Subcutaneous immunization with Streptococcus pneumoniae GAPDH confers effective protection in mice via TLR2 and TLR4

The implication of dendritic cells in lung diseases: Immunological role of toll-like receptor 4

The immune responses play a profound role in the progression of lung lesions in both infectious and non-infectious diseases. Dendritic cells, as the "frontline" immune cells responsible for antigen presentation, set up a bridge between innate and adaptive immunity in the course of these diseases. Among the receptors equipped in dendritic cells, Toll-like receptors are a group of specialized receptors as one type of pattern recognition receptors, capable of sensing environmental signals including invading pathogens and self-antigens. Toll-like receptor 4, a pivotal member of the Toll-like receptor family, was formerly recognized as a receptor sensitive to the outer membrane component lipopolysaccharide derived from Gram-negative bacteria, triggering the subsequent response. Moreover, its other essential roles in immune responses have drawn significant attention in the past decade. A better understanding of the implication of Toll-like receptor 4 in dendritic cells could contribute to the management of pulmonary diseases including pneumonia, pulmonary tuberculosis, asthma, acute lung injury, and lung cancer.

Anchorless Bacterial Moonlighting Metabolic Enzymes Modulate the Immune System and Contribute to Pathogenesis

Moonlighting proteins (MPs), characterized by their ability to perform multiple physiologically unrelated functions without alterations to their primary structures, represent a fascinating class of biomolecules with significant implications for host-pathogen interactions. This Review highlights the emerging importance of metabolic moonlighting proteins (MetMPs) in bacterial pathogenesis, focusing on their non-canonical secretion and unconventional surface anchoring mechanisms. Despite lacking typical signal peptides and anchoring motifs, MetMPs such as acetaldehyde alcohol dehydrogenase (AdhE) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are secreted and localized to the bacterial surface under stress conditions, facilitating host colonization and immune evasion. The secretion of MetMPs, often observed during conditions such as resource scarcity or infection, suggests a complex regulation akin to the overexpression of heat shock proteins in response to environmental stresses. This Review proposes two potential pathways for MetMP secretion: membrane damage-induced permeability and co-transportation with traditionally secreted proteins, highlighting a remarkable bacterial adaptability. Biophysically, surface anchoring of MetMPs is driven by electrostatic interactions, bypassing the need for conventional anchoring sequences. This mechanism is exemplified by the interaction between the bifunctional enzyme AdhE (known as Listeria adhesion protein, LAP) and the internalin B (InlB) in Listeria monocytogenes, which is mediated by charged residues facilitating adhesion to host tissues. Furthermore, MetMPs play critical roles in iron homeostasis, immune modulation, and evasion, underscoring their multifaceted roles in bacterial pathogenicity. The intricate dynamics of MetMP secretion and anchoring underline the need for further research to unravel the molecular mechanisms underpinning these processes, offering potential new targets for therapeutic intervention against bacterial infections.

Nucleic acid sensing Toll-like receptors 3 and 9 play complementary roles in the development of bacteremia after nasal colonization associated with influenza co-infection

Streptococcus pneumoniae can cause mortality in infant, elderly, and immunocompromised individuals owing to invasion of bacteria to the lungs, the brain, and the blood. In building strategies against invasive infections, it is important to achieve greater understanding of how the pneumococci are able to survive in the host. Toll-like receptors (TLRs), critically important components in the innate immune system, have roles in various stages of the development of infectious diseases. Endosomal TLRs recognize nucleic acids of the pathogen, but the impact on the pneumococcal diseases of immune responses from signaling them remains unclear. To investigate their role in nasal colonization and invasive disease with/without influenza co-infection, we established a mouse model of invasive pneumococcal diseases directly developing from nasal colonization. TLR9 KO mice had bacteremia more frequently than wildtype in the pneumococcal mono-infection model, while the occurrence of bacteremia was higher among TLR3 KO mice after infection with influenza in advance of pneumococcal inoculation. All TLR KO strains showed poorer survival than wildtype after the mice had bacteremia. The specific and protective role of TLR3 and TLR9 was shown in developing bacteremia with/without influenza co-infection respectively, and all nucleic sensing TLRs would contribute equally to protecting sepsis after bacteremia.

Subcutaneous Streptococcus dysgalactiae GAPDH vaccine in mice induces a proficient innate immune response

BACKGROUND

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) on the surface of Streptococcus dysgalactiae, coded with gapC, is a glycolytic enzyme that was reported to be a moonlighting protein and virulence factor.

OBJECTIVE

This study assessed GAPDH as a potential immunization candidate protein to prevent streptococcus infections.

