Signaling via pattern recognition receptors NOD2 and TLR2 contributes to immunomodulatory control of lethal pneumovirus infection

Short-Chain Fatty Acid (SCFA) as a Connecting Link between Microbiota and Gut-Lung Axis-A Potential Therapeutic Intervention to Improve Lung Health

The microbiome is an integral part of the human gut, and it plays a crucial role in the development of the immune system and homeostasis. Apart from the gut microbiome, the airway microbial community also forms a distinct and crucial part of the human microbiota. Furthermore, several studies indicate the existence of communication between the gut microbiome and their metabolites with the lung airways, called "gut-lung axis". Perturbations in gut microbiota composition, termed dysbiosis, can have acute and chronic effects on the pathophysiology of lung diseases. Microbes and their metabolites in lung stimulate various innate immune pathways, which modulate the expression of the inflammatory genes in pulmonary leukocytes. For instance, gut microbiota-derived metabolites such as short-chain fatty acids can suppress lung inflammation through the activation of G protein-coupled receptors (free fatty acid receptors) and can also inhibit histone deacetylase, which in turn influences the severity of acute and chronic respiratory diseases. Thus, modulation of the gut microbiome composition through probiotic/prebiotic usage and fecal microbiota transplantation can lead to alterations in lung homeostasis and immunity. The resulting manipulation of immune cells function through microbiota and their key metabolites paves the way for the development of novel therapeutic strategies in improving the lung health of individuals affected with various lung diseases including SARS-CoV-2. This review will shed light upon the mechanistic aspect of immune system programming through gut and lung microbiota and exploration of the relationship between gut-lung microbiome and also highlight the therapeutic potential of gut microbiota-derived metabolites in the management of respiratory diseases.

The Dual Role of the Innate Immune System in the Effectiveness of mRNA Therapeutics

Advances in molecular biology have revolutionized the use of messenger RNA (mRNA) as a therapeutic. The concept of nucleic acid therapy with mRNA originated in 1990 when Wolff et al. reported successful expression of proteins in target organs by direct injection of either plasmid DNA or mRNA. It took decades to bring the transfection efficiency of mRNA closer to that of DNA. The next few decades were dedicated to turning in vitro-transcribed (IVT) mRNA from a promising delivery tool for gene therapy into a full-blown therapeutic modality, which changed the biotech market rapidly. Hundreds of clinical trials are currently underway using mRNA for prophylaxis and therapy of infectious diseases and cancers, in regenerative medicine, and genome editing. The potential of IVT mRNA to induce an innate immune response favors its use for vaccination and immunotherapy. Nonetheless, in non-immunotherapy applications, the intrinsic immunostimulatory activity of mRNA directly hinders the desired therapeutic effect since it can seriously impair the target protein expression. Targeting the same innate immune factors can increase the effectiveness of mRNA therapeutics for some indications and decrease it for others, and vice versa. The review aims to present the innate immunity-related 'barriers' or 'springboards' that may affect the development of immunotherapies and non-immunotherapy applications of mRNA medicines.

Reduced microbial diversity of the nasopharyngeal microbiome in household contacts with latent tuberculosis infection

The upper respiratory tract is an obliged pathway for respiratory pathogens and a healthy microbiota may support the host's mucosal immunity preventing infection. We analyzed the nasopharyngeal microbiome in tuberculosis household contacts (HHCs) and its association with latent tuberculosis infection (TBI). A prospective cohort of HHCs was established and latent TBI status was assessed by serial interferon-γ release assay (IGRA). Nasopharyngeal swabs collected at baseline were processed for 16S rRNA gene sequencing. The 82 participants included in the analysis were classified as: (a) non-TBI [IGRA negative at baseline and follow-up, no active TB (n = 31)], (b) pre-TBI [IGRA negative at baseline but converted to IGRA positive or developed active TB at follow-up (n = 16)], and (c) TBI [IGRA positive at enrollment (n = 35)]. Predominant phyla were Actinobacteriota, Proteobacteria, Firmicutes and Bacteroidota. TBI group had a lower alpha diversity compared to non-TBI (p_adj = 0.04) and pre-TBI (p_adj = 0.04). Only TBI and non-TBI had beta diversity differences (p_adj = 0.035). Core microbiomes' had unique genera, and genus showed differential abundance among groups. HHCs with established latent TBI showed reduced nasopharyngeal microbial diversity with distinctive taxonomical composition. Whether a pre-existing microbiome feature favors, are a consequence, or protects against Mycobacterium tuberculosis needs further investigation.

