering other factors as well. Further studies are required to investigate the functional roles of the CpG-DNA-induced complement regulation and other factors against urgent bacterial infection.

Klebsiella pneumoniae infection biology: living to counteract host defences

Klebsiella species cause a wide range of diseases including pneumonia, urinary tract infections (UTIs), bloodstream infections and sepsis. These infections are particularly a problem among neonates, elderly and immunocompromised individuals. Klebsiella is also responsible for a significant number of community-acquired infections. A defining feature of these infections is their morbidity and mortality, and the Klebsiella strains associated with them are considered hypervirulent. The increasing isolation of multidrug-resistant strains has significantly narrowed, or in some settings completely removed, the therapeutic options for the treatment of Klebsiella infections. Not surprisingly, this pathogen has then been singled out as an 'urgent threat to human health' by several organisations. This review summarises the tremendous progress that has been made to uncover the sophisticated immune evasion strategies of K. pneumoniae. The co-evolution of Klebsiella in response to the challenge of an activated immune has made Klebsiella a formidable pathogen exploiting stealth strategies and actively suppressing innate immune defences to overcome host responses to survive in the tissues. A better understanding of Klebsiella immune evasion strategies in the context of the host-pathogen interactions is pivotal to develop new therapeutics, which can be based on antagonising the anti-immune strategies of this pathogen.

CpG-DNA exerts antibacterial effects by protecting immune cells and producing bacteria-reactive antibodies

CpG-DNA activates various immune cells, contributing to the host defense against bacteria. Here, we examined the biological function of CpG-DNA in the production of bacteria-reactive antibodies. The administration of CpG-DNA increased survival in mice following infection with methicillin-resistant S. aureus and protected immune cell populations in the peritoneal cavity, bone marrow, and spleen. CpG-DNA injection likewise increased bacteria-reactive antibodies in the mouse peritoneal fluid and serum, which was dependent on TLR9. B cells isolated from the peritoneal cavity produced bacteria-reactive antibodies in vitro following CpG-DNA administration that enhanced the phagocytic activity of the peritoneal cells. The bacteria-reactive monoclonal antibody enhanced phagocytosis in vitro and protected mice after S. aureus infection. Therefore, we suggest that CpG-DNA enhances the antibacterial activity of the immune system by protecting immune cells and triggering the production of bacteria-reactive antibodies. Consequently, we believe that monoclonal antibodies could aid in the treatment of antibiotic-resistant bacterial infections.

Lung epithelial cells: therapeutically inducible effectors of antimicrobial defense

Lung epithelial cells are increasingly recognized to be active effectors of microbial defense, contributing to both innate and adaptive immune function in the lower respiratory tract. As immune sentinels, lung epithelial cells detect diverse pathogens through an ample repertoire of membrane-bound, endosomal, and cytosolic pattern-recognition receptors (PRRs). The highly plastic epithelial barrier responds to detected threats via modulation of paracellular flux, intercellular communications, mucin production, and periciliary fluid composition. Epithelial PRR stimulation also induces production of cytokines that recruit and sculpt leukocyte-mediated responses, and promotes epithelial generation of antimicrobial effector molecules that are directly microbicidal. The epithelium can alternately enhance tolerance to pathogens, preventing tissue damage through PRR-induced inhibitory signals, opsonization of pathogen-associated molecular patterns, and attenuation of injurious leukocyte responses. The inducibility of these protective responses has prompted attempts to therapeutically harness epithelial defense mechanisms to protect against pneumonias. Recent reports describe successful strategies for manipulation of epithelial defenses to protect against a wide range of respiratory pathogens. The lung epithelium is capable of both significant antimicrobial responses that reduce pathogen burdens and tolerance mechanisms that attenuate immunopathology. This manuscript reviews inducible lung epithelial defense mechanisms that offer opportunities for therapeutic manipulation to protect vulnerable populations against pneumonia.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

Impact of prophylactic CpG Oligodeoxynucleotide application on implant-associated Staphylococcus aureus bone infection

TLR-9 ligand CpG oligodeoxynucleotide type B (CpG ODN) induces a proinflammatory environment. We evaluated the effects of a preoperative CpG ODN application in an implant-associated Staphylococcus aureus bone infection model by monitoring bacterial loads and cytokine and chemokine levels. A total of 95 rats were used in four different groups: CpG ODN group (group 1; n=25), non-CpG-ODN group (group 2; n=25); saline pretreatment (group 3; n=25), and one uninfected group (group 4; n=20). A single dose of CpG-ODN was administered to the left tibialis anterior muscle 3days prior to surgery and the tibia midshaft was osteotomized, stabilized by an intramedullary implant and subsequently contaminated with 10(3) colony forming units (CFUs) of S. aureus in groups 1-3. The osteotomy gap in animals of group 4 was not contaminated with S. aureus and those animals did not receive any pretreatment. CpG ODN administration resulted in significant reduction of the bacterial load in tibia tissue homogenate and on the implant surface on day 1 post-infection compared to non-CpG-ODN pretreatment (p<0.05; p<0.05). Reductions in bacterial CFUs, compared to non-treated (saline) controls, were approximately 67% and 77% for bone tissue homogenates and implants. No bacteria were detected in uninfected rats. Early reduction of bacterial CFUs in the tibia was accompanied by increased levels of proinflammatory mediators MIP-2, IL-1β and RANTES in bone tissue milieu of the CpG ODN treated group compared to controls. At day 42 post-infection, bone marrow tissue of rats pretreated with CpG ODN had comparable high bacterial CFU numbers as the non-CpG ODN or saline treated groups. Microbiological analysis of implants removed from CpG ODN treated rats showed high bacterial growth densities on their surfaces which were not different from those observed in controls. In histology, all animals of groups 1-3 showed established infected non-unions. Additionally, inflammatory mediator profiles in bone marrow homogenates of CpG ODN treated rats resembled those seen in infected controls. In this rat model, prophylactic administration of a single dose of CpG ODN, resulted in marked reduction of S. aureus load in the infected tibia during the initial stage of infection but failed to prevent development of chronic infection over time.