METHODS

Mice were vaccinated subcutaneously with recombinant GAPDH and challenged with S. dysgalactiae in vivo. They were then evaluated using histological methods. rGAPDH of mouse bone marrow-derived dendritic cells (BMDCs) was evaluated using immunoblotting, reverse transcription quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay methods.

RESULTS

Vaccination with rGAPDH improved the survival rates and decreased the bacterial burdens in the mammary glands compared to the control group. The mechanism by which rGAPDH vaccination protects against S. dysgalactiae was investigated. In vitro experiments showed that rGAPDH boosted the generation of interleukin-10 and tumor necrosis factor-α. Treatment of BMDCs with TAK-242, a toll-like receptor 4 inhibitor, or C29, a toll-like receptor 2 inhibitor, reduced cytokines substantially, suggesting that rGAPDH may be a potential ligand for both TLR2 and TLR4. Subsequent investigations showed that rGAPDH may activate the phosphorylation of MAPKs and nuclear factor-κB.

CONCLUSIONS

GAPDH is a promising immunization candidate protein for targeting virulence and enhancing immune-mediated protection. Further investigations are warranted to understand the mechanisms underlying the activation of BMDCs by rGAPDH in a TLR2- and TLR4-dependent manner and the regulation of inflammatory cytokines contributing to mastitis pathogenesis.

A Moonlighting Protein Secreted by a Nasal Microbiome Fortifies the Innate Host Defense Against Bacterial and Viral Infections

Evidence suggests that the human respiratory tract, as with the gastrointestinal tract, has evolved to its current state in association with commensal microbes. However, little is known about how the airway microbiome affects the development of airway immune system. Here, we uncover a previously unidentified mode of interaction between host airway immunity and a unique strain (AIT01) of Staphylococcus epidermidis, a predominant species of the nasal microbiome. Intranasal administration of AIT01 increased the population of neutrophils and monocytes in mouse lungs. The recruitment of these immune cells resulted in the protection of the murine host against infection by Pseudomonas aeruginosa, a pathogenic bacterium. Interestingly, an AIT01-secreted protein identified as GAPDH, a well-known bacterial moonlighting protein, mediated this protective effect. Intranasal delivery of the purified GAPDH conferred significant resistance against other Gram-negative pathogens (Klebsiella pneumoniae and Acinetobacter baumannii) and influenza A virus. Our findings demonstrate the potential of a native nasal microbe and its secretory protein to enhance innate immune defense against airway infections. These results offer a promising preventive measure, particularly relevant in the context of global pandemics.

Activation of the toll-like receptor 2 signaling pathway by GAPDH from bacterial strain RD055328

We characterized the membrane vesicle fraction (RD-MV fraction) from bacterial strain RD055328, which is related to members of the genus Companilactobacillus and Lactiplantibacillus plantarum. RD-MVs and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were detected in the RD-MV fraction. Immunoglobulin A (IgA) was produced by Peyer's patch cells following the addition of the RD-MV fraction. In the presence of the RD-MV fraction, RAW264 cells produced the pro-inflammatory cytokine IL-6. Recombinant GAPDH probably induced the production of IL-6 by RAW264 cells via superficial toll-like receptor 2 (TLR2) recognition. A confocal laser scanning microscopy image analysis indicated that RD-MVs and GAPDH were taken up by RAW264 cells. GAPDH wrapped around RAW264 cells. We suggest that GAPDH from strain RD055328 enhanced the production of IgA by acquired immune cells via the production of IL-6 by innate immune cells through TLR2 signal transduction.

Microbial metabolites indole derivatives sensitize mice to D-GalN/LPS induced-acute liver failure via the Tlr2/NF-κB pathway

Introduction

Acute liver failure (ALF) is a clinical condition with many causes, fast progression, and a poor prognosis. Previous research has indicated that microbial factors have a role in ALF, but a clear picture has yet to emerge.

Methods

To investigate the specific involvement of microbial metabolites in ALF development, we pretreated D-GalN/LPS-induced ALF mice with indole derivatives, an influential class of gut microbial metabolites.

Results

Contrary to their typical role as anti-inflammatory agents in the host, indole-3-acetic acid (IAA), indole-3-lactic acid (ILA), and indolepropionic acid (IPA) gavage sensitize mice to D-GalN/LPS-induced-ALF with a rapid rise in serum transaminases and histologic lesion. For a clearer picture, we performed comprehensive analysis for the IAA therapy. IAA markedly amplified inflammatory response and cellular damage. The transcriptome analysis indicated the participation of the TNF-α/NF-κB signaling pathway. The structure of gut microbiota in ileum and the expression of Toll-like receptor 2 (Tlr2) in the liver were also significantly changed.

