IL17-Producing γδ T Cells May Enhance Humoral Immunity during Pulmonary Pseudomonas aeruginosa Infection in Mice

Immunogenicity and reactogenicity of inactivated SARS-CoV-2 vaccines in healthy adults

Introduction

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly pathogenic to humans and has caused the ongoing coronavirus disease 2019 (COVID-19) pandemic. Vaccines are one of the efficient ways to prevent the viral infection. After COVID-19 vaccination, the monitoring of the dynamic change in neutralizing antibodies is necessary to determine booster requirements.

Methods

We estimated the effectiveness of the inactivated vaccines by monitoring dynamic SARS-CoV-2 neutralizing antibodies for over 2 years. Additionally, we also investigated the activation of T lymphocytes (CD3+ T cells) after three doses of the inactivated vaccine.

Result

The results showed that the rate of reduction of SARS-CoV-2 neutralizing antibody levels gradually showed after each booster dose. The IgG/IgM level at 9 months after the third vaccination were significantly higher than those at 6 months after the second dose (p<0.0001). The expression of CD25+T cell in 18-35 age group was significantly higher than that in the other groups. Nine months after the third dose (the time of last blood sample collection), the expression of CD25+T cell in the 18-35 age group was significantly higher than that at 6 months after the second dose. CD25+T cell in the 18-35 years old group was significantly higher than 6 months after the second vaccination.

Conclusion

CD25, a late activation marker of lymphocytes and high-activity memory T cell subgroup, exhibited higher levels at the later stages after vaccination. COVID-19 booster vaccination in older adults and regular testing of SARS-CoV-2 neutralizing antibodies are recommended. Booster doses should be administered if the antibody level falls below the 30% inhibition rate.

Inulin Prebiotic Protects against Lethal Pseudomonas aeruginosa Acute Infection via γδ T Cell Activation

Pseudomonas aeruginosa (P. aeruginosa) causes harmful lung infections, especially in immunocompromised patients. The immune system and Interleukin (IL)-17-producing γδ T cells (γδ T) are critical in controlling these infections in mice. The gut microbiota modulates host immunity in both cancer and infection contexts. Nutritional intervention is a powerful means of modulating both microbiota composition and functions, and subsequently the host's immune status. We have recently shown that inulin prebiotic supplementation triggers systemic γδ T activation in a cancer context. We hypothesized that prophylactic supplementation with inulin might protect mice from lethal P. aeruginosa acute lung infection in a γδ T-dependent manner. C57Bl/6 mice were supplemented with inulin for 15 days before the lethal P. aeruginosa lung infection, administered intranasally. We demonstrate that prophylactic inulin supplementation triggers a higher proportion of γδ T in the blood, accompanied by a higher infiltration of IL-17-producing γδ T within the lungs, and protects 33% of infected mice from death. This observation relies on γδ T, as in vivo γδ TcR blocking using a monoclonal antibody completely abrogates inulin-mediated protection. Overall, our data indicate that inulin supplementation triggers systemic γδ T activation, and could help resolve lung P. aeruginosa infections. Moreover, our data suggest that nutritional intervention might be a powerful way to prevent/reduce infection-related mortality, by reinforcing the microbiota-dependent immune system.

Mucosal administration of anti-bacterial antibodies provide long-term cross-protection against Pseudomonas aeruginosa respiratory infection

Bacterial respiratory infections, either acute or chronic, are major threats to human health. Direct mucosal administration, through the airways, of therapeutic antibodies (Abs) offers a tremendous opportunity to benefit patients with respiratory infections. The mode of action of anti-infective Abs relies on pathogen neutralization and crystallizable fragment (Fc)-mediated recruitment of immune effectors to facilitate their elimination. Using a mouse model of acute pneumonia induced by Pseudomonas aeruginosa, we depicted the immunomodulatory mode of action of a neutralizing anti-bacterial Abs. Beyond the rapid and efficient containment of the primary infection, the Abs delivered through the airways harnessed genuine innate and adaptive immune responses to provide long-term protection, preventing secondary bacterial infection. In vitro antigen-presenting cells stimulation assay, as well as in vivo bacterial challenges and serum transfer experiments indicate an essential contribution of immune complexes with the Abs and pathogen in the induction of the sustained and protective anti-bacterial humoral response. Interestingly, the long-lasting response protected partially against secondary infections with heterologous P. aeruginosa strains. Overall, our findings suggest that Abs delivered mucosally promotes bacteria neutralization and provides protection against secondary infection. This opens novel perspectives for the development of anti-infective Abs delivered to the lung mucosa, to treat respiratory infections.

The function of γδ T cells in humoral immune responses

PURPOSE

The purpose of this review is to discuss the role of γδ T cells played in humoral immune responses.

BACKGROUND

The γδ T cell receptor (γδ TCR) recognizes antigens, including haptens and proteins, in an MHC-independent manner. The recognition of these antigens by γδ TCRs crosses antigen recognition by the B cell receptors (BCRs), suggesting that γδ T cells may be involved in the process of antigen recognition and activation of B cells. However, the role of γδ T cells in humoral immune responses is still less clear.

METHODS

The kinds of literature about the γδ T cell-B cell interaction were searched on PubMed with search terms, such as γδ T cells, antibody, B cell responses, antigen recognition, and infection.

RESULTS

Accumulating evidence indicates that γδ T cells, independent of αβ T cells, participate in multiple steps of humoral immunity, including B cell maturation, activation and differentiation, antibody production and class switching. Mechanically, γδ T cells affect B cell function by directly interacting with B cells, secreting cytokines, or modulating αβ T cells.

CONCLUSION

In this review, we summarize current knowledge on how γδ T cells take part in the humoral immune response, which may assist future vaccine design.

Immune responses to bacterial lung infections and their implications for vaccination

The pulmonary immune system plays a vital role in protecting the delicate structures of gaseous exchange against invasion from bacterial pathogens. With antimicrobial resistance becoming an increasing concern, finding novel strategies to develop vaccines against bacterial lung diseases remains a top priority. In order to do so, a continued expansion of our understanding of the pulmonary immune response is warranted. Whilst some aspects are well characterised, emerging paradigms such as the importance of innate cells and inducible immune structures in mediating protection provide avenues of potential to rethink our approach to vaccine development. In this review, we aim to provide a broad overview of both the innate and adaptive immune mechanisms in place to protect the pulmonary tissue from invading bacterial organisms. We use specific examples from several infection models and human studies to depict the varying functions of the pulmonary immune system that may be manipulated in future vaccine development. Particular emphasis has been placed on emerging themes that are less reviewed and underappreciated in vaccine development studies.

Understanding Pseudomonas aeruginosa-Host Interactions: The Ongoing Quest for an Efficacious Vaccine

Pseudomonas aeruginosa is a leading cause of chronic respiratory infections in people with cystic fibrosis (CF), bronchiectasis or chronic obstructive pulmonary disease (COPD), and acute infections in immunocompromised individuals. The adaptability of this opportunistic pathogen has hampered the development of antimicrobial therapies, and consequently, it remains a major threat to public health. Due to its antimicrobial resistance, vaccines represent an alternative strategy to tackle the pathogen, yet despite over 50 years of research on anti-Pseudomonas vaccines, no vaccine has been licensed. Nevertheless, there have been many advances in this field, including a better understanding of the host immune response and the biology of P. aeruginosa. Multiple antigens and adjuvants have been investigated with varying results. Although the most effective protective response remains to be established, it is clear that a polarised Th2 response is sub-optimal, and a mixed Th1/Th2 or Th1/Th17 response appears beneficial. This comprehensive review collates the current understanding of the complexities of P. aeruginosa-host interactions and its implication in vaccine design, with a view to understanding the current state of Pseudomonal vaccine development and the direction of future efforts. It highlights the importance of the incorporation of appropriate adjuvants to the protective antigen to yield optimal protection.

IL-17C Protects Nasal Epithelium from Pseudomonas aeruginosa Infection

IL-17 family cytokines are directly involved in host immune responses and the critical mediators for host defense against infection or inflammation. IL-17C is highly expressed in respiratory epithelium and is induced after acute bacterial lung infection. However, the definite function of IL-17C induced by Pseudomonas aeruginosa (PAO1 strain) is not fully understood, and our study was designed to demonstrate IL-17C-induced immune response against PAO1 infection in nasal epithelium. Passage-2 normal human nasal epithelial (NHNE) cells were infected with PAO1 and the relationship between IL-17C-related immune responses and the iron absorption of PAO1, depending on inoculation of recombinant human IL-17C (rhIL-17C), was assessed by measuring the siderophore activity of PAO1. Microarray data showed that IL-17C expression increased 34.7 times at 8 hours postinfection (hpi) in NHNE cells, and IL-17C mRNA levels increased until 48 hpi. The PAO1 colonies significantly increased from 8 hpi in NHNE cells, and siderophore activity of PAO1 was enhanced in the supernatants of PAO1-infected NHNE cells. Interestingly, PAO1 colonies were reduced in PAO1-infected NHNE cells treated with rhIL-17C, and supernatants from NHNE cells treated with rhIL-17C also exhibited decreased PAO1 colonies. We found that the siderophore activity of PAO1 was significantly reduced in the supernatants of NHNE cells treated with rhIL-17C where LCN2 expression was highly elevated. Our findings indicate that IL-17C mediates an antibacterial effect against PAO1 by inhibiting siderophore activity in nasal epithelium. We propose that IL-17C might be an efficient mediator to suppress PAO1 infection through disturbing iron absorption of PAO1 in nasal epithelium.

A live auxotrophic vaccine confers mucosal immunity and protection against lethal pneumonia caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading causes of nosocomial pneumonia and its associated mortality. Moreover, extensively drug-resistant high-risk clones are globally widespread, presenting a major challenge to the healthcare systems. Despite this, no vaccine is available against this high-concerning pathogen. Here we tested immunogenicity and protective efficacy of an experimental live vaccine against P. aeruginosa pneumonia, consisting of an auxotrophic strain which lacks the key enzyme involved in D-glutamate biosynthesis, a structural component of the bacterial cell wall. As the amounts of free D-glutamate in vivo are trace substances in most cases, blockage of the cell wall synthesis occurs, compromising the growth of this strain, but not its immunogenic properties. Indeed, when delivered intranasally, this vaccine stimulated production of systemic and mucosal antibodies, induced effector memory, central memory and IL-17A-producing CD4⁺ T cells, and recruited neutrophils and mononuclear phagocytes into the airway mucosa. A significant improvement in mice survival after lung infection caused by ExoU-producing PAO1 and PA14 strains was observed. Nearly one third of the mice infected with the XDR high-risk clone ST235 were also protected. These findings highlight the potential of this vaccine for the control of acute pneumonia caused by this bacterial pathogen.

Pseudomonas aeruginosa is an opportunistic bacterium and one of the most common causes of healthcare-associated diseases, including acute pneumonia, causing high mortality within immunocompromised hosts. Most of these infections are strikingly difficult to treat using conventional antibiotic therapies, since this microorganism displays high intrinsic resistance to a wide range of antibiotics. Moreover, to date, no vaccine is available for prevention. Here we used a mutated bacterial strain, which is unable to replicate in vivo and to cause disease, as a live vaccine against acute pneumonia caused by this pathogen. When applied intranasally, this vaccine induced immunity both at local and distant body sites, activating immune cells which were recruited into the airway mucosa. This evoked immune response reduced the number of non-surviving mice after infection with two cytotoxic P. aeruginosa strains causing acute lung infection. Some protection was also observed against an internationally disseminated cytotoxic strain. These data indicate that this is a promising vaccine candidate against P. aeruginosa-pneumonia.

Mechanisms and Targeted Therapies for Pseudomonas aeruginosa Lung Infection

Pseudomonas aeruginosa is a complex gram-negative facultative anaerobe replete with a variety of arsenals to activate, modify, and destroy host defense mechanisms. The microbe is a common cause of nosocomial infections and an antibiotic-resistant priority pathogen. In the lung, P. aeruginosa disrupts upper and lower airway homeostasis by damaging the epithelium and evading innate and adaptive immune responses. The biology of these interactions is essential to understand P. aeruginosa pathogenesis. P. aeruginosa interacts directly with host cells via flagella, pili, lipoproteins, lipopolysaccharides, and the type III secretion system localized in the outer membrane. P. aeruginosa quorum-sensing molecules regulate the release of soluble factors that enhance the spread of infection. These characteristics of P. aeruginosa differentially affect lung epithelial, innate, and adaptive immune cells involved in the production of mediators and the recruitment of additional immune cell subsets. Pathogen interactions with individual host cells and in the context of host acute lung infection are discussed to reveal pathways that may be targeted therapeutically.

Bacterial pathogenesis and interleukin-17: interconnecting mechanisms of immune regulation, host genetics, and microbial virulence that influence severity of infection

Interleukin-17 (IL-17) is a pro-inflammatory cytokine involved in the control of many different disorders, including autoimmune, oncogenic, and diverse infectious diseases. In the context of infectious diseases, IL-17 protects the host against various classes of microorganisms but, intriguingly, can also exacerbate the severity of some infections. The regulation of IL-17 expression stems, in part, from the activity of Interleukin-23 (IL-23), which drives the maturation of different classes of IL-17-producing cells that can alter the course of infection. In this review, we analyze IL-17/IL-23 signalling in bacterial infection, and examine the interconnecting mechanisms that link immune regulation, host genetics, and microbial virulence in the context of bacterial pathogenesis. We consider the roles of IL-17 in both acute and chronic bacterial infections, with a focus on mouse models of human bacterial disease that involve infection of mucosal surfaces in the lungs, urogenital, and gastrointestinal tracts. Polymorphisms in IL-17-encoding genes in humans, which have been associated with heightened host susceptibility to some bacterial pathogens, are discussed. Finally, we examine the implications of IL-17 biology in infectious diseases for the development of novel therapeutic strategies targeted at preventing bacterial infection.

Immunization with Bivalent Flagellin Protects Mice against Fatal Pseudomonas aeruginosa Pneumonia

Pseudomonas aeruginosa lung infections present a major challenge to healthcare systems worldwide because they are commonly associated with high morbidity and mortality. Here, we demonstrate the protective efficacy of type a and b flagellins (bivalent flagellin) against acute fatal pneumonia in mice. Mice immunized intranasally with a bivalent flagellin vaccine were challenged by different flagellated strains of P. aeruginosa in an acute pneumonia model. Besides the protective effect of the vaccine, we further measured the host innate and cellular immunity responses. The immunized mice in our study were protected against both strains. Remarkably, active immunization with type a or b flagellin significantly improved survival of mice against heterologous strain compared to flagellin a or b antisera. We also showed that after an intranasal challenge by P. aeruginosa strain, neutrophils are recruited to the airways of vaccinated mice, and that the bivalent flagellin vaccine was proved to be protective by the generated CD4⁺IL-17⁺ Th17 cells. In conclusion, bivalent flagellin vaccine can confer protection against different strains of P. aeruginosa in an acute pneumonia mouse model by eliciting effective cellular and humoral immune responses, including increased IL-17 production and improved opsonophagocytic killing.