The Role of Neutrophils in the Induction of Specific Th1 and Th17 during Vaccination against Tuberculosis

Infection Risk and Vaccination in the Management of Psoriasis: Considerations for Biologic Therapy

This narrative review examines critical considerations for biologic treatment in psoriasis patients, with a focus on infection risks, providing current recommendations and practical considerations for prevention, including vaccination, screening, and management strategies. Since type I (Th1) inflammation and type III (Th17) inflammation protect against intracellular and extracellular infections, respectively, it is logical that biologic treatments blocking these pathways may be associated with an increased risk of infection. It has been proven that TNF inhibitors are associated with an increased risk of latent tuberculosis (LTBI) and hepatitis B virus reactivation. However, not all biologics exert the same immunosuppressive effect, as IL-17 and IL-23 inhibitors may be associated with a lower risk of infection. In general, pre-treatment screening for reactivable infectious diseases is advised for all patients initiating biologic therapy. Vaccination schedules for patients with psoriasis under biologic treatment should mirror those of the general population, including annual influenza and COVID-19 vaccines. Live-attenuated vaccines are generally advised against in patients undergoing biologic treatment. However, some live-attenuated vaccines may be safely administered under specific circumstances with IL-17 or IL-23 inhibitors. Current guidelines and recommendations on this topic were initially designed for TNF inhibitors and later extrapolated to other classes of biologic agents. Thus, they should be revised to better align with the specific pathogenic mechanisms of drugs and clinical evidence, emphasizing individualized treatment approaches.

Efficacy and prognostic value of peripheral blood CD4+ T cells and serum IL-6 and IL-8 in tuberculous meningitis

Objective

To investigate the value of peripheral blood clusters of differentiation 4 (CD4+) T-lymphocyte (T cells) count and serum interleukin-6 (IL-6) and interleukin-8 (IL-8) in the treatment and prognosis of tuberculous meningitis (TBM).

Methods

Sixty-five patients with TBM were prospectively included in the observation group. Sixty-five patients with pulmonary TB and a group of 65 healthy individuals served as the control groups. The differences in peripheral blood CD4+ T-cell count, serum IL-6, and IL-8 levels were compared, and changes in these indices after anti-TB treatment in the observation group were analysed. The observation group was divided into effective and ineffective groups based on their response after 24 weeks of anti-TB treatment. The study also evaluated the influence of peripheral blood CD4+ T-cell count, serum IL-6, and IL-8 levels on the adverse prognosis of TBM during anti-TB treatment.

Results

Before treatment, the CD4+ T-cell count in the peripheral blood of the observation group was lower than in both the control and healthy groups, and serum IL-6 and IL-8 levels were higher than in the control group (P < 0.001). After 24 weeks of anti-TB treatment, the CD4+ T-cell count in the peripheral blood of the observation group increased, whereas the levels of IL-6 and IL-8 decreased significantly (P < 0.001). The levels of CD4+ T cells and IL-6 in the peripheral blood of patients before treatment were identified as independent factors influencing the efficacy of anti-TB treatment (odds ratio [OR] = 0.989, 95 % confidence interval [CI]: 0.980-0.997; OR = 1.010, 95 % CI: 1.003-1.017).

Conclusion

In patients with TBM, the CD4+ T-cell count in the peripheral blood is decreased, whereas serum IL-6 and IL-8 are increased. The combination of CD4+ T cells and IL-8 shows a degree of predictive value for the prognosis of anti-TB treatment.

Detailed phenotyping reveals diverse and highly skewed neutrophil subsets in both the blood and airways during active tuberculosis infection

Introduction

Neutrophils play a complex and important role in the immunopathology of TB. Data suggest they are protective during early infection but become a main driver of immunopathology if infection progresses to active disease. Neutrophils are now recognized to exist in functionally diverse states, but little work has been done on how neutrophil states or subsets are skewed in TB disease.

Methods

To address this, we carried out comprehensive phenotyping by flow cytometry of neutrophils in the blood and airways of individuals with active pulmonary TB with and without HIV co-infection recruited in Durban, South Africa.

Results

Active TB was associated with a profound skewing of neutrophils in the blood toward phenotypes associated with activation and apoptosis, reduced phagocytosis, reverse transmigration, and immune regulation. This skewing was also apparently in airway neutrophils, particularly the regulatory subsets expressing PDL-1 and LOX-1. HIV co-infection did not impact neutrophil subsets in the blood but was associated with a phenotypic change in the airways and a reduction in key neutrophil functional proteins cathelicidin and arginase 1.

Discussion

Active TB is associated with profound skewing of blood and airway neutrophils and suggests multiple mechanisms by which neutrophils may exacerbate the immunopathology of TB. These data indicate potential avenues for reducing neutrophil-mediated lung pathology at the point of diagnosis.

No Evidence of Neutrophil Response Modulation in Goats after Immunization against Paratuberculosis with a Heat-Inactivated Vaccine

Neutrophils are believed to play a role in the initial stages of paratuberculosis, and it has recently been demonstrated that vaccination can modulate their function via priming or through epigenetic and metabolic reprogramming (training). Modulation of the neutrophil response against Mycobacterium avium subspecies paratuberculosis (Map) through vaccination has been demonstrated in a rabbit model but not in ruminants. Therefore, in the present work, the effect of vaccination on the response of caprine neutrophils against Map was studied. Neutrophils were isolated from non-vaccinated (n = 7) and Gudair®-vaccinated goat kids (n = 7), before vaccination and 30 days post-vaccination. Then, several neutrophil functions were quantified ex vivo: cell-free and anchored neutrophil extracellular trap (NET) release, phagocytosis, and the differential expression of several cytokines and TLR2. The induction of cell-free NETosis and TLR2 expression by Map is reported for the first time. However, vaccination showed no significant effect on any of the functions studied. This suggests that the protection conferred by Gudair® vaccination is based on mechanisms that are independent of the neutrophil function modulation. Further research into the impact of alternative vaccination strategies or the paratuberculosis infection stage on ruminant neutrophil function could provide valuable insights into its role in paratuberculosis.