Discussion

In conclusion, IAA pretreatment can exacerbate D-GalN/LPS-induced ALF via probable Tlr2/NF-κB pathway involvement and ileac dysbiosis characterized by enriched gram-positive genus with potential pathogenesis. Microbial metabolites IAA may aggravate individual susceptibility to D-GalN/LPS-induced ALF. Further investigation of the underlying mechanism is needed, and intervention with indole derivatives and related commensal species should be undertaken with caution.

Immunomodulatory effects of extracellular glyceraldehyde 3-phosphate dehydrogenase of exopolysaccharide-producing Lactiplantibacillus plantarum JCM 1149

Probiotic lactic acid bacteria evoke immunomodulatory effects in the host; however, the reasons for the different effects of various species and strains remain to be elucidated. To clarify the critical immunomodulatory components and impact of exopolysaccharide (EPS) in Lactiplantibacillus plantarum, 11 types of L. plantarum strains were compared for the production of EPS, inflammatory cytokines, interleukin-6 and -12, and the anti-inflammatory cytokine, interleukin-10, from THP-1 differentiated dendritic cells. EPS in the fermented medium correlated with cytokine-inducing activities. L. plantarum JCM 1149, with the highest production of EPS, also induced interleukin-6, -10, and -12 among the 11 tested strains. Notably, the cytokine-producing activities overlapped with the protein fraction in gel filtration chromatography but not with EPS, which has been reported to exert immunomodulatory effects. The 41 kDa protein that coexisted with EPS was purified as a major active component and identified as glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a known moonlighting protein. GAPDH secretion was reduced when EPS synthesis inhibitors were added to the culture medium. RNA sequencing of GAPDH-treated THP-1 cells revealed an up-regulation in the expression of genes involved in transcriptional regulation, cell surface receptor signalling, immune response, and matrix components. Here, we report, to our knowledge for the first time, that the cell surface-associated L. plantarum GAPDH plays a crucial role in cytokine production in THP-1 cells, but EPS with less activity may help GAPDH secretion.

A journey through the Corynebacterium pseudotuberculosis proteome promotes insights into its functional genome

Background

Corynebacterium pseudotuberculosis is a Gram-positive facultative intracellular pathogen and the etiologic agent of illnesses like caseous lymphadenitis in small ruminants, mastitis in dairy cattle, ulcerative lymphangitis in equines, and oedematous skin disease in buffalos. With the growing advance in high-throughput technologies, genomic studies have been carried out to explore the molecular basis of its virulence and pathogenicity. However, data large-scale functional genomics studies are necessary to complement genomics data and better understating the molecular basis of a given organism. Here we summarize, MS-based proteomics techniques and bioinformatics tools incorporated in genomic functional studies of C. pseudotuberculosis to discover the different patterns of protein modulation under distinct environmental conditions, and antigenic and drugs targets.

Methodology

In this study we performed an extensive search in Web of Science of original and relevant articles related to methods, strategy, technology, approaches, and bioinformatics tools focused on the functional study of the genome of C. pseudotuberculosis at the protein level.

Results

Here, we highlight the use of proteomics for understating several aspects of the physiology and pathogenesis of C. pseudotuberculosis at the protein level. The implementation and use of protocols, strategies, and proteomics approach to characterize the different subcellular fractions of the proteome of this pathogen. In addition, we have discussed the immunoproteomics, immunoinformatics and genetic tools employed to identify targets for immunoassays, drugs, and vaccines against C. pseudotuberculosis infection.

Conclusion

In this review, we showed that the combination of proteomics and bioinformatics studies is a suitable strategy to elucidate the functional aspects of the C. pseudotuberculosis genome. Together, all information generated from these proteomics studies allowed expanding our knowledge about factors related to the pathophysiology of this pathogen.

Enhanced immune effects and protection conferred by simultaneously targeting GAPDH, SeM, and EAG of S. equi via TLR4

Strangles, which is caused by Streptococcus equi subspecies equi, is one of the most prevalent equine infectious diseases and poses heavy economic losses worldwide. Although various vaccines have been used for decades, they seemed to be sub-optimal to demonstrate effective protection, and the antigen component of vaccines against S. equi remains to be optimized. In the present study, three target antigens (M-like protein, α2-macroglobulin and IgG-binding protein, and glyceraldehyde-3-phosphate dehydrogenase) were selected and expressed. Mice were immunized and challenged, and their immune response and efficacy were evaluated. The results revealed that this optimized multi-antigen treatment elicited a high expression level of T-cell receptor, major histocompatibility complex I, toll-like receptor TLR-4, and increased specific antibody. In addition, the challenge experiment showed an evidently improved protection efficacy. The present work demonstrated that these three proteins might be used as a promising multicomponent subunit vaccine candidate against S. equi infection.