Lactic Acid Bacteria as Mucosal Immunity Enhancers and Antivirals through Oral Delivery

Mucosal vaccination offer an advantage over systemic inoculation from the immunological viewpoint. The development of an efficient vaccine is now a priority for emerging diseases such as COVID-19, that was declared a pandemic in 2020 and caused millions of deaths globally. Lactic acid bacteria (LAB) especially Lactobacillus are the vital microbiota of the gut, which is observed as having valuable effects on animals’ and human health. LAB produce lactic acid as the major by-product of carbohydrate degradation and play a significant role in innate immunity enhancement. LAB have significant characteristics to mimic pathogen infections and intrinsically possess adjuvant properties to enhance mucosal immunity. Increasing demand and deliberations are being substantially focused on probiotic organisms that can enhance mucosal immunity against viral diseases. LAB can also strengthen their host’s antiviral defense system by producing antiviral peptides, and releasing metabolites that prevent viral infections and adhesion to mucosal surfaces. From the perspectives of “one health” and the use of probiotics, conventional belief has opened up a new horizon on the use of LAB as antivirals. The major interest of this review is to depict the beneficial use of LAB as antivirals and mucosal immunity enhancers against viral diseases.

The role of respiratory microbiota in the protection against viral diseases: respiratory commensal bacteria as next-generation probiotics for COVID-19

On March 11, 2020, the World Health Organization declared a pandemic of coronavirus infectious disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and imposed the biggest public health challenge for our civilization, with unforeseen impacts in the subsequent years. Similar to other respiratory infections, COVID-19 is associated with significant changes in the composition of the upper respiratory tract microbiome. Studies have pointed to a significant reduction of diversity and richness of the respiratory microbiota in COVID-19 patients. Furthermore, it has been suggested that Prevotella, Staphylococcus, and Streptococcus are associated with severe COVID-19 cases, while Dolosigranulum and Corynebacterium are significantly more abundant in asymptomatic subjects or with mild disease. These results have stimulated the search for new microorganisms from the respiratory microbiota with probiotic properties that could alleviate symptoms and even help in the fight against COVID-19. To date, the potential positive effects of probiotics in the context of SARS-CoV-2 infection and COVID-19 pandemics have been extrapolated from studies carried out with other viral pathogens, such as influenza virus and respiratory syncytial virus. However, scientific evidence has started to emerge demonstrating the capacity of immunomodulatory bacteria to beneficially influence the resistance against SARS-CoV-2 infection. Here we review the scientific knowledge regarding the role of the respiratory microbiota in viral infections in general and in the infection caused by SARS-CoV-2 in particular. In addition, the scientific work that supports the use of immunomodulatory probiotic microorganisms as beneficial tools to reduce the severity of respiratory viral infections is also reviewed. In particular, our recent studies that evaluated the role of immunomodulatory Dolosigranulum pigrum strains in the context of SARS-CoV-2 infection are highlighted.

Antiviral Effects and Underlying Mechanisms of Probiotics as Promising Antivirals

Probiotics exert a variety of beneficial effects, including maintaining homeostasis and the balance of intestinal microorganisms, activating the immune system, and regulating immune responses. Due to the beneficial effects of probiotics, a wide range of probiotics have been developed as probiotic agents for animal and human health. Viral diseases cause serious economic losses to the livestock every year and remain a great challenge for animals. Moreover, strategies for the prevention and control of viral diseases are limited. Viruses enter the host through the skin and mucosal surface, in which are colonized by hundreds of millions of microorganisms. The antiviral effects of probiotics have been proved, including modulation of chemical, microbial, physical, and immune barriers through various probiotics, probiotic metabolites, and host signaling pathways. It is of great significance yet far from enough to elucidate the antiviral mechanisms of probiotics. The major interest of this review is to discuss the antiviral effects and underlying mechanisms of probiotics and to provide targets for the development of novel antivirals.