Silicone implant surface microtopography modulates inflammation and tissue repair in capsular fibrosis

Excessive fibrous capsule formation around silicone mammary implants (SMI) involves immune reactions to silicone. Capsular fibrosis, a common SMI complication linked to host responses, worsens with specific implant topographies. Our study with 10 patients investigated intra- and inter-individually, reduced surface roughness effects on disease progression, wound responses, chronic inflammation, and capsular composition. The results illuminate the significant impact of surface roughness on acute inflammatory responses, fibrinogen accumulation, and the subsequent fibrotic cascade. The reduction of surface roughness to an average roughness of 4 μm emerges as a promising approach for mitigating detrimental immune reactions, promoting healthy wound healing, and curbing excessive fibrosis. The identified proteins adhering to rougher surfaces shed light on potential mediators of pro-inflammatory and pro-fibrotic processes, further emphasizing the need for meticulous consideration of surface design. The composition of the implant capsule and the discovery of intracapsular HSP60 expression highlight the intricate web of stress responses and immune activation that can impact long-term tissue outcomes.

Modeling Paratuberculosis in Laboratory Animals, Cells, or Tissues: A Focus on Their Applications for Pathogenesis, Diagnosis, Vaccines, and Therapy Studies

Paratuberculosis is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. Paratuberculosis that affects a wide variety of domestic and wild animals. It is considered one of the diseases with the highest economic impact on the ruminant industry. Despite many efforts and intensive research, paratuberculosis control still remains controversial, and the existing diagnostic and immunoprophylactic tools have great limitations. Thus, models play a crucial role in understanding the pathogenesis of infection and disease, and in testing novel vaccine candidates. Ruminant animal models can be restricted by several reasons, related to space requirements, the cost of the animals, and the maintenance of the facilities. Therefore, we review the potential and limitations of the different experimental approaches currently used in paratuberculosis research, focusing on laboratory animals and cell-based models. The aim of this review is to offer a vision of the models that have been used, and what has been achieved or discovered with each one, so that the reader can choose the best model to answer their scientific questions and prove their hypotheses. Also, we bring forward new approaches that we consider worth exploring in the near future.

Cell-targeted vaccines: implications for adaptive immunity

Recent advancements in immunology and chemistry have facilitated advancements in targeted vaccine technology. Targeting specific cell types, tissue locations, or receptors can allow for modulation of the adaptive immune response to vaccines. This review provides an overview of cellular targets of vaccines, suggests methods of targeting and downstream effects on immune responses, and summarizes general trends in the literature. Understanding the relationships between vaccine targets and subsequent adaptive immune responses is critical for effective vaccine design. This knowledge could facilitate design of more effective, disease-specialized vaccines.

Bridging the gaps to overcome major hurdles in the development of next-generation tuberculosis vaccines

Although tuberculosis (TB) remains one of the leading causes of death from an infectious disease worldwide, the development of vaccines more effective than bacille Calmette-Guérin (BCG), the only licensed TB vaccine, has progressed slowly even in the context of the tremendous global impact of TB. Most vaccine candidates have been developed to strongly induce interferon-γ (IFN-γ)-producing T-helper type 1 (Th1) cell responses; however, accumulating evidence has suggested that other immune factors are required for optimal protection against Mycobacterium tuberculosis (Mtb) infection. In this review, we briefly describe the five hurdles that must be overcome to develop more effective TB vaccines, including those with various purposes and tested in recent promising clinical trials. In addition, we discuss the current knowledge gaps between preclinical experiments and clinical studies regarding peripheral versus tissue-specific immune responses, different underlying conditions of individuals, and newly emerging immune correlates of protection. Moreover, we propose how recently discovered TB risk or susceptibility factors can be better utilized as novel biomarkers for the evaluation of vaccine-induced protection to suggest more practical ways to develop advanced TB vaccines. Vaccines are the most effective tools for reducing mortality and morbidity from infectious diseases, and more advanced technologies and a greater understanding of host-pathogen interactions will provide feasibility and rationale for novel vaccine design and development.

Protective Effect of BCG and Neutrophil-to-Lymphocyte Ratio on Latent Tuberculosis in End Stage Renal Disease

INTRODUCTION

Bacillus Calmette-Guérin (BCG) vaccination has been reported to be protective against latent tuberculosis infection (LTBI) in the general population. The aim of this study was to investigate the protective effect of BCG vaccination against LTBI in adult patients with end-stage renal disease (ESRD) and renal transplants.

METHODS

Patients aged ≥ 20 years with ESRD who received hemodialysis (HD), peritoneal dialysis (PD) or kidney transplant were enrolled from January 2012 to December 2019 at a medical center and a regional hemodialysis center. Patients with active tuberculosis (TB), previously treated TB, active immunosuppressant therapy or human immunodeficiency virus infection were excluded. LTBI status was determined by QuantiFERON-TB Gold In-tube (QFT-GIT).

RESULTS

After the exclusion of indeterminate results of QFT-GIT, 517 participants were enrolled and 97 (18.8%) were identified as having LTBI. Participants with LTBI were older (55.1 ± 11.4 vs. 48.5 ± 14.6 years, p < 0.001) and had a significantly higher proportion receiving HD than those without LTBI (70.1% vs. 56.7%, p = 0.001). The percentage with BCG scars was higher in the non-LTBI group than in the LTBI group (94.8% vs. 81.4%, p < 0.001), whereas the neutrophil-to-lymphocyte ratio (NLR) (≥ 2.68) was significantly higher in the LTBI group (62.8% vs. 45.5%, p = 0.02). By multivariate logistic regression analysis, presence of BCG scar and high NLR were independent protective factors against LTBI [adjusted OR: 0.19 (0.063-0.58, p = 0.001) and 0.50 (0.28-0.89, p = 0.02)].

CONCLUSION

The prevalence of LTBI was as high as 18.8% in patients with end-stage kidney disease or kidney transplant. BCG vaccination and high NLR might have protective effects against LTBI in patients with renal failure or transplant.