Streptococcus pneumoniae PepO promotes host anti-infection defense via autophagy in a Toll-like receptor 2/4 dependent manner

Macrophage is essential for host anti-bacterial defense by directly eliminating invading microbes and inducing a series of immune reactions. Here we identified a Streptococcus pneumoniae protein, PepO, as a TLR2/TLR4 bi-ligand. We found that PepO enhances macrophage unspecific phagocytosis and bactericidal activity, which is related to the induction of autophagy in macrophage, for the inhibition of autophagy significantly decreased the phagocytosis and bactericidal activity of PepO-treated macrophage. We confirmed that these effects of PepO are dependent on interacting with both TLR2 and TLR4. The tlr2 or tlr4 deficiency partially abolished the effect of PepO while tlr2/tlr4 deficiency abolished it completely. In vivo study demonstrated that PepO reduced the bacteria load in WT mice significantly, while the depletion of macrophage or tlr2/tlr4 deficiency abrogated the effect of PepO. Our findings suggested the therapeutic potential of PepO and provided experimental evidence for immunotherapy against infectious disease.

Optimized GAPDH-truncated immunogen of Streptococcus equi elicits an enhanced immune response and provides effective protection in a mouse model

Strangles is an acute and frequently diagnosed infectious disease caused by Streptococcus equi subsp. equi. Infection with this pathogen can cause grave losses to the equine industry. The present work investigates glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an important surface-localized virulence factor of S. equi, to determine whether it could be developed into an efficacious and suitable subunit vaccine against strangles. Two different recombinant fragments of S. equi GAPDH, namely, GAPDH-L and GAPDH-S, were constructed and expressed. Further, the antigenicity and immunogenicity of these two recombinant proteins were compared and evaluated in a mouse model. Our results revealed that immune responses were efficiently induced by the proteins in immunized mice. Remarkably, higher survival rates and significantly lower bacterial loads in the lung, liver, kidney, and spleen were observed in the GAPDH-S group compared with the GAPDH-L group after challenge with S. equi. High levels of specific antibodies, elevated antibody titers, and increased proportions of CD8 + T cells further indicated that GAPDH-S elicited better humoral and cellular immune responses than GAPDH-L. Furthermore, the induction of TCR, TLR-2, TLR-3, and TLR-4 significantly increased in the GAPDH-S group compared with those in the GAPDH-L and negative control groups. In summary, our results indicate that the optimized recombinant protein GAPDH-S is a promising candidate construct that may be further developed into a multivalent subunit vaccine for strangles.

Diverse Localization and Protein Binding Abilities of Glyceraldehyde-3-Phosphate Dehydrogenase in Pathogenic Bacteria: The Key to its Multifunctionality?

Bacterial proteins exhibiting two or more unrelated functions, referred to as moonlighting proteins, are suggested to contribute to full virulence manifestation in pathogens. An expanding number of published studies have revealed the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to be a multitasking protein with virulence impact in a number of pathogenic bacteria. This protein can be detected on the bacterial surface or outside the bacterial cell, where it interacts with host proteins. In this way, GAPDH is able to modulate various pathogenic processes. Moreover, it has been shown to be involved in non-enzymatic processes inside the bacterial cell. In this mini review, we summarize main findings concerning the multiple localization and protein interactions of GAPDH derived from bacterial pathogens of humans. We also briefly discuss problems associated with using GAPDH as a vaccine antigen and endeavor to inspire further research to fill gaps in the existing knowledge.

Streptococcus pneumoniae aminopeptidase N contributes to bacterial virulence and elicits a strong innate immune response through MAPK and PI3K/AKT signaling

Streptococcus pneumoniae is a Gram-positive pathogen with high morbidity and mortality globally but some of its pathogenesis remains unknown. Previous research has provided evidence that aminopeptidase N (PepN) is most likely a virulence factor of S. pneumoniae. However, its role in S. pneumoniae virulence and its interaction with the host remains to be confirmed. We generated a pepN gene deficient mutant strain and found that its virulence for mice was significantly attenuated as were in vitro adhesion and invasion of host cells. The PepN protein could induce a strong innate immune response in vivo and in vitro and induced secretion of IL-6 and TNF-α by primary peritoneal macrophages via the rapid phosphorylation of MAPK and PI3K/AKT signaling pathways and this was confirmed using specific pathway inhibitors. In conclusion, PepN is a novel virulence factor that is essential for the virulence of S. pneumoniae and induces host innate immunity via MAPK and PI3K/AKT signaling.