The Beneficial Role of Probiotic Lactobacillus in Respiratory Diseases

Respiratory diseases cause a high incidence and mortality worldwide. As a natural immunobiotic, Lactobacillus has excellent immunomodulatory ability. Administration of some Lactobacillus species can alleviate the symptoms of respiratory diseases such as respiratory tract infections, asthma, lung cancer and cystic fibrosis in animal studies and clinical trials. The beneficial effect of Lactobacillus on the respiratory tract is strain dependent. Moreover, the efficacy of Lactobacillus may be affected by many factors, such as bacteria dose, timing and host background. Here, we summarized the beneficial effect of administered Lactobacillus on common respiratory diseases with a focus on the mechanism and safety of Lactobacillus in regulating respiratory immunity.

Microbiome Modulation as a Novel Strategy to Treat and Prevent Respiratory Infections

Acute and chronic lower airway disease still represent a major cause of morbidity and mortality on a global scale. With the steady rise of multidrug-resistant respiratory pathogens, such as Pseudomonas aeruginosa and Klebsiella pneumoniae, we are rapidly approaching the advent of a post-antibiotic era. In addition, potentially detrimental novel variants of respiratory viruses continuously emerge with the most prominent recent example being severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To this end, alternative preventive and therapeutic intervention strategies will be critical to combat airway infections in the future. Chronic respiratory diseases are associated with alterations in the lung and gut microbiome, which is thought to contribute to disease progression and increased susceptibility to infection with respiratory pathogens. In this review we will focus on how modulating and harnessing the microbiome may pose a novel strategy to prevent and treat pulmonary infections as well as chronic respiratory disease.

Revisiting the Development of Vaccines Against Pathogenic Leptospira: Innovative Approaches, Present Challenges, and Future Perspectives

Human vaccination against leptospirosis has been relatively unsuccessful in clinical applications despite an expressive amount of vaccine candidates has been tested over years of research. Pathogenic Leptospira encompass a great number of serovars, most of which do not cross-react, and there has been a lack of genetic tools for many years. These obstacles have hampered the understanding of the bacteria's biology and, consequently, the identification of an effective antigen. Thus far, many approaches have been used in an attempt to find a cost-effective and broad-spectrum protective antigen(s) against the disease. In this extensive review, we discuss several strategies that have been used to develop an effective vaccine against leptospirosis, starting with Leptospira-inactivated bacterin, proteins identified in the genome sequences of pathogenic Leptospira, including reverse vaccinology, plasmid DNA, live vaccines, chimeric multi-epitope, and toll- and nod-like receptors agonists. This overview should be able to guide scientists working in the field to select potential antigens and to choose the appropriate formulation to administer the candidates.

Differential Expression of Mitosis and Cell Cycle Regulatory Genes during Recovery from an Acute Respiratory Virus Infection

Acute respiratory virus infections can have profound and long-term effects on lung function that persist even after the acute responses have fully resolved. In this study, we examined gene expression by RNA sequencing in the lung tissue of wild-type BALB/c mice that were recovering from a sublethal infection with the pneumonia virus of mice (PVM), a natural rodent pathogen of the same virus family and genus as the human respiratory syncytial virus. We compared these responses to gene expression in PVM-infected mice treated with Lactobacillus plantarum, an immunobiotic agent that limits inflammation and averts the negative clinical sequelae typically observed in response to acute infection with this pathogen. Our findings revealed prominent differential expression of inflammation-associated genes as well as numerous genes and gene families implicated in mitosis and cell-cycle regulation, including cyclins, cyclin-dependent kinases, cell division cycle genes, E2F transcription factors, kinesins, centromere proteins, and aurora kinases, among others. Of particular note was the differential expression of the cell division cycle gene Cdc20b, which was previously identified as critical for the ex vivo differentiation of multi-ciliated cells. Collectively, these findings provided us with substantial insight into post-viral repair processes and broadened our understanding of the mechanisms underlying Lactobacillus-mediated protection.

Network Topology of Biological Aging and Geroscience-Guided Approaches to COVID-19

Aging has emerged as the greatest and most prevalent risk factor for the development of severe COVID-19 infection and death following exposure to the SARS-CoV-2 virus. The presence of multiple co-existing chronic diseases and conditions of aging further enhances this risk. Biological aging not only enhances the risk of chronic diseases, but the presence of such conditions further accelerates varied biological processes or "hallmarks" implicated in aging. Given growing evidence that it is possible to slow the rate of many biological aging processes using pharmacological compounds has led to the proposal that such geroscience-guided interventions may help enhance immune resilience and improve outcomes in the face of SARS-CoV-2 infection. Our review of the literature indicates that most, if not all, hallmarks of aging may contribute to the enhanced COVID-19 vulnerability seen in frail older adults. Moreover, varied biological mechanisms implicated in aging do not function in isolation from each other, and exhibit intricate effects on each other. With all of these considerations in mind, we highlight limitations of current strategies mostly focused on individual single mechanisms, and we propose an approach which is far more multidisciplinary and systems-based emphasizing network topology of biological aging and geroscience-guided approaches to COVID-19.

Persistent Airway Hyperresponsiveness Following Recovery from Infection with Pneumonia Virus of Mice

Respiratory virus infections can have long-term effects on lung function that persist even after the acute responses have resolved. Numerous studies have linked severe early childhood infection with respiratory syncytial virus (RSV) to the development of wheezing and asthma, although the underlying mechanisms connecting these observations remain unclear. Here, we examine airway hyperresponsiveness (AHR) that develops in wild-type mice after recovery from symptomatic but sublethal infection with the natural rodent pathogen, pneumonia virus of mice (PVM). We found that BALB/c mice respond to a limited inoculum of PVM with significant but reversible weight loss accompanied by virus replication, acute inflammation, and neutrophil recruitment to the airways. At day 21 post-inoculation, virus was no longer detected in the airways and the acute inflammatory response had largely resolved. However, and in contrast to most earlier studies using the PVM infection model, all mice survived the initial infection and all went on to develop serum anti-PVM IgG antibodies. Furthermore, using both invasive plethysmography and precision-cut lung slices, we found that these mice exhibited significant airway hyperresponsiveness at day 21 post-inoculation that persisted through day 45. Taken together, our findings extend an important and versatile respiratory virus infection model that can now be used to explore the role of virions and virion clearance as well as virus-induced inflammatory mediators and their signaling pathways in the development and persistence of post-viral AHR and lung dysfunction.

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.

Respiratory Epithelial Cells Respond to Lactobacillus plantarum but Provide No Cross-Protection against Virus-Induced Inflammation

Virus-induced inflammation plays a critical role in determining the clinical outcome of an acute respiratory virus infection. We have shown previously that the administration of immunobiotic Lactobacillus plantarum (Lp) directly to the respiratory tract prevents lethal inflammatory responses to subsequent infection with a mouse respiratory virus pathogen. While Lp-mediated protective responses involve non-redundant contributions of both Toll-like receptor 2 (TLR2) and NOD2, the cellular basis of these findings remains unclear. Here, we address the impact of Lp and its capacity to suppress inflammation in virus-infected respiratory epithelial cells in two cell culture models. We found that both MLE-12 cells and polarized mouse tracheal epithelial cells (mTECs) were susceptible to infection with Influenza A and released proinflammatory cytokines, including CCL2, CCL5, CXCL1, and CXCL10, in response to replicating virus. MLE-12 cells express NOD2 (81 ± 6.3%) and TLR2 (19 ± 4%), respond to Lp, and are TLR2-specific, but not NOD2-specific, biochemical agonists. By contrast, we found that mTECs express NOD2 (81 ± 17%) but minimal TLR2 (0.93 ± 0.58%); nonetheless, mTECs respond to Lp and the TLR2 agonist, Pam2CSK4, but not NOD2 agonists or the bifunctional TLR2-NOD2 agonist, CL-429. Although MLE-12 cells and mTECS were both activated by Lp, little to no cytokine suppression was observed in response to Lp followed by virus infection via a protocol that replicated experimental conditions that were effective in vivo. Further study and a more complex approach may be required to reveal critical factors that suppress virus-induced inflammatory responses.