Leishmania tarentolae secreting the sand fly salivary antigen PpSP15 confers protection against Leishmania major infection in a susceptible BALB/c mice model

Cutaneous leishmaniasis is a zoonotic, vector-borne disease causing a major health problem in several countries. No vaccine is available and there are limitations associated with the current therapeutic regimens. Immune responses to sand fly saliva have been shown to protect against Leishmania infection. A cellular immune response to PpSP15, a protein from the sand fly Phlebotomus papatasi, was sufficient to control Leishmania major infection in mice. This work presents data supporting the vaccine potency of recombinant live non-pathogenic Leishmania (L.) tarentolae secreting PpSP15 in mice and its potential as a new vaccine strategy against L. major. We generated a recombinant L. tarentolae-PpSP15 strain delivered in the presence of CpG ODN and evaluated its immunogenicity and protective immunity against L. major infection in BALB/c mice. In parallel, different vaccination modalities using PpSP15 as the target antigen were compared. Humoral and cellular immune responses were evaluated before and at three and eight weeks after challenge. Footpad swelling and parasite load were assessed at eight and eleven weeks post-challenge. Our results show that vaccination with L. tarentolae-PpSP15 in combination with CpG as a prime-boost modality confers strong protection against L. major infection that was superior to other vaccination modalities used in this study. This approach represents a novel and promising vaccination strategy against Old World cutaneous leishmaniasis.

Functional Genomic Screen Identifies Klebsiella pneumoniae Factors Implicated in Blocking Nuclear Factor κB (NF-κB) Signaling

Klebsiella pneumoniae is an etiologic agent of community-acquired and nosocomial pneumonia. It has been shown that K. pneumoniae infections are characterized by reduced early inflammatory response. Recently our group has shown that K. pneumoniae dampens the activation of inflammatory responses by antagonizing the activation of the NF-κB canonical pathway. Our results revealed that K. pneumoniae capsule polysaccharide (CPS) was necessary but not sufficient to attenuate inflammation. To identify additional Klebsiella factors required to dampen inflammation, we standardized and applied a high-throughput gain-of-function screen to examine a Klebsiella transposon mutant library. We identified 114 mutants that triggered the activation of NF-κB. Two gene ontology categories accounted for half of the loci identified in the screening: metabolism and transport genes (32% of the mutants) and envelope-related genes (17%). Characterization of the mutants revealed that the lack of the enterobactin siderophore was linked to a reduced CPS expression, which in turn underlined the NF-κB activation induced by the mutant. The lipopolysaccharide (LPS) O-polysaccharide and the pullulanase (PulA) type 2 secretion system (T2SS) are required for full effectiveness of the immune evasion. Importantly, these factors do not play a redundant role. The fact that LPS O-polysaccharide and T2SS mutant-induced responses were dependent on TLR2-TLR4-MyD88 activation suggested that LPS O-polysaccharide and PulA perturbed Toll-like receptor (TLR)-dependent recognition of K. pneumoniae. Finally, we demonstrate that LPS O-polysaccharide and pulA mutants are attenuated in the pneumonia mouse model. We propose that LPS O-polysaccharide and PulA T2SS could be new targets for the design of new antimicrobials. Increasing TLR-governed defense responses might provide also selective alternatives for the management of K. pneumoniae pneumonia.

Intramuscular administration of a synthetic CpG-oligodeoxynucleotide modulates functional responses of neutrophils of neonatal foals

Neutrophils play an important role in protecting against infection. Foals have age-dependent deficiencies in neutrophil function that may contribute to their predisposition to infection. Thus, we investigated the ability of a CpG-ODN formulated with Emulsigen to modulate functional responses of neutrophils in neonatal foals. Eighteen foals were randomly assigned to receive either a CpG-ODN with Emulsigen (N = 9) or saline intramuscularly at ages 1 and 7 days. At ages 1, 3, 9, 14, and 28, blood was collected and neutrophils were isolated from each foal. Neutrophils were assessed for basal and Rhodococcus equi-stimulated mRNA expression of the cytokines interferon-γ (IFN-γ), interleukin (IL)-4, IL-6, and IL-8 using real-time PCR, degranulation by quantifying the amount of β-D glucuronidase activity, and reactive oxygen species (ROS) generation using flow cytometry. In vivo administration of the CpG-ODN formulation on days 1 and 7 resulted in significantly (P<0.05) increased IFN-γ mRNA expression by foal neutrophils on days 3, 9, and 14. Degranulation was significantly (P<0.05) lower for foals in the CpG-ODN-treated group than the control group at days 3 and 14, but not at other days. No effect of treatment on ROS generation was detected. These results indicate that CpG-ODN administration to foals might improve innate and adaptive immune responses that could protect foals against infectious diseases and possibly improve responses to vaccination.

Comparison of the protective effects of killed Burkholderia pseudomallei and CpG oligodeoxynucleotide against live challenge

Melioidosis is a fatal disease caused by Burkholderia pseudomallei. Currently there is no vaccine available. Synthetic oligodeoxynucleotides with unmethylated CpG dinucleotide motifs (CpG ODN) can stimulate vertebrate immune cells and clear certain pathogens that are susceptible to a strong Th1 response. In our previous study, pretreatment with CpG ODN alone or CpG-ODN with cationic liposomes for 2-10 or 30 days before B. pseudomallei infection in mice conferred 80-100% protection. In the present study we investigated the protective effect of CpG-ODN together with heat-killed (HK) or paraformaldehyde-killed B. pseudomallei (PP). HK or PP were used to immunize BALB/c mice twice at 15-day intervals before intra-peritoneal challenge with 5LD50 of B. pseudomallei and observed for 30 days. We found that PP could significantly protect mice (60%) with an increased survival time (24.8±11.63 days) while in the HK and PBS groups, all infected mice died within 6 days. Although either CpG ODN or PP conferred significant protection, giving them in combination did not enhance it further. Serum IFN-γ levels on day-5 (before challenge) of the PP and PP+CpG ODN groups were significantly higher than those of the PBS control group. The results further support the importance of IFN-γ in host protection against B. pseudomallei and suggest further study on paraformaldehyde-killed bacteria as a component of a future B. pseudomallei vaccine.