Protection against fatal pneumonia through mucosal and subcutaneous immunization with the pneumococcal SP0148 protein

Streptococcus pneumoniae infection is associated with very high morbidity and mortality throughout the world. Vaccines are an effective measure for the reduction of S. pneumoniae infection. In particular, protein vaccines are attracting increasing attention because of their good immunogenicity and wide coverage of serotypes. Therefore, identifying effective protein vaccine targets is important for protein vaccine development. SP0148 is a promising protein vaccine target for S. pneumoniae and is capable of reducing S. pneumoniae colonization in the nasopharynx of mice through the IL-17A pathway. However, the protective effects of SP0148 in fatal pneumococcal infection have not been evaluated. This study used subcutaneous and nasal immunization routes to systematically evaluate the protective effects of the SP0148 protein in fatal pneumococcal infection. Subcutaneous and nasal mucosal immunization with recombinant SP0148 protein produced effective immune protection against infection with a lethal dose of S. pneumoniae and significantly prolonged survival time and increased the survival rate of mice. Furthermore, nasal immunization with SP0148 induced mouse splenocytes to secrete high levels of the cytokines IFN-γ and IL-17A. Both recombinant SP0148 protein and its antiserum inhibited the adhesion of S.pneumoniae D39 to A549 human lung epithelial cells in a dose-dependent manner. In summary, SP0148 induced mice to produce protective immune responses to fatal S. pneumoniae infection, and our results could contribute to the accumulating data on the use of SP0148 protein vaccines.

TLR4 deficiency reduces pulmonary resistance to Streptococcus pneumoniae in gut microbiota-disrupted mice

Streptococcus pneumoniae is a clinically important pathogen responsible for significant morbidity and mortality worldwide. Disruption of the host gut microbiota by antibiotics reduces the pulmonary resistance to S. pneumoniae. The aim of our study was to determine the potential role of TLR4 in the reduced pulmonary resistance to S. pneumoniae following gut microbiota disruption. Wild-type and TLR4-deficient mice were given broad-spectrum antibiotics for 3 weeks by oral gavage to disrupt the gut microbiota, and subsequently inoculated intra-nasally with S. pneumoniae. The extent of the decline in pulmonary resistance in both animal groups was evaluated in terms of the overall survival and pulmonary bacterial clearance. Both survival and pulmonary clearance of S. pneumoniae were lower in the TLR4-deficient mice with disrupted gut microbiota, compared to their intestinally healthy counterparts after pneumococcal infection. However, the degree of decline was much lower in the TLR4-deficient mice compared to the wild-type mice. Our findings indicate that impaired TLR4 function might be the basis of the reduced pulmonary resistance to S. pneumoniae caused by gut microbiota disruption.

Expression of Toll-Like Receptor 2 by Dendritic Cells Is Essential for the DnaJ-ΔA146Ply-Mediated Th1 Immune Response against Streptococcus pneumoniae

The fusion protein DnaJ-ΔA146Ply could induce cross-protective immunity against pneumococcal infection via mucosal and subcutaneous immunization in mice in the absence of additional adjuvants. DnaJ and Ply are both Toll-like receptor 4 (TLR4) but not TLR2 ligands. However, we found that TLR2^-/- mice immunized subcutaneously with DnaJ-ΔA146Ply showed significantly lower survival rates and higher bacterial loads in nasal washes than did wild-type (WT) mice after being challenged with pneumococcal strain D39 or 19F. The gamma interferon (IFN-γ) level in splenocytes decreased in TLR2^-/- mice, indicating that Th1 immunity elicited by DnaJ-ΔA146Ply was impaired in these mice. We explored the mechanism of protective immunity conferred by DnaJ-ΔA146Ply and the role of TLR2 in this process. DnaJ-ΔA146Ply effectively promoted dendritic cell (DC) maturation via TLR4 but not the TLR2 signaling pathway. In a DnaJ-ΔA146Ply-treated DC and naive CD4⁺ T cell coculture system, the deficiency of TLR2 in DCs resulted in a significant decline of IFN-γ production and Th1 subset differentiation. The same effect was observed in adoptive-transfer experiments. In addition, TLR2^-/- DCs showed remarkably lower levels of the Th1-polarizing cytokine IL-12p70 than did WT DCs, suggesting that TLR2 was indispensable for DnaJ-ΔA146Ply-induced IL-12 production and Th1 proliferation. Thus, our findings illustrate that dendritic cell expression of TLR2 is essential for optimal Th1 immune response against pneumococci in mice immunized subcutaneously with DnaJ-ΔA146Ply.