Phagocyte Escape of Leptospira: The Role of TLRs and NLRs

The spirochetal bacteria Leptospira spp. are causative agents of leptospirosis, a globally neglected and reemerging zoonotic disease. Infection with these pathogens may lead to an acute and potentially fatal disease but also to chronic asymptomatic renal colonization. Both forms of disease demonstrate the ability of leptospires to evade the immune response of their hosts. In this review, we aim first to recapitulate the knowledge and explore the controversial data about the opsonization, recognition, intracellular survival, and killing of leptospires by scavenger cells, including platelets, neutrophils, macrophages, and dendritic cells. Second, we will summarize the known specificities of the recognition or escape of leptospire components (the so-called microbial-associated molecular patterns; MAMPs) by the pattern recognition receptors (PRRs) of the Toll-like and NOD-like families. These PRRs are expressed by phagocytes, and their stimulation by MAMPs triggers pro-inflammatory cytokine and chemokine production and bactericidal responses, such as antimicrobial peptide secretion and reactive oxygen species production. Finally, we will highlight recent studies suggesting that boosting or restoring phagocytic functions by treatments using agonists of the Toll-like or NOD receptors represents a novel prophylactic strategy and describe other potential therapeutic or vaccine strategies to combat leptospirosis.

Identification of potential mRNA panels for severe acute respiratory syndrome coronavirus 2 (COVID-19) diagnosis and treatment using microarray dataset and bioinformatics methods

The goal of the present investigation is to identify the differentially expressed genes (DEGs) between SARS-CoV-2 infected and normal control samples to investigate the molecular mechanisms of infection with SARS-CoV-2. The microarray data of the dataset E-MTAB-8871 were retrieved from the ArrayExpress database. Pathway and Gene Ontology (GO) enrichment study, protein–protein interaction (PPI) network, modules, target gene–miRNA regulatory network, and target gene–TF regulatory network have been performed. Subsequently, the key genes were validated using an analysis of the receiver operating characteristic (ROC) curve. In SARS-CoV-2 infection, a total of 324 DEGs (76 up- and 248 down-regulated genes) were identified and enriched in a number of associated SARS-CoV-2 infection pathways and GO terms. Hub and target genes such as TP53, HRAS, MAPK11, RELA, IKZF3, IFNAR2, SKI, TNFRSF13C, JAK1, TRAF6, KLRF2, CD1A were identified from PPI network, target gene–miRNA regulatory network, and target gene–TF regulatory network. Study of the ROC showed that ten genes (CCL5, IFNAR2, JAK2, MX1, STAT1, BID, CD55, CD80, HAL-B, and HLA-DMA) were substantially involved in SARS-CoV-2 patients. The present investigation identified key genes and pathways that deepen our understanding of the molecular mechanisms of SARS-CoV-2 infection, and could be used for SARS-CoV-2 infection as diagnostic and therapeutic biomarkers.

Alternaria alternata Accelerates Loss of Alveolar Macrophages and Promotes Lethal Influenza A Infection

Chronic inhalation of fungi and fungal components has been linked to the development of respiratory disorders, although their role with respect to the pathogenesis of acute respiratory virus infection remains unclear. Here, we evaluate inflammatory pathology induced by repetitive administration of a filtrate of the ubiquitous fungus, Alternaria alternata, and its impact on susceptibility to infection with influenza A. We showed previously that A. alternata at the nasal mucosae resulted in increased susceptibility to an otherwise sublethal inoculum of influenza A in wild-type mice. Here we demonstrate that A. alternata-induced potentiation of influenza A infection was not dependent on fungal serine protease or ribonuclease activity. Repetitive challenge with A. alternata prior to virus infection resulted proinflammatory cytokines, neutrophil recruitment, and loss of alveolar macrophages to a degree that substantially exceeded that observed in response to influenza A infection alone. Concomitant administration of immunomodulatory Lactobacillus plantarum, a strategy shown previously to limit virus-induced inflammation in the airways, blocked the exaggerated lethal response. These observations promote an improved understanding of severe influenza infection with potential clinical relevance for individuals subjected to continuous exposure to molds and fungi.

Innate immune memory through TLR2 and NOD2 contributes to the control of Leptospira interrogans infection

Leptospira interrogans are pathogenic spirochetes responsible for leptospirosis, a worldwide reemerging zoonosis. Many Leptospira serovars have been described, and prophylaxis using inactivated bacteria provides only short-term serovar-specific protection. Therefore, alternative approaches to limit severe leptospirosis in humans and morbidity in cattle would be welcome. Innate immune cells, including macrophages, play a key role in fighting infection and pathogen clearance. Recently, it has been shown that functional reprograming of innate immune cells through the activation of pattern recognition receptors leads to enhanced nonspecific antimicrobial responses upon a subsequent microbial encounter. This mechanism is known as trained immunity or innate immune memory. We have previously shown that oral treatment with Lactobacillus plantarum confers a beneficial effect against acute leptospirosis. Here, using a macrophage depletion protocol and live imaging in mice, we established the role of peritoneal macrophages in limiting the initial dissemination of leptospires. We further showed that intraperitoneal priming of mice with CL429, a TLR2 and NOD2 agonist known to mimic the modulatory effect of Lactobacillus, alleviated acute leptospiral infection. The CL429 treatment was characterized as a training effect since i.) it was linked to peritoneal macrophages that produced ex vivo more pro-inflammatory cytokines and chemokines against 3 different pathogenic serovars of Leptospira, independently of the presence of B and T cells, ii.) it had systemic effects on splenic cells and bone marrow derived macrophages, and iii.) it was sustained for 3 months. Importantly, trained macrophages produced more nitric oxide, a potent antimicrobial compound, which has not been previously linked to trained immunity. Accordingly, trained macrophages better restrict leptospiral survival. Finally, we could use CL429 to train ex vivo human monocytes that produced more cytokines upon leptospiral stimulation. In conclusion, host-directed treatment using a TLR2/NOD2 agonist could be envisioned as a novel prophylactic strategy against acute leptospirosis.

Critical Adverse Impact of IL-6 in Acute Pneumovirus Infection

Severe respiratory virus infections feature robust local host responses that contribute to disease severity. Immunomodulatory strategies that limit virus-induced inflammation may be of critical importance, notably in the absence of antiviral vaccines. In this study, we examined the role of the pleiotropic cytokine IL-6 in acute infection with pneumonia virus of mice (PVM), a natural rodent pathogen that is related to respiratory syncytial virus and that generates local inflammation as a feature of severe infection. In contrast to Influenza A, PVM is substantially less lethal in IL-6 -/- mice than it is in wild-type, a finding associated with diminished neutrophil recruitment and reduced fluid accumulation in lung tissue. Ly6Chi proinflammatory monocytes are recruited in response to PVM via a CCR2-dependent mechanism, but they are not a major source of IL-6 nor do they contribute to lethal sequelae of infection. By contrast, alveolar macrophages are readily infected with PVM in vivo; ablation of alveolar macrophages results in prolonged survival in association with a reduction in virus-induced IL-6. Finally, as shown previously, administration of immunobiotic Lactobacillus plantarum to the respiratory tracts of PVM-infected mice promoted survival in association with diminished levels of IL-6. We demonstrated in this study that IL-6 suppression is a critical feature of the protective mechanism; PVM-infected IL-6 -/- mice responded to low doses of L. plantarum, and administration of IL-6 overcame L. plantarum-mediated protection in PVM-infected wild-type mice. Taken together, these results connect the actions of IL-6 to PVM pathogenesis and suggest cytokine blockade as a potential therapeutic modality in severe infection.

Toll-like Receptor Agonist Conjugation: A Chemical Perspective

Toll-like receptors (TLRs) are vital elements of the mammalian immune system that function by recognizing pathogen-associated molecular patterns (PAMPs), bridging innate and adaptive immunity. They have become a prominent therapeutic target for the treatment of infectious diseases, cancer, and allergies, with many TLR agonists currently in clinical trials or approved as immunostimulants. Numerous studies have shown that conjugation of TLR agonists to other molecules can beneficially influence their potency, toxicity, pharmacokinetics, or function. The functional properties of TLR agonist conjugates, however, are highly dependent on the ligation strategy employed. Here, we review the chemical structural requirements for effective functional TLR agonist conjugation. In addition, we provide similar analysis for those that have yet to be conjugated. Moreover, we discuss applications of covalent TLR agonist conjugation and their implications for clinical use.

Administration of immunobiotic Lactobacillus plantarum delays but does not prevent lethal pneumovirus infection in Rag1-/- mice

Administration of immunobiotic Lactobacillus plantarum (Lp) directly to the respiratory mucosa promotes cross-protection against lethal pneumovirus infection via B-cell-independent mechanisms. In this study, we examined Lp-mediated cross protection in Rag1^-/- mice which cannot clear virus from lung tissue. Although Lp was initially protective, Rag1^-/- mice ultimately succumbed to a delayed lethal outcome associated with local production of the proinflammatory cytokines CCL1, -2, and -7, granulocyte recruitment, and ongoing virus replication. By contrast, CD8^null mice, which are fully capable of clearing virus, are protected by Lp with no delayed lethal outcome, granulocyte recruitment to the airways, or induction of CCL7. Repeated administration of Lp to virus-infected Rag1^-/- mice had no impact on delayed mortality. Moreover, administration of Lp to the respiratory mucosa resulted in no induction of IFN-α or -β in Rag1^-/- or wild-type mice, and IFN-abR gene deletion had no impact on Lp-mediated protection. Overall, our findings indicate that although Lp administered to the respiratory tract has substantial impact on lethal virus-induced inflammation in situ, endogenous virus clearance mechanisms are needed to promote sustained protection. Our results suggest that a larger understanding of the mechanisms and mediators that limit acute virus-induced inflammation may yield new and useful therapeutic modalities.

The microbiota of the respiratory tract: gatekeeper to respiratory health

The respiratory tract is a complex organ system that is responsible for the exchange of oxygen and carbon dioxide. The human respiratory tract spans from the nostrils to the lung alveoli and is inhabited by niche-specific communities of bacteria. The microbiota of the respiratory tract probably acts as a gatekeeper that provides resistance to colonization by respiratory pathogens. The respiratory microbiota might also be involved in the maturation and maintenance of homeostasis of respiratory physiology and immunity. The ecological and environmental factors that direct the development of microbial communities in the respiratory tract and how these communities affect respiratory health are the focus of current research. Concurrently, the functions of the microbiome of the upper and lower respiratory tract in the physiology of the human host are being studied in detail. In this Review, we will discuss the epidemiological, biological and functional evidence that support the physiological role of the respiratory microbiota in the maintenance of human health.

Silkworm larvae plasma (SLP) assay for detection of bacteria: False positives secondary to inflammation in vivo

The silkworm larvae plasma (SLP) assay has been developed as a means to detect bacterial peptidoglycan as a surrogate for live bacteria. Here, we present results that indicate that generation of melanin by this assay is not fully reliable as a surrogate marker for bacterial count.