CpG oligodeoxynucleotide protect neonatal piglets from challenge with the enterotoxigenic E. coli

CpG motifs activates mammalian lymphocytes and macrophages to produce cytokines and polyclonal Ig. These include IFN-γ, IL-12, TNF-a, which are important in the control of bacterial infection. But thus far, the innate immunostimulatory effects of CpG ODN against pathogen have been established mainly in mouse, monkey, sheep, chicken, but not in neonatal piglets. The purpose of this study is to determine the potential protection of CpG ODN against enterotoxigenic Escherichia coli (ETEC) (with which neonatal piglets were susceptible to infection in our lab) in neonatal piglets. Here, we show intranasal (IN)-mucosal and intramuscularly (IM) systemic administration of CpG ODN could enhance innate cellular (cytokine) immunity in the sera and intestine mucosa post challenge, and thereafter the development of antigen-specific antibodies in piglets. IN and IM immunizations of neonatal piglets without antigen both reduced the ETEC excretion and alleviated diarrhoea symptoms upon challenge, and IN route had better protection effects than IM route. Protection in this study was linked to induction of a Th1 response which induced by CpG ODN. Co-delivery with Emulsigen (EM), could improve protection mediated by CpG ODN. These observations indicate that IN administration of 100 μg/kg CpG ODN with 20% EM codelivery may represent a valuable strategy for induction of innate immunity against ETEC infection in neonatal piglets.

Allergic airway inflammation decreases lung bacterial burden following acute Klebsiella pneumoniae infection in a neutrophil- and CCL8-dependent manner

The Th17 cytokines interleukin-17A (IL-17A), IL-17F, and IL-22 are critical for the lung immune response to a variety of bacterial pathogens, including Klebsiella pneumoniae. Th2 cytokine expression in the airways is a characteristic feature of asthma and allergic airway inflammation. The Th2 cytokines IL-4 and IL-13 diminish ex vivo and in vivo IL-17A protein expression by Th17 cells. To determine the effect of IL-4 and IL-13 on IL-17-dependent lung immune responses to acute bacterial infection, we developed a combined model in which allergic airway inflammation and lung IL-4 and IL-13 expression were induced by ovalbumin sensitization and challenge prior to acute lung infection with K. pneumoniae. We hypothesized that preexisting allergic airway inflammation decreases lung IL-17A expression and airway neutrophil recruitment in response to acute K. pneumoniae infection and thereby increases the lung K. pneumoniae burden. As hypothesized, we found that allergic airway inflammation decreased the number of K. pneumoniae-induced airway neutrophils and lung IL-17A, IL-17F, and IL-22 expression. Despite the marked reduction in postinfection airway neutrophilia and lung expression of Th17 cytokines, allergic airway inflammation significantly decreased the lung K. pneumoniae burden and postinfection mortality. We showed that the decreased lung K. pneumoniae burden was independent of IL-4, IL-5, and IL-17A and partially dependent on IL-13 and STAT6. Additionally, we demonstrated that the decreased lung K. pneumoniae burden associated with allergic airway inflammation was both neutrophil and CCL8 dependent. These findings suggest a novel role for CCL8 in lung antibacterial immunity against K. pneumoniae and suggest new mechanisms of orchestrating lung antibacterial immunity.

Vaccine approaches for multidrug resistant Gram negative infections

Multidrug resistant (MDR) Gram negative bacterial infections are increasing in frequency and are associated with significant financial costs, morbidity and mortality. Current antibiotic therapies are associated with unacceptably poor clinical outcomes and toxicity. Unfortunately, the development of novel antimicrobials is stagnant leaving a significant clinical need for alternative treatments of MDR Gram negative rod infections. Recent preclinical studies have identified Th17 cells as critical mediators of broadly protective adaptive immunity, including protection against MDR infections. Studies of Th17 eliciting antigens, adjuvants and routes of immunization have identified potential vaccine strategies that may confer long-lived adaptive immunity against MDR Gram negative bacterial infections.

Toll-like receptor 9 signaling delays neutrophil apoptosis by increasing transcription of Mcl-1

Neutrophils detect bacterial constituents, including bacterial DNA (CpG DNA), which elicits innate immunity and prolongs the functional life span of neutrophils through suppression of apoptosis. Both the anti-apoptotic protein Mcl-1 and activation of NF-κB have been implicated in neutrophil survival, but there is no evidence that these are linked in neutrophils. We hypothesized that CpG DNA could simultaneously activate these pathways. High purity CpG DNA (0.4–3.2 µg/ml) extended the life span of human neutrophils in vitro by delaying apoptosis through altering the rate of Mcl-1 turnover. CpG DNA slightly decreased Mcl-1 protein level in the presence of cyclohexmide and the proteasome inhibitor MG132 had little effect on Mcl-1 expression in CpG DNA-treated neutrophils. In contrast, CpG DNA evoked rapid increases in DNA binding by NF-κB/p65 and Mcl-1 mRNA. NF-κB inhibitors and the telomere-derived TLR9 inhibitory oligonucleotide 5′-TTT AGG GTT AGG GTT AGG G-3′ markedly reduced Mcl-1 protein levels and subsequently abrogated suppression of apoptosis by CpG DNA. Furthermore, CpG DNA attenuated the decreases in Mcl-1 in both cell lysate and nucleus of neutrophils undergoing spontaneous apoptosis and increased Mcl-1 translocation to the mitochondria, leading to preservation of mitochondrial transmembrane potential. These results demonstrate that CpG DNA through toll-like receptor 9 links two survival signaling pathways by delaying apoptosis through induction of NF-κB-mediated Mcl-1 gene transcription and promoting Mcl-1 translocation to the mitochondria.

Immunotherapeutic potential of CpG oligodeoxynucleotides in veterinary species

Innate immunity plays a critical role in host defense against infectious diseases by discriminating between self and infectious non-self. The recognition of infectious non-self involves germ-line encoded pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs). The PAMPs are the components of pathogenic microbes which include not only the cell wall constituents but also the unmethylated 2'-deoxy-ribo-cytosine-phosphate-guanosine (CpG) motifs. These CpG motifs present within bacterial and viral DNA are recognized by toll-like receptor 9 (TLR9), and signaling by this receptor triggers a proinflammatory cytokine response which, in turn, influences both innate and adaptive immune responses. The activation of TLR9 with synthetic CpG oligodeoxynucleotides (ODNs) induces powerful Th1-like immune responses. It has been shown to provide protection against infectious diseases, allergy and cancer in laboratory animal models and some domestic animal species. With better understanding of the basic biology and immune mechanisms, it would be possible to exploit the potential of CpG motifs for animal welfare. The research developments in the area of CpG and TLR9 and the potential applications in animal health have been reviewed in this article.

Liposomal antibiotics for the treatment of infectious diseases

INTRODUCTION

Liposomal delivery systems have been utilized in developing effective therapeutics against cancer and targeting microorganisms in and out of host cells and within biofilm community. The most attractive feature of liposome-based drugs are enhancing therapeutic index of the new or existing drugs while minimizing their adverse effects.

AREAS COVERED

This communication provides an overview on several aspects of liposomal antibiotics including the most widely used preparation techniques for encapsulating different agents and the most important characteristic parameters applied for examining shape, size and stability of the spherical vesicles. In addition, the routes of administration, liposome-cell interactions and host parameters affecting the biodistribution of liposomes are highlighted.

EXPERT OPINION

Liposomes are safe and suitable for delivery of variety of molecules and drugs in biomedical research and medicine. They are known to improve the therapeutic index of encapsulated agents and reduce drug toxicity. Recent studies on liposomal formulation of chemotherapeutic and bioactive agents and their targeted delivery show liposomal antibiotics potential in the treatment of microbial infections.

Modeling Klebsiella pneumoniae pathogenesis by infection of the wax moth Galleria mellonella

The implementation of infection models that approximate human disease is essential for understanding pathogenesis at the molecular level and for testing new therapies before they are entered into clinical stages. Insects are increasingly being used as surrogate hosts because they share, with mammals, essential aspects of the innate immune response to infections. We examined whether the larva of the wax moth Galleria mellonella could be used as a host model to conceptually approximate Klebsiella pneumoniae-triggered pneumonia. We report that the G. mellonella model is capable of distinguishing between pathogenic and nonpathogenic Klebsiella strains. Moreover, K. pneumoniae infection of G. mellonella models some of the known features of Klebsiella-induced pneumonia, i.e., cell death associated with bacterial replication, avoidance of phagocytosis by phagocytes, and the attenuation of host defense responses, chiefly the production of antimicrobial factors. Similar to the case for the mouse pneumonia model, activation of innate responses improved G. mellonella survival against subsequent Klebsiella challenge. Virulence factors necessary in the mouse pneumonia model were also implicated in the Galleria model. We found that mutants lacking capsule polysaccharide, lipid A decorations, or the outer membrane proteins OmpA and OmpK36 were attenuated in Galleria. All mutants activated G. mellonella defensive responses. The Galleria model also allowed us to monitor Klebsiella gene expression. The expression levels of cps and the loci implicated in lipid A remodeling peaked during the first hours postinfection, in a PhoPQ- and PmrAB-governed process. Taken together, these results support the utility of G. mellonella as a surrogate host for assessing infections with K. pneumoniae.

T cell-mediated host immune defenses in the lung

Evidence has increasingly shown that the lungs are a major site of immune regulation. A robust and highly regulated immune response in the lung protects the host from pathogen infection, whereas an inefficient or deleterious response can lead to various pulmonary diseases. Many cell types, such as epithelial cells, dendritic cells, macrophages, neutrophils, eosinophils, and B and T lymphocytes, contribute to lung immunity. This review focuses on the recent advances in understanding how T lymphocytes mediate pulmonary host defenses against bacterial, viral, and fungal pathogens.

Intranasal prophylaxis with CpG oligodeoxynucleotide can protect against Yersinia pestis infection

Immunomodulatory agents potentially represent a new class of broad-spectrum antimicrobials. Here, we demonstrate that prophylaxis with immunomodulatory cytosine-phosphate-guanidine (CpG) oligodeoxynucleotide (ODN), a toll-like receptor 9 (TLR9) agonist, confers protection against Yersinia pestis, the etiologic agent of plague. The data establish that intranasal administration of CpG ODN 1 day prior to lethal pulmonary exposure to Y. pestis strain KIM D27 significantly improves survival of C57BL/6 mice and reduces bacterial growth in hepatic tissue, despite paradoxically increasing bacterial growth in the lung. All of these CpG ODN-mediated impacts, including the increased pulmonary burden, are TLR9 dependent, as they are not observed in TLR9-deficient mice. The capacity of prophylactic intranasal CpG ODN to enhance survival does not require adaptive immunity, as it is evident in mice lacking B and/or T cells; however, the presence of T cells improves long-term survival. The prophylactic regimen also improves survival and reduces hepatic bacterial burden in mice challenged intraperitoneally with KIM D27, indicating that intranasal delivery of CpG ODN has systemic impacts. Indeed, intranasal prophylaxis with CpG ODN provides significant protection against subcutaneous challenge with Y. pestis strain CO92 even though it fails to protect mice from intranasal challenge with that fully virulent strain.

Monitoring Therapeutic Treatments against Burkholderia Infections Using Imaging Techniques

Burkholderia mallei, the etiologic agent of glanders, are Category B select agents with biothreat potential, and yet effective therapeutic treatments are lacking. In this study, we showed that CpG administration increased survival, demonstrating protection in the murine glanders model. Bacterial recovery from infected lungs, liver and spleen was significantly reduced in CpG-treated animals as compared with non-treated mice. Reciprocally, lungs of CpG-treated infected animals were infiltrated with higher levels of neutrophils and inflammatory monocytes, as compared to control animals. Employing the B. mallei bioluminescent strain CSM001 and the Neutrophil-Specific Fluorescent Imaging Agent, bacterial dissemination and neutrophil trafficking were monitored in real-time using multimodal in vivo whole body imaging techniques. CpG-treatment increased recruitment of neutrophils to the lungs and reduced bioluminescent bacteria, correlating with decreased bacterial burden and increased protection against acute murine glanders. Our results indicate that protection of CpG-treated animals was associated with recruitment of neutrophils prior to infection and demonstrated, for the first time, simultaneous real time in vivo imaging of neutrophils and bacteria. This study provides experimental evidence supporting the importance of incorporating optimized in vivo imaging methods to monitor disease progression and to evaluate the efficacy of therapeutic treatment during bacterial infections.

Anti-tumor activity of CpG-ODN aerosol in mouse lung metastases

Studies in preclinical models have demonstrated the superior anti-tumor effect of CpG oligodeoxynucleotides (CpG-ODN) when administered at the tumor site rather than systemically. We evaluated the effect of aerosolized CpG-ODN on lung metastases in mice injected with immunogenic N202.1A mammary carcinoma cells or weakly immunogenic B16 melanoma cells. Upon reaching the bronchoalveolar space, aerosolized CpG-ODN activated a local immune response, as indicated by production of IL-12p40, IFN-γ and IL-1β and by recruitment and maturation of DC cells in bronchoalveolar lavage fluid of mice. Treatment with aerosolized CpG-ODN induced an expansion of CD4+ cells in lung and was more efficacious than systemic i.p. administration against experimental lung metastases of immunogenic N202.1A mammary carcinoma cells, whereas only i.p. delivery of CpG-ODN provided anti-tumor activity, which correlated with NK cell expansion in the lung, against lung metastases of the poorly immunogenic B16 melanoma. The inefficacy of aerosol therapy to induce NK expansion was related to the presence of immunosuppressive macrophages in B16 tumor-bearing lungs, as mice depleted of these cells by clodronate treatment responded to aerosol CpG-ODN through expansion of the NK cell population and significantly reduced numbers of lung metastases. Our results indicate that tumor immunogenicity and the tumor-induced immunosuppressive environment are critical factors to the success of CpG therapy in the lung, and point to the value of routine sampling of the lung immune environment in defining an optimal immunotherapeutic strategy.

Stimulation with a class A CpG oligonucleotide enhances resistance to infection with feline viruses from five different families

Domestic cats are commonly affected by viral pathogens that induce lengthy infections with fatal outcomes. Prevention of viral propagation is of primordial importance in shelters and catteries, where cats from different backgrounds have narrow contacts. Oligonucleotides (ODN) containing cytosine-phosphate-guanosine motifs of class A (CpG-A) are highly potent synthetic inducers of innate antiviral mechanisms. The aim of this study was to test their ability to modulate innate immune responses and prevent viral replication as stand-alone agents in the domestic cat. CpG-A stimulation of feline peripheral blood mononuclear cells (PBMCs) enhanced their proliferation, increased the presence of co-stimulatory molecules on their surface and influenced their gene expression profiles in an antiviral orientation. Incubation of the supernatants of CpG-A stimulated PBMCs with feline cell lines of epithelial and fibroblastic origin induced expression of the antiviral myxovirus resistance (Mx) gene in these target cells, which also showed enhanced resistance to feline viruses from five distinct families, namely Coronaviridae, Herpesviridae, Caliciviridae, Parvoviridae, and Retroviridae. Most importantly, subcutaneous administration of CpG-A in domestic cats systemically increased the expression of Mx, reaching maximal levels within 24 h. Plasma from treated cats could furthermore inhibit viral replication in vitro. Altogether, our data highlight the promising potential of CpG-A to induce a preventive antiviral state in the cat and to protect feline populations against a broad range of virus infections.

Cationic liposomes extend the immunostimulatory effect of CpG oligodeoxynucleotide against Burkholderia pseudomallei infection in BALB/c mice

Melioidosis is a severe disease caused by the Gram-negative bacterium Burkholderia pseudomallei. Previously we showed that pretreatment of mice with CpG oligodeoxynucleotide (CpG ODN) 2 to 10 days prior to B. pseudomallei challenge conferred as high as 90% protection, but this window of protection was rather short. In the present study, we therefore aimed to prolong this protective window and to gain further insight into the mechanisms underlying the protection induced by CpG ODN against B. pseudomallei infection. It was found that the CpG ODN incorporated with cationic liposomes (DOTAP) but not zwitterionic liposomes (DOPC) provided complete protection against bacterial challenge. Although marked elevation of gamma interferon (IFN-γ) was found in the infected animals 2 days postinfection, it was significantly lowered by the DOTAP-plus-CpG ODN pretreatment. When appropriately activated, the phagocytic index and oxidative burst responses of neutrophils appeared not to be elevated. However, macrophages from stimulated mice showed higher levels of nitric oxide production and exhibited higher levels of antimicrobial activities, judging from lower numbers of viable intracellular bacteria. Taken together, our results demonstrate that DOTAP can enhance the protective window period of CpG ODN to at least 30 days and provide 100% protection against B. pseudomallei infection. The protective effect of DOTAP plus CpG ODN could provide an alternative approach to preventing this lethal infection, for which no vaccine is yet available.

Combining vaccination and postexposure CpG therapy provides optimal protection against lethal sepsis in a biodefense model of human melioidosis

The Gram-negative bacterium Burkholderia pseudomallei is the causative agent of melioidosis, a major cause of lethal sepsis and morbidity in endemic areas of Southeast Asia and a potential bioterrorism threat. We have used susceptible BALB/c mice to evaluate the potential of targeting vaccination and generic immunotherapy to the lung for optimal protection against respiratory challenge. Intranasal vaccination with live attenuated B. pseudomallei increased survival and induced interferon-γ-secreting T cells in the lung. Intranasal delivery of CpG oligodeoxynucleotides also provided significant protection; however, combining preexposure vaccination with CpG treatment at the time of infection or up to 18 hours after infection, provided significantly greater protection than either treatment alone. This combination prolonged survival, decreased bacterial loads by >1000-fold, and delayed the onset of sepsis. This novel approach may be applicable to other potential biodefense agents for which existing countermeasures are not fully effective.

Inhaled innate immune ligands to prevent pneumonia

Epithelial surfaces throughout the body continuously sample and respond to environmental stimuli. The accessibility of lung epithelium to inhaled therapies makes it possible to stimulate local antimicrobial defences with aerosolized innate immune ligands. This strategy has been shown to be effective in preclinical models, as delivery of innate immune ligands to the lungs of laboratory animals results in protection from subsequent challenge with microbial pathogens. Survival of the animal host in this setting correlates directly with killing of pathogens within the lungs, indicating the induction of a resistance mechanism. Resistance appears to be mediated primarily by activated epithelial cells rather than recruited leucocytes. Resistance reaches a peak within hours and persists for several days. Innate immune ligands can interact synergistically under some circumstances, and synergistic combinations of innate ligands delivered by aerosol are capable of inducing a high level of broad host resistance to bacteria, fungi and viruses. The induction of innate antimicrobial resistance within the lungs could have clinical applications in the prevention of lower respiratory tract infection in subjects transiently at high risk. These include cancer patients undergoing myeloablative chemotherapy, intubated patients being mechanically ventilated, vulnerable individuals during seasonal influenza epidemics, asthmatic subjects experiencing a respiratory viral infection, and healthy subjects exposed to virulent pathogens from a bioterror attack or emergent pandemic. In summary, stimulation of the lung epithelium to induce localized resistance to infection is a novel strategy whose clinical utility will be assessed in the near future.

Synergistic interactions of TLR2/6 and TLR9 induce a high level of resistance to lung infection in mice

Infectious pneumonias exact an unacceptable mortality burden worldwide. Efforts to protect populations from pneumonia have focused historically on antibiotic development and vaccine-enhanced adaptive immunity. However, we have reported recently that the lungs' innate defenses can be induced therapeutically by inhalation of a bacterial lysate that protects mice against otherwise lethal pneumonia. In this study, we tested in mice the hypothesis that TLRs are required for this antimicrobial phenomenon and found that resistance could not be induced in the absence of the TLR signaling adaptor protein MyD88. We then attempted to recapitulate the protection afforded by the bacterial lysate by stimulating the lung epithelium with aerosolized synthetic TLR ligands. Although most single or combination treatments yielded no protection, simultaneous treatment with ligands for TLR2/6 and TLR9 conferred robust, synergistic protection against virulent gram-positive and gram-negative pathogens. Protection was associated with rapid pathogen killing in the lungs, and pathogen killing could be induced from lung epithelial cells in isolation. Taken together, these data demonstrate the requirement for TLRs in inducible resistance against pneumonia, reveal a remarkable, unanticipated synergistic interaction of TLR2/6 and TLR9, reinforce the emerging evidence supporting the antimicrobial capacity of the lung epithelium, and may provide the basis for a novel clinical therapeutic that can protect patients against pneumonia during periods of peak vulnerability.

Klebsiella pneumoniae-triggered DC recruit human NK cells in a CCR5-dependent manner leading to increased CCL19-responsiveness and activation of NK cells

Besides their role in destruction of altered self-cells, NK cells have been shown to potentiate T-cell responses by interacting with DC. To take advantage of NK-DC crosstalk in therapeutic DC-based vaccination for infectious diseases and cancer, it is essential to understand the biology of this crosstalk. We aimed to elucidate the in vitro mechanisms responsible for NK-cell recruitment and activation by DC during infection. To mimic bacterial infection, DC were exposed to a membrane fraction of Klebsiella pneumoniae, which triggers TLR2/4. DC matured with these bacterial fragments can actively recruit NK cells in a CCR5-dependent manner. An additional mechanism of DC-induced NK-cell recruitment is characterized by the induction of CCR7 expression on CD56(dim) CD16(+) NK cells after physical contact with membrane fraction of K. pneumoniae-matured DC, resulting in an enhanced migratory responsiveness to the lymph node-associated chemokine CCL19. Bacterial fragment-matured DC do not only mediate NK-cell migration but also meet the prerequisites needed for augmentation of NK-cell cytotoxicity and IFN-γ production, the latter of which contributes to Th1 polarization.

CpG oligodeoxynucleotide promotes protective immunity in the enteric mucosa and suppresses enterotoxigenic E. coli in the weaning piglets

CpG oligodeoxynucleotide (CpG ODN) has been described as an effective activator of the innate immune system, with potential to protect against infection caused by a range of pathogens in a non-specific manner. We therefore investigated if intranasal (IN), oral (OR)-mucosal, and intramuscular (IM)-systemic administrations of CpG ODN without antigen codelivery could all enhance innate immunity in the enteric mucosa and control the extent of enterotoxigenic Escherichia coli (ETEC) infection in weaning piglets. Here our data showed that CpG ODN dosed by IN, OR or IM routes protected weaning piglets against a subsequent challenge with ETEC. The level of protection was greater when CpG ODN was administered IN and OR than IM, demonstrating a clear relationship between the route of CpG dosing and protection. IN and OR treatments with CpG ODN reduced bacterial load in the phases at days 3-5 post challenge. The CXC chemokine (CXCL10 and CXCL11) and CC chemokine (CCL4 and CCL5) mRNA expressions were elevated in the intestinal tissues from animals treated IN or OR with CpG ODN compared to untreated controls. Significantly enhanced mRNA expressions for cathelicidins (PR-39 and protegrin-1), but moderately for β-defensin (pBD1 and pBD2), were observed in IN or OR CpG-treatments. Also, significant production of cytokines (IL-12, IFN-γ, and MCP-1) and F4-specific antibodies (IgG/IgA) was detected in intestinal washings following IN and OR CpG-treatments. In contrast, IM delivery induced marked production of sera F4-specific antibodies. It was possible that these chemokines, cytokines, cathelicidins and antibodies played a role in the clearance of ETEC. These findings suggested that IN or OR administration of CpG ODN without antigen codelivery might represent a valuable strategy for induction of innate immunity against ETEC infection.

Subcutaneous, but not intratracheal administration of the TLR9 agonist, CpG DNA transiently reduces parainfluenza-3 virus shedding in newborn lambs

Synthetic oligodeoxynucleotides (ODN) containing CpG motifs signal through TLR9 and activate innate immunity resulting in protection against a variety of parasitic, bacterial and viral pathogens in mouse models. However, few studies have demonstrated protection in humans and large animals. In the present investigations, we evaluated protection by CpG ODN in a parainfluenza-3 (PI-3) virus infection in neonatal lambs. Subcutaneous (SC) injection of CpG ODN induced high levels of 2'5'-A synthetase and significantly reduced PI-3 virus shedding in newborn lambs. Furthermore, pre-treatment of newborn lambs with SC CpG ODN 2 days, but not 6 days prior to the virus challenge was protective. In contrast, intratracheal (IT) administration of CpG ODN induced 2'5'-A synthetase but had no significant impact on PI-3 virus shedding in nasal secretions. We conclude that a systemic administration of CpG ODN and the timing of the treatment are critical for the protection of neonatal lambs against a respiratory viral infection.

Inducible innate resistance of lung epithelium to infection

Most studies of innate immunity have focused on leukocytes such as neutrophils, macrophages, and natural killer cells. However, epithelial cells play key roles in innate defenses that include providing a mechanical barrier to microbial entry, signaling to leukocytes, and directly killing pathogens. Importantly, all these defenses are highly inducible in response to the sensing of microbial and host products. In healthy lungs, the level of innate immune epithelial function is low at baseline. This is indicated by low levels of spontaneous microbial killing and cytokine release, reflecting low constitutive stimulation in the nearly sterile lower respiratory tract when mucociliary clearance mechanisms are functioning effectively. This contrasts with the colon, where bacteria are continuously present and epithelial cells are constitutively activated. Although the surface area of the lungs presents a large target for microbial invasion, activated lung epithelial cells that are closely apposed to deposited pathogens are ideally positioned for microbial killing.

Functional genomics to identify therapeutic prophylactic targets

Infectious diseases are a leading cause of global human mortality. The use of antimicrobials remains the most common strategy for treatment. However, the isolation of pathogens resistant to virtually all antimicrobials makes it urgent to develop effective therapeutics based on new targets. Here we review a new drug discovery paradigm focusing on identifying and targeting host factors important for infection as well as pathogen determinants involved in disease progression. We summarize innovative strategies which by combining bioinformatics with transcriptomics and chemical genetics have already identified host factors essential for pathogen entry, survival and replication. We describe how the discovery of RNA interference which allows loss-of-function studies has facilitated functional genomic studies in human cells. It is expected that these studies will identify targets to be used as host-directed drug therapy which, together with antimicrobials targeting microbial virulence factors, will efficiently eliminate the invading pathogen.

Cooperative interactions between TLR4 and TLR9 regulate interleukin 23 and 17 production in a murine model of gram negative bacterial pneumonia

Toll like receptors play an important role in lung host defense against bacterial pathogens. In this study, we investigated independent and cooperative functions of TLR4 and TLR9 in microbial clearance and systemic dissemination during Gram-negative bacterial pneumonia. To access these responses, wildtype Balb/c mice, mice with defective TLR4 signaling (TLR4^lps-d), mice deficient in TLR9 (TLR9^−/−) and TLR4/9 double mutant mice (TLR4^lps-d/TLR9^−/−) were challenged with K. pneumoniae, then time-dependent lung bacterial clearance and systemic dissemination determined. We found impaired lung bacterial clearance in TLR4 and TLR9 single mutant mice, whereas the greatest impairment in clearance was observed in TLR4^lps-d/TLR9^−/− double mutant mice. Early lung expression of TNF-α, IL-12, and chemokines was TLR4 dependent, while IFN-γ production and the later expression of TNF-α and IL-12 was dependent on TLR9. Classical activation of lung macrophages and maximal induction of IL-23 and IL-17 required both TLR4 and TLR9. Finally, the i.t. instillation of IL-17 partially restored anti-bacterial immunity in TLR4^lps-d/TLR9^−/− double mutant mice. In conclusion, our studies indicate that TLR4 and TLR9 have both non-redundant and cooperative roles in lung innate responses during Gram-negative bacterial pneumonia and are both critical for IL-17 driven antibacterial host response.

Innate immune recognition in infectious and noninfectious diseases of the lung

Diseases of the respiratory tract are among the leading causes of death in the world population. Increasing evidence points to a key role of the innate immune system with its pattern recognition receptors (PRRs) in both infectious and noninfectious lung diseases, which include pneumonia, chronic obstructive pulmonary disease, acute lung injury, pneumoconioses, and asthma. PRRs are capable of sensing different microbes as well as endogenous molecules that are released after cell damage. This PRR engagement is the prerequisite for the initiation of immune responses to infections and tissue injuries which can be beneficial or detrimental to the host. PRRs include the Toll-like receptors, NOD-like receptors, RIG-I-like receptors, and cytosolic DNA sensors. The PRRs and their signaling pathways represent promising targets for prophylactic and therapeutic interventions in various lung diseases.

The development and preliminary evaluation of a new Mycobacterium tuberculosis vaccine comprising Ag85b, HspX and CFP-10:ESAT-6 fusion protein with CpG DNA and aluminum hydroxide adjuvants

Ag85b and HspX of Mycobacterium tuberculosis (Mtb) (H37Rv) were expressed and purified in this study. These two proteins were combined with another fusion protein CFP-10:ESAT-6 (C/E) (Ag), then mixed with the adjuvants CpG DNA and aluminum hydroxide and used to vaccinate mice and guinea pigs challenged with Mtb (H37Rv). The number of spleen lymphocytes secreting Ag85b, HspX and C/E-specific interferon-gamma were significantly higher in the Ag+Al+CpG group than in the Ag and CpG groups. The combination of Ag, Al and CpG induced the highest concentrations of anti-Ag85b, anti-HspX and anti-C/E immunoglobulin G in mouse serum. Mouse peritoneal macrophages from the Ag+Al+CpG group secreted significantly higher levels of interleukin-12 compared with macrophages from the other groups. The total mean liver, lung and spleen lesion scores and bacterial loads in the spleen in guinea pigs vaccinated with Ag+Al+CpG were lower than those of the other groups, but no significant difference was found. These results show that the mixture of Ag85b, HspX and C/E with a combination of CpG and aluminum adjuvants can induce both humoral and cellular immune responses in mice, whereas it plays only a small role in the control of disease progression in guinea pigs challenged with Mtb.

All three classes of CpG ODNs up-regulate IP-10 gene in pigs

The analysis of CpG ODN induced innate immune responses in different animal species has shown substantial similarities and differences in levels and types of induced cytokines profile. The objectives of these studies were to identify innate immune biomarkers activated by three classes of CpG ODNs in pigs. For this purpose, we investigated the kinetics of innate immune responses in immune cells from pigs following in vitro and in vivo stimulation with CpG ODNs. The mRNA expression of cytokine and chemokine genes were assayed by SYBR green based quantitative real time PCR. A-class CpG ODN induced significant but transient levels of IFN-gamma, IL-12 (P40), IL-6, IL-4 and TNF-alpha mRNA, C-class CpG ODN induced significant level of IFN-gamma, IFN-alpha and IL-12 mRNA and the lowest level of IL-4 (Th-2 type) mRNA. A very low level of some cytokines stimulation was observed by GC ODNs. It is noteworthy, that IL-12 (P35) mRNA was significantly stimulated by B-class GpC ODN 7909. Interestingly, all classes of CpG ODNs induced significant level of IP-10 at 12h post stimulation. These in vitro and in vivo observations suggest that interferon-gamma inducible protein 10 (IP-10) may be a reliable biomarker for immune activity induced by CpG ODNs in pigs.

Activation of foal neutrophils at different ages by CpG oligodeoxynucleotides and Rhodococcus equi

Toll-like receptor 9 (TLR9) activation stimulates protective immune responses against intracellular pathogens by phagocytes, including neutrophils. This study examined TLR9-mediated neutrophil activation in neonatal foals. Unmethylated CpGs, ligands for TLR9, were used to stimulate equine neutrophils, either purified or in contact with other peripheral blood leukocytes. Rhodococcus equi was used as another stimulus in parallel. TLR9 mRNA was constitutively expressed at a similar level in purified equine neutrophils across different ages from birth to adulthood, and expression was not affected by either CpG or R. equi. Purified foal neutrophils were directly sensitive to CpG stimulation, reflected by enhanced reactive oxygen species generation following fMLP stimulation, and by expressing significantly (P<0.05) greater mRNA of IFN-gamma, IL-8, IL-12p35, and significantly (P<0.05) decreased TNF-alpha mRNA. In comparison, purified foal neutrophils stimulated by R. equi showed significantly (P<0.05) increased mRNA production of IL-6, IL-8, IL-23p19, and TNF-alpha. Neutrophils co-cultured with other leukocytes expressed a distinct profile of cytokine mRNA than purified neutrophils in response to CpG stimulation, whereas the profile was very similar following R. equi stimulation irrespective of neutrophil purity. When co-cultured with other leukocytes, foal neutrophils were significantly (P<0.05) activated at birth by B-class CpGs and produced IL-6, IL-8, IL-12p40, and IL-23p19 at similar magnitudes to those at 2 months of age. In foal neutrophils at birth, R. equi significantly (P<0.05) induced all cytokines stimulated by CpGs (except IL-12p40), as well as TNF-alpha. Our results indicate that foal neutrophils were sensitive to CpG or R. equi activation as early as at birth, and that B-class CpGs enhanced foal neutrophil functions in vitro.

Intratracheal synthetic CpG oligodeoxynucleotide causes acute lung injury with systemic inflammatory response

Bacterial genome is characterized by frequent unmethylated cytosine-phosphate-guanine (CpG) motifs. Deleterious effects can occur when synthetic oligodeoxynucleotides (ODN) with unmethylated CpG dinucleotides (CpG-ODN) are administered in a systemic fashion. We aimed to evaluate the effect of intratracheal CpG-ODN on lung inflammation and systemic inflammatory response. C57BL/6J mice received intratracheal administration of CpG-ODN (0.01, 0.1, 1.0, 10, or 100 μM) or control ODN without CpG motif. Bronchoalveolar lavage (BAL) fluid was obtained 3 or 6 h or 1, 2, 7, or 14 days after the instillation and subjected to a differential cell count and cytokine measurement. Lung permeability was evaluated as the BAL fluid-to-plasma ratio of the concentration of human serum albumin that was injected 1 h before euthanasia. Nuclear factor (NF)-κB DNA binding activity was also evaluated in lung homogenates. Intratracheal administration of 10 μM or higher concentration of CpG-ODN induced significant inflammatory cell accumulation into the airspace. The peak accumulation of neutrophils and lymphocytes occurred 1 and 2 days after the CpG-ODN administration, respectively. Lung permeability was increased 1 day after the 10 μM CpG-ODN challenge. CpG-ODN also induced nuclear translocation of NF-κB and upregulation of various inflammatory cytokines in BAL fluid and plasma. Histopathology of the lungs and liver revealed acute lung injury and liver damage with necrosis, respectively. Control ODN without CpG motif did not induce any inflammatory change. Since intratracheal CpG-ODN induced acute lung injury as well as systemic inflammatory response, therapeutic strategies to neutralize bacterial DNA that is released after administration of bactericidal agents should be considered.

Intranasal administration of a detoxified endotoxin vaccine protects mice against heterologous Gram-negative bacterial pneumonia

When given passively or elicited actively, antibodies induced by a detoxified Escherichia coli J5 mutant lipopolysaccharide (J5dLPS)-group B meningococcal outer membrane protein (-OMP) vaccine previously protected animals from lethal sepsis. To assess the use of this vaccine for the treatment of Gram-negative bacillary pneumonia, we vaccinated mice, with or without the adjuvant CpG, by intranasal (i.n.) or intraperitoneal (i.p.) routes of administration. Local and systemic IgG levels were 2-3 logs higher following i.p. immunization compared to i.n. However, i.n. immunization elicited both local and systemic IgA, unlike i.p. administration. The addition of CpG to the vaccine, by either route of administration, elicited greater levels of antibody. Intranasal immunization protected mice against lethal heterologous Gram-negative bacillary pneumonia and post-immunization serum and broncho-alveolar lavage fluid mediated enhanced bacterial killing with peritoneal and alveolar macrophages in vitro. We conclude that further studies on the use of J5dLPS-OMP for the prevention of nosocomial pneumonia are warranted.

Immune Mechanisms and Therapeutic Potential of CpG Oligodeoxynucleotides

Unmethylated CpG motifs in bacterial DNA and synthetic oligodeoxynucleotides activate immune cells that express Toll-like Receptor 9. Activation through this receptor triggers cellular signaling that leads to production of a proinflammatory and a Th1-type, antigen-specific immune response. The immunostimulatory effects of CpG oligodeoxynucleotides confer protection against infectious disease, allergy and cancer in animal models, and clinical trials have been initiated. However, CpG oligodeoxynucleotides may exacerbate disease in some situations. We will review current concepts in the mechanisms of activating Toll-like Receptor 9 with CpG oligodeoxynucleotides and highlight opportunities for using large animal models to better determine the mechanisms of action.