Neutrophils in Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tb) continues to be a leading cause of mortality within developing countries. The BCG vaccine to promote immunity against M. tb is widely used in developing countries and only in specific circumstances within the United States. However, current the literature reports equivocal data on the efficacy of the BCG vaccine. Critical within their role in the innate immune response, neutrophils serve as one of the first responders to infectious pathogens such as M. tb. Neutrophils promote effective clearance of M. tb through processes such as phagocytosis and the secretion of destructive granules. During the adaptative immune response, neutrophils modulate communication with lymphocytes to promote a strong pro-inflammatory response and to mediate the containment M. tb through the production of granulomas. In this review, we aim to highlight and summarize the role of neutrophils during an M. tb infection. Furthermore, the authors emphasize the need for more studies to be conducted on effective vaccination against M. tb.

The roles of neutrophils in non-tuberculous mycobacterial pulmonary disease

Non-tuberculous Mycobacterial Pulmonary Disease (NTM-PD) is an increasingly recognised global health issue. Studies have suggested that neutrophils may play an important role in controlling NTM infection and contribute to protective immune responses within the early phase of infection. However, these cells are also adversely associated with disease progression and exacerbation and can contribute to pathology, for example in the development of bronchiectasis. In this review, we discuss the key findings and latest evidence regarding the diverse functions of neutrophils in NTM infection. First, we focus on studies that implicate neutrophils in the early response to NTM infection and the evidence reporting neutrophils' capability to kill NTM. Next, we present an overview of the positive and negative effects that characterise the bidirectional relationship between neutrophils and adaptive immunity. We consider the pathological role of neutrophils in driving the clinical phenotype of NTM-PD including bronchiectasis. Finally, we highlight the current promising treatments in development targeting neutrophils in airways diseases. Clearly, more insights on the roles of neutrophils in NTM-PD are needed in order to inform both preventative strategies and host-directed therapy for these important infections.

Recombinant BCG expressing the LTAK63 adjuvant improves a short-term chemotherapy schedule in the control of tuberculosis in mice

Tuberculosis (TB) is one of the deadliest infectious diseases around the world. Prevention is based on the prophylactic use of BCG vaccine, effective in infants but as protection wanes with time, adults are less protected. Additionally, chemotherapy requires the use of many antibiotics for several months to be effective. Immunotherapeutic approaches can activate the immune system, intending to assist chemotherapy of TB patients, improving its effectiveness, and reducing treatment time. In this work, the recombinant BCG expressing LTAK63 (rBCG-LTAK63) was evaluated for its immunotherapeutic potential against TB. Bacillary load, immune response, and lung inflammation were evaluated in mice infected with Mycobacterium tuberculosis (Mtb) and treated either with BCG or rBCG-LTAK63 using different routes of administration. Mice infected with Mtb and treated intranasally or intravenously with rBCG-LTAK63 showed a reduced bacillary load and lung inflammatory area when compared to the group treated with BCG. In the spleen, rBCG-LTAK63 administered intravenously induced a higher inflammatory response of CD4+ T cells. On the other hand, in the lungs there was an increased presence of CD4+IL-10+ and regulatory T cells. When combined with a short-term chemotherapy regimen, rBCG-LTAK63 administered subcutaneously or intravenously decreases the Mtb bacillary load, increases the anti-inflammatory response, and reduces tissue inflammation. These findings highlight the potential of rBCG-LTAK63 in assisting chemotherapy against Mtb.

Assessment of Paratuberculosis Vaccination Effect on In Vitro Formation of Neutrophil Extracellular Traps in a Sheep Model

Vaccination of domestic ruminants against paratuberculosis has been related to homologous and heterologous protective effects that have been attributed to the establishment of a trained immune response. Recent evidence suggests that neutrophils could play a role in its development. Therefore, we propose an in vitro model for the study of the effect of paratuberculosis vaccination on the release of neutrophil extracellular traps (NETs) in sheep. Ovine neutrophils were obtained from non-vaccinated (n = 5) and vaccinated sheep (n = 5) at different times post-vaccination and infected in vitro with Mycobacterium avium subsp. paratuberculosis (Map), Staphylococcus aureus (SA), and Escherichia coli (EC). NETs release was quantified by fluorimetry and visualized by immunofluorescence microscopy. Typical NETs components (DNA, neutrophil elastase, and myeloperoxidase) were visualized extracellularly in all infected neutrophils; however, no significant percentage of extracellular DNA was detected in Map-infected neutrophils compared with SA- and EC-infected. In addition, no significant effect was detected in relation to paratuberculosis vaccination. Further assays to study NETs release in ovine neutrophils are needed. Preliminary results suggest no implication of NETs formation in the early immune response after vaccination, although other neutrophil functions should be evaluated.

Neutrophils recruited to immunization sites initiating vaccine-induced antibody responses by locally expressing BAFF

Neutrophils played a key role in the innate immune responses. Less is known about whether and how the neutrophils recruited in the immunization sites affecting the vaccine-induced antibody responses. In the process of evaluating the efficacy of an oil-in-water emulsion-formulated vaccine in mice, we found that neutrophils were rapidly and massively recruited to immunization sites but were barely detected in the draining lymph nodes. Interestingly, B cell-activating factor (BAFF) was abundantly expressed in the recruiting neutrophils at a very early stage. The initial neutrophil-derived BAFF firstly brought about the B cell responses in the local part, then subsequently in lymphoid organs. Activated B cells produced more BAFF through TLR9-IRF5 signaling pathway, thereby amplifying the vaccine-induced antibody responses. Suppressing BAFF in the neutrophils could weaken the B cell activation and reduce the antibody production. The data indicate that vaccines endow neutrophils with the potential to orchestrate antibody responses at immunization sites.

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Neutrophils at immunization sites influencing subsequent immune responses

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Neutrophil-driven BAFF at immunization sites assisting B cell responses to vaccines

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Activated B cells produce more BAFF through TLR9-IRF5 signaling pathway

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BAFF-producing neutrophils orchestrate antibody responses at immunization sites

Mycobacterium bovis PknG R242P Mutation Results in Structural Changes with Enhanced Virulence in the Mouse Model of Infection

Mycobacterium bovis is the causative agent of tuberculosis in domestic and wild animal species and sometimes in humans, presenting variable degrees of pathogenicity. It is known that PknG is involved in the first steps of Mycobacterium tuberculosis macrophage infection and immune evasion. We questioned whether M. bovispknG genes were conserved among mycobacteria and if natural genetic modifications would affect its virulence. We discovered a single mutation at a catalytic domain (R242P) of one M. bovis isolate and established the relation between the presence of R242P mutation and enhanced M. bovis virulence. Here, we demonstrated that R242P mutation alters the PknG protein conformation to a more open ATP binding site cleft. It was observed that M. bovis with PknG mutation resulted in increased growth under stress conditions. In addition, infected macrophages by M. bovis (R242P) presented a higher bacterial load compared with M. bovis without the pknG mutation. Furthermore, using the mouse model of infection, animals infected with M. bovis (R242P) had a massive innate immune response migration to the lung that culminated with pneumonia, necrosis, and higher mortality. The PknG protein single point mutation in its catalytic domain did not reduce the bacterial fitness but rather increased its virulence.

It Takes a Village: The Multifaceted Immune Response to Mycobacterium tuberculosis Infection and Vaccine-Induced Immunity

Despite co-evolving with humans for centuries and being intensely studied for decades, the immune correlates of protection against Mycobacterium tuberculosis (Mtb) have yet to be fully defined. This lapse in understanding is a major lag in the pipeline for evaluating and advancing efficacious vaccine candidates. While CD4+ T helper 1 (TH1) pro-inflammatory responses have a significant role in controlling Mtb infection, the historically narrow focus on this cell population may have eclipsed the characterization of other requisite arms of the immune system. Over the last decade, the tuberculosis (TB) research community has intentionally and intensely increased the breadth of investigation of other immune players. Here, we review mechanistic preclinical studies as well as clinical anecdotes that suggest the degree to which different cell types, such as NK cells, CD8+ T cells, γ δ T cells, and B cells, influence infection or disease prevention. Additionally, we categorically outline the observed role each major cell type plays in vaccine-induced immunity, including Mycobacterium bovis bacillus Calmette-Guérin (BCG). Novel vaccine candidates advancing through either the preclinical or clinical pipeline leverage different platforms (e.g., protein + adjuvant, vector-based, nucleic acid-based) to purposefully elicit complex immune responses, and we review those design rationales and results to date. The better we as a community understand the essential composition, magnitude, timing, and trafficking of immune responses against Mtb, the closer we are to reducing the severe disease burden and toll on human health inflicted by TB globally.

Neutrophil-dendritic cell interaction plays an important role in live attenuated Leishmania vaccine induced immunity

Background

Neutrophils are involved in the initial host responses to pathogens. Neutrophils can activate T cell responses either independently or through indirect involvement of Dendritic cells (DCs). Recently we have demonstrated direct neutrophil-T cell interactions that initiate adaptive immune responses following immunization with live attenuated Leishmania donovani centrin deleted parasite vaccine (LdCen^-/-). However, neutrophil-DC interactions in T cell priming in vaccine immunity in general are not known. In this study we evaluated the interaction between neutrophils and DCs during LdCen^-/- infection and compared with wild type parasite (LdWT) both in vitro and in vivo.

Methodology/findings

LdCen^-/- parasite induced increased expression of CCL3 in neutrophils caused higher recruitment of DCs capable of inducing a strong proinflammatory response and elevated co-stimulatory molecule expression compared to LdWT infection. To further illustrate neutrophil-DCs interactions in vivo, we infected LYS-eGFP mice with red fluorescent LdWT/LdCen^-/- parasites and sort selected DCs that engulfed the neutrophil containing parasites or DCs that acquired the parasites directly in the ear draining lymph nodes (dLN) 5d post infection. The DCs predominantly acquired the parasites by phagocytosing infected neutrophils. Specifically, DCs containing LdCen^-/- parasitized neutrophils exhibited a proinflammatory phenotype, increased expression of costimulatory molecules and initiated higher CD4⁺T cell priming ex-vivo. Notably, potent DC activation occurred when LdCen^-/- parasites were acquired indirectly via engulfment of parasitized neutrophils compared to direct engulfment of LdCen^-/- parasites by DCs. Neutrophil depletion in LdCen^-/- infected mice significantly abrogated expression of CCL3 resulting in decreased DC recruitment in ear dLN. This event led to poor CD4⁺Th1 cell priming ex vivo that correlated with attenuated Tbet expression in ear dLN derived CD4⁺ T cells in vivo.

Conclusions

Collectively, LdCen^-/- containing neutrophils phagocytized by DC markedly influence the phenotype and antigen presenting capacity of DCs early on and thus play an immune-regulatory role in shaping vaccine induced host protective response.

Visceral Leishmaniasis (VL), caused by the protozoan parasites of the genus Leishmania is a neglected tropical disease. Leishmania donovani is the principal causative agent of VL in East Africa and the Indian subcontinent whereas in Europe, North Africa, and Latin America VL is mainly caused by Leishmania infantum. No licensed vaccine exists against VL. We have reported previously that live attenuated centrin gene-deleted L. donovani (LdCen^-/-) parasite vaccine induced strong innate immunity which leads to a protective Th1 response in animal models. We recently demonstrated that neutrophils play an indispensable role following immunization with LdCen^-/- parasites in inducing protective Th1 immune response. However, neutrophils also secrete chemokines that attract other innate cells such as dendritic cells and regulate their activities. In the current study we analyzed the interplay between neutrophils and DCs, and its effects on T cell activation during LdCen^-/- infection and compared with wild type parasite (LdWT) infection. We observed that higher recruitment of DCs occurred in LdCen^-/- infected mice ear draining lymph nodes compared to LdWT. This recruitment is facilitated by increased secretion of the chemokine CCL3 by neutrophils. A markedly decreased DC recruitment was observed in LdCen^-/- infected mice following CCL3 neutralization indicating the key role of neutrophils in DC recruitment. Further, we demonstrated that DCs that ingest LdCen^-/- infected neutrophils are better activated than those that acquire the parasites independent of neutrophils. Notably neutrophil depletion in LdCen^-/- infected mice also attenuated activation of DCs in the ear dLN that resulted in poor CD4⁺T cell priming. Our results reveal that interaction between neutrophils and DCs play an important role in shaping proinflammatory immune response induced by a live attenuated Leishmania vaccine.

Immunological Assessment of Chitosan or Trimethyl Chitosan-Coated PLGA Nanospheres Containing Fusion Antigen as the Novel Vaccine Candidates Against Tuberculosis

The crucial challenge in tuberculosis (TB) as a chronic infectious disease is to present a novel vaccine candidate that improves current vaccination and provides efficient protection in individuals. The present study aimed to evaluate the immune efficacy of multi-subunit vaccines containing chitosan (CHT)- or trimethyl chitosan (TMC)-coated PLGA nanospheres to stimulate cell-mediated and mucosal responses against Mycobacterium Tuberculosis (Mtb) in an animal model. The surface-modified PLGA nanoparticles (NPs) containing tri-fusion protein from three Mtb antigens were produced by the double emulsion technique. The subcutaneously or nasally administered PLGA vaccines in the absence or presence of BCG were assessed to compare the levels of mucosal IgA, IgG1, and IgG2a production as well as secretion of IFN-γ, IL-17, IL-4, and TGF-β cytokines. According to the release profile, the tri-fusion encapsulated in modified PLGA NPs demonstrated a biphasic release profile including initial burst release on the first day and sustained release within 18 days. All designed PLGA vaccines induced a shift of Th1/Th2 balance toward Th1-dominant response. Although immunized mice through subcutaneous injection elicited higher cell-mediated responses relative to the nasal vaccination, the intranasally administered groups stimulated robust mucosal IgA immunity. The modified PLGA NPs using TMC cationic polymer were more efficient to elevate Th1 and mucosal responses in comparison with the CHT-coated PLGA nanospheres. Our findings highlighted that the tri-fusion loaded in TMC-PLGA NPs may represent an efficient prophylactic vaccine and can be considered as a novel candidate against TB.

Our evolving view of neutrophils in defining the pathology of chronic lung disease

Neutrophils are critical components of the body's immune response to infection, being loaded with a potent arsenal of toxic mediators and displaying immense destructive capacity. Given the potential of neutrophils to impart extensive tissue damage, it is perhaps not surprising that when augmented these cells are also implicated in the pathology of inflammatory diseases. Prominent neutrophilic inflammation is a hallmark feature of patients with chronic lung diseases such as chronic obstructive pulmonary disease, severe asthma, bronchiectasis and cystic fibrosis, with their numbers frequently associating with worse prognosis. Accordingly, it is anticipated that neutrophils are central to the pathology of these diseases and represent an attractive therapeutic target. However, in many instances, evidence directly linking neutrophils to the pathology of disease has remained somewhat circumstantial and strategies that have looked to reduce neutrophilic inflammation in the clinic have proved largely disappointing. We have classically viewed neutrophils as somewhat crude, terminally differentiated, insular and homogeneous protagonists of pathology. However, it is now clear that this does not do the neutrophil justice, and we now recognize that these cells exhibit heterogeneity, a pronounced awareness of the localized environment and a remarkable capacity to interact with and modulate the behaviour of a multitude of cells, even exhibiting anti-inflammatory, pro-resolving and pro-repair functions. In this review, we discuss evidence for the role of neutrophils in chronic lung disease and how our evolving view of these cells may impact upon our perceived assessment of their contribution to disease pathology and efforts to target them therapeutically.

Determinants of Innate Immunity in Visceral Leishmaniasis and Their Implication in Vaccine Development

Leishmaniasis is endemic to the tropical and subtropical regions of the world and is transmitted by the bite of an infected sand fly. The multifaceted interactions between Leishmania, the host innate immune cells, and the adaptive immunity determine the severity of pathogenesis and disease development. Leishmania parasites establish a chronic infection by subversion and attenuation of the microbicidal functions of phagocytic innate immune cells such as neutrophils, macrophages and dendritic cells (DCs). Other innate cells such as inflammatory monocytes, mast cells and NK cells, also contribute to resistance and/or susceptibility to Leishmania infection. In addition to the cytokine/chemokine signals from the innate immune cells, recent studies identified the subtle shifts in the metabolic pathways of the innate cells that activate distinct immune signal cascades. The nexus between metabolic pathways, epigenetic reprogramming and the immune signaling cascades that drive the divergent innate immune responses, remains to be fully understood in Leishmania pathogenesis. Further, development of safe and efficacious vaccines against Leishmaniasis requires a broader understanding of the early interactions between the parasites and innate immune cells. In this review we focus on the current understanding of the specific role of innate immune cells, the metabolomic and epigenetic reprogramming and immune regulation that occurs during visceral leishmaniasis, and the strategies used by the parasite to evade and modulate host immunity. We highlight how such pathways could be exploited in the development of safe and efficacious Leishmania vaccines.

Oral vaccination stimulates neutrophil functionality and exerts protection in a Mycobacterium avium subsp. paratuberculosis infection model

Mycobacterium avium subsp. paratuberculosis (Map) causes paratuberculosis (PTB), a granulomatous enteritis in ruminants that exerts high economic impact on the dairy industry worldwide. Current vaccines have shown to be cost-effective against Map and in some cases confer beneficial non-specific effects against other pathogens suggesting the existence of trained immunity. Although Map infection is mainly transmitted by the fecal-oral route, oral vaccination has not been deeply studied. Therefore, the aim of this study was to compare the oral route with a set of mycobacterial and non-mycobacterial vaccines with a subcutaneously administered commercially available vaccine. Training effects on polymorphonuclear neutrophils (PMNs) and homologous and heterologous in vivo protection against Map were investigated in the rabbit infection model. Oral vaccination with inactivated or live vaccines was able to activate mucosal immunity as seen by elevation of serum IgA and the expression of IL4 in peripheral blood mononuclear cells (PBMCs). In addition, peripheral PMN phagocytosis against Map was enhanced by vaccination and extracellular trap release against Map and non-related pathogens was modified by both, vaccination and Map-challenge, indicating trained immunity. Finally, PBMCs from vaccinated animals stimulated in vitro with Map antigens showed a rapid innate activation cytokine profile. In conclusion, our data show that oral vaccination against PTB can stimulate neutrophil activity and both innate and adaptive immune responses that correlate with protection.

Neutrophil Cells Are Essential for The Efficacy of a Therapeutic Vaccine against Paracoccidioidomycosis

Paracoccidioidomycosis (PCM), caused by the Paracoccidioides species, is a systemic disease endemic in several Latin American countries, mainly in Brazil, Colombia, Argentina, and Venezuela. Current treatment approaches are challenging as they require prolonged durations of antifungal drugs that have potential toxicities, and despite antifungals, relapses are common. Hence, new therapeutic approaches, such as vaccines, are being investigated. The therapeutic vaccine consisting of peptide P10 associated with lipid cationic DODAB (P10+DODAB) is effective in murine models of PCM. However, the specific immune mechanisms required for the protective response has not been fully elucidated. The present work aims at evaluating the participation of neutrophils in the immune response induced by P10+DODAB. We found that the vaccine reduced both the influx of pulmonary neutrophils and the fungal load in comparison to infected animals that did not receive this treatment. The parenchymal architecture of the lungs of P10+DODAB-treated animals was largely preserved with only a few granulomas present, and tissue cytokine analysis showed a Th1 cytokine profile with augmented levels of IL-12, IFN-γ and TNF-α, and low levels of IL-4. When neutrophils were depleted 24 h prior to each treatment, the effectiveness of the P10+DODAB vaccine was completely lost as the fungal burdens remained high and histological examination showed a marked inflammation and fungal dissemination with a dysregulated cytokine response. In conclusion, these findings indicate that neutrophils are vital to ensure the triggering of an effective immune response to P10+DODAB.

Older but Not Wiser: the Age-Driven Changes in Neutrophil Responses during Pulmonary Infections

Elderly individuals are at increased risk of life-threatening pulmonary infections. Neutrophils are a key determinant of the disease course of pathogen-induced pneumonia. Optimal host defense balances initial robust pulmonary neutrophil responses to control pathogen numbers, ultimately followed by the resolution of inflammation to prevent pulmonary damage. Recent evidence suggests that phenotypic and functional heterogeneity in neutrophils impacts host resistance to pulmonary pathogens. Apart from their apparent role in innate immunity, neutrophils also orchestrate subsequent adaptive immune responses during infection. Thus, the outcome of pulmonary infections can be shaped by neutrophils. This review summarizes the age-driven impairment of neutrophil responses and the contribution of these cells to the susceptibility of the elderly to pneumonia. We describe how aging is accompanied by changes in neutrophil recruitment, resolution, and function. We discuss how systemic and local changes alter the neutrophil phenotype in aged hosts. We highlight the gap in knowledge of whether these changes in neutrophils also contribute to the decline in adaptive immunity seen with age. We further detail the factors that drive dysregulated neutrophil responses in the elderly and the pathways that may be targeted to rebalance neutrophil activity and boost host resistance to pulmonary infections.

Metabolic Regulation of Immune Responses to Mycobacterium tuberculosis: A Spotlight on L-Arginine and L-Tryptophan Metabolism

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a leading cause of death worldwide. Despite decades of research, there is still much to be uncovered regarding the immune response to Mtb infection. Here, we summarize the current knowledge on anti-Mtb immunity, with a spotlight on immune cell amino acid metabolism. Specifically, we discuss L-arginine and L-tryptophan, focusing on their requirements, regulatory roles, and potential use as adjunctive therapy in TB patients. By continuing to uncover the immune cell contribution during Mtb infection and how amino acid utilization regulates their functions, it is anticipated that novel host-directed therapies may be developed and/or refined, helping to eradicate TB.

Essential Role of Neutrophils in the Protective Immune Response Induced by a Live Attenuated Leishmania Vaccine

No licensed vaccine exists against visceral leishmaniasis (VL), a disease caused by the Leishmania donovani parasite. We have previously reported both macrophages and dendritic cells play important role in the protection induced by a live attenuated centrin gene-deleted L. donovani (LdCen^-/- ) parasite vaccine. The role of neutrophils in orchestrating the initial innate response to pathogens is widely recognized. To investigate the early interaction of LdCen^-/- with neutrophils, we immunized mice intradermally in the ear pinna with LdCen^-/- Compared with LdWT infection, LdCen^-/- parasites induced higher recruitment of neutrophils to the ear dermis and ear draining lymph nodes (dLN) as early as 6-18 h after immunization, which were predominantly proinflammatory in nature. Neutrophils from ear dLN of LdCen^-/- -immunized mice exhibited heightened expression of costimulatory molecules and attenuated expression of coinhibitory molecules necessary for higher T cell activation. Further phenotypic characterization revealed heterogeneous neutrophil populations containing Nα and Nβ subtypes in the ear dLN. Of the two, the parasitized Nα subset from LdCen^-/- -immunized mice exhibited much stronger Ag-specific CD4⁺ T cell proliferation ex vivo. Adoptive transfer of neutrophils bearing LdCen^-/- parasites induced an increased Th1 response in naive mice. Importantly, neutrophil depletion significantly abrogated Ag-specific CD4⁺ T cell proliferation in LdCen^-/- -immunized mice and impaired protection against virulent challenge. Conversely, replenishing of neutrophils significantly restored the LdCen^-/- -induced host-protective response. These results suggest that neutrophils are indispensable for protective immunity induced by LdCen^-/- parasite vaccine.

Immunodominant Mycobacterium tuberculosis Protein Rv1507A Elicits Th1 Response and Modulates Host Macrophage Effector Functions

Mycobacterium tuberculosis (M. tb) persists as latent infection in nearly a quarter of the global population and remains the leading cause of death among infectious diseases. While BCG is the only vaccine for TB, its inability to provide complete protection makes it imperative to engineer BCG such that it expresses immunodominant antigens that can enhance its protective potential. In-silico comparative genomic analysis of Mycobacterium species identified M. tb Rv1507A as a “signature protein” found exclusively in M. tb. In-vitro (cell lines) and in-vivo experiments carried out in mice, using purified recombinant Rv1507A revealed it to be a pro-inflammatory molecule, eliciting significantly high levels of IL-6, TNF-α, and IL-12. There was increased expression of activation markers CD69, CD80, CD86, antigen presentation molecules (MHC I/MHCII), and associated Th1 type of immune response. Rv1507A knocked-in M. smegmatis also induced significantly higher pro-inflammatory Th1 response and higher survivability under stress conditions, both in-vitro (macrophage RAW264.7 cells) and in-vivo (mice). Sera derived from human TB patients showed significantly enhanced B-cell response against M. tb Rv1507A. The ability of M. tb Rv1507A to induce immuno-modulatory effect, B cell response, and significant memory response, renders it a putative vaccine candidate that demands further exploration.

Characterizing the BCG Induced Macrophage and Neutrophil Mechanisms for Defense Against Mycobacterium tuberculosis

The live attenuated Mycobacterium bovis strain, Bacille Calmette Guérin (BCG) is a potent innate immune stimulator. In the C57BL/6 mouse model of tuberculosis, BCG vaccination leads to a significant reduction of Mycobacterium tuberculosis burden after aerogenic infection. Our studies indicated that BCG induced protection against pulmonary tuberculosis was independent of T cells and present as early as 7 days after vaccination. This protection showed longevity, as it did not wane when conventional T cell and TNF-α deficient mice were infected 30 days post-vaccination. As BCG induced mycobacterial killing after 7 days, this study investigated the contributions of the innate immune system after BCG vaccination to better understand mechanisms required for mycobacterial killing. Subcutaneous BCG inoculation resulted in significant CD11b⁺F4/80⁺ monocyte subset recruitment into the lungs within 7 days. Further studies revealed that killing of mycobacteria was dependent on the viability of BCG, because irradiated BCG did not have the same effect. Although others have identified BCG as a facilitator of trained innate immunity, we found that BCG reduced the mycobacterial burden in the absence of mechanisms required for trained innate immunity, highlighting a role for macrophages and neutrophils for vaccine induced killing of M. tuberculosis.

Role of neutrophils in tuberculosis: A bird's eye view

Neutrophils are innate immune cells implicated in the process of killing Mycobacterium tuberculosis early during infection. Once the mycobacteria enter the human system, neutrophils sense and engulf them. By secreting bactericidal enzymes and α-defensins like human neutrophil peptides loaded in their granule armory, neutrophils kill the pathogen. Peripheral blood neutrophils secrete a wide range of cytokines like IL-8, IL-1-β and IFN-γ in response to mycobacterial infection. Thus they signal and activate distant immune cells thereby informing them of prevailing infection. The activated monocytes, dendritic cells and T cells further continue the immune response. As a final call, neutrophils release neutrophil extracellular traps in circulation which can trap mycobacteria in patients with active pulmonary tuberculosis. Extensive neutrophilic response is associated with inflammation, pulmonary destruction, and pathology. For example, inappropriate phagocytosis of mycobacteria-infected neutrophils can damage host cells due to necrosis of neutrophils, leading to chronic inflammation and tissue damage. This dual nature of neutrophils makes them double-edged swords during tuberculosis, and hence data available on neutrophil functions against mycobacterium are controversial and non-uniform. This article reviews the role of neutrophils in tuberculosis infection and highlights research gaps that need to be addressed. We focus on our understanding of new research ideologies targeting neutrophils (a) in the early stages of infection for boosting specific immune functions or (b) in the later stages of infection to prevent inflammatory conditions mediated by activated neutrophils. This would plausibly lead to the development of better tuberculosis vaccines and therapeutics in the future.

Live Vaccines Have Different NK Cells and Neutrophils Requirements for the Development of a Protective Immune Response Against Tuberculosis

It has been shown that neutrophils drive NK cells to activate DCs while NK cells regulate neutrophils survival. In response to mycobacteria, NK cells proliferate and produces IFN-γ, that appears to regulate the neutrophilic inflammatory responses to both M. tuberculosis infection and BCG vaccination. Although the role of neutrophils in the immune response to tuberculosis is a matter of debate, neutrophils were shown to be crucial to induce specific response against mc²-CMX vaccine. The objective of this study was to investigate the interplay between NK cells and neutrophils in regard to the development of a protective immune response against M. tuberculosis. Depletion of NK cells during vaccination did not alter the total number of neutrophils or DCs, but reduced the number of activated DCs, thus reducing the generation of Th1 specific immune responses and the protection conferred by mc²-CMX and BCG vaccines. However, only in mc²-CMX vaccination that neutrophil depletion interfered with the NK cell numbers and protection. In conclusion, it was shown that only when both NK and neutrophils were present, specific Th1 response and protection was achieved by mc²-CMX vaccine, while neutrophils although activated upon BCG vaccination were not necessary for the induced protection.

Advanced Glycated End Products Alter Neutrophil Effect on Regulation of CD4+ T Cell Differentiation Through Induction of Myeloperoxidase and Neutrophil Elastase Activities

CD₄⁺ T cell subset imbalance plays an important role in the development of diabetic complications. Neutrophils have recently been known as the regulator of CD₄⁺ T cell differentiation. However, whether neutrophils affect CD₄⁺ T cell population in diabetes is still elusive. In this study, we investigated the effect of neutrophils stimulated with advanced glycated end products (AGEs), the marker of diabetes, on CD₄⁺ T cell differentiation and its underlying mechanism. Our data showed that the cultural medium of healthy adult neutrophils treated with AGEs increased expressions of both Th₁ (IFN-γ) and Th₁₇ (IL-17) phenotypes and the transcription factors of Th₁ (Tbet) and Th₁₇ (RORγt) in naive CD₄⁺T cells and CD₄⁺CD₂₅⁺FoxP₃⁺ (Treg) T cells in vitro. Next, we found that AGEs induced the generations of myeloperoxidase (MPO) and neutrophil elastase (NE) in neutrophils; inhibition of MPO or NE attenuated the effect of AGE-stimulated neutrophils on CD₄⁺ T cell bias. Furthermore, receptor for AGEs (RAGE) inhibitor interrupted AGE-induced MPO and NE expressions, but MPO and NE inhibitions did not change AGE-increased RAGE gene expression. These results suggested that AGEs drive the effect of neutrophils on CD₄⁺ T cell differentiation into pro-inflammatory program through inducing MPO and NE productions in neutrophils, which is mediated by AGE-RAGE interaction.

Cell Differentiation Degree as a Factor Determining the Role for Different T-Helper Populations in Tuberculosis Protection

Efficient tuberculosis (TB) control depends on early TB prediction and prevention. Solution to these tasks requires knowledge of TB protection correlates (TB CoPs), i.e., laboratory markers that are mechanistically involved in the protection and which allow to determine how well an individual is protected against TB or how efficient the candidate TB vaccine is. The search for TB CoPs has been largely focused on different T-helper populations, however, the data are controversial, and no reliable CoPs are still known. Here we discuss the role of different T-helper populations in TB protection focusing predominantly on Th17, “non-classical” Th1 (Th1^*) and “classical” Th1 (cTh1) populations. We analyze how these populations differ besides their effector activity and suggest the hypothesis that: (i) links the protective potential of Th17, Th1^*, and cTh1 to their differentiation degree and plasticity; (ii) implies different roles of these populations in response to vaccination, latent TB infection (LTBI), and active TB. One of the clinically relevant outcomes of this hypothesis is that over-stimulating T cells during vaccination and biasing T cell response toward the preferential generation of Th1 are not beneficial. The review sheds new light on the problem of TB CoPs and will help develop better strategies for TB control.

Immunity to the Dual Threat of Silica Exposure and Mycobacterium tuberculosis

Exposure to silica and the consequent development of silicosis are well-known health problems in countries with mining and other dust producing industries. Apart from its direct fibrotic effect on lung tissue, chronic and immunomodulatory character of silica causes susceptibility to tuberculosis (TB) leading to a significantly higher TB incidence in silica-exposed populations. The presence of silica particles in the lung and silicosis may facilitate initiation of tuberculous infection and progression to active TB, and exacerbate the course and outcome of TB, including prognosis and survival. However, the exact mechanisms of the involvement of silica in the pathological processes during mycobacterial infection are not yet fully understood. In this review, we focus on the host's immunological response to both silica and Mycobacterium tuberculosis, on agents of innate and adaptive immunity, and particularly on silica-induced immunological modifications in co-exposure that influence disease pathogenesis. We review what is known about the impact of silica and Mycobacterium tuberculosis or their co-exposure on the host's immune system, especially an impact that goes beyond an exclusive focus on macrophages as the first line of the defense. In both silicosis and TB, acquired immunity plays a major role in the restriction and/or elimination of pathogenic agents. Further research is needed to determine the effects of silica in adaptive immunity and in the pathogenesis of TB.

Recent advances on the crosstalk between neutrophils and B or T lymphocytes

An increasing body of literature supports a role for neutrophils as players in the orchestration of adaptive immunity. During acute and chronic inflammatory conditions, neutrophils rapidly migrate not only to sites of inflammation, but also to draining lymph nodes and spleen, where they engage bidirectional interactions with B- and T-lymphocyte subsets. Accordingly, a relevant role of neutrophils in modulating B-cell responses under homeostatic conditions has recently emerged. Moreover, specialized immunoregulatory properties towards B or T cells acquired by distinct neutrophil populations, originating under pathological conditions, have been consistently described. In this article, we summarize the most recent data from human studies and murine models on the ability of neutrophils to modulate adaptive immune responses under physiological and pathological conditions and the mechanisms behind these processes.

Improvement of the resistance against early Mycobacterium tuberculosis-infection in the absence of PI3Kγ enzyme is associated with increase of CD4+IL-17+ cells and neutrophils

Given the impossibility to study the lung immune response during Mycobacterium tuberculosis-latent infection, and consequently, the mechanisms that control the bacterial load, it is reasonable to determine the activation of local immunity in the early phase of the infection. The phosphatidylinositol-3-kinase gamma enzyme (PI3Kγ) is involved in the leukocyte recruitment, phagocytosis and cellular differentiation, and therefore, it is considered a promising target for the development of immunotherapies for chronic inflammatory diseases. Mice genetically deficient in PI3Kγ (PI3Kγ^-/-) or WT (Wild Type) were evaluated 15 days post-infection. The enzyme deficiency improved the resistance against infection, increased the frequency of CD4⁺IL-17⁺ cells, the production of IL-17 as well as the gene and protein expression of molecules associated with Th17 cell differentiation and neutrophil recruitment. Our findings show, for the first time, the participation of the PI3Kγ in vivo in the M. tuberculosis-infection, and suggest an association of Th17 cells with protection in the early phase of tuberculosis.

Specific T cell induction using iron oxide based nanoparticles as subunit vaccine adjuvant

Metal-based nanoparticles (NPs) stimulate innate immunity; however, they have never been demonstrated to be capable of aiding the generation of specific cellular immune responses. Therefore, our objective was to evaluate whether iron oxide-based NPs have adjuvant properties in generating cellular Th1, Th17 and TCD8 (Tc1) immune responses. For this purpose, a fusion protein (CMX) composed of Mycobacterium tuberculosis antigens was used as a subunit vaccine. Citrate-coated MnFe₂O₄ NPs were synthesized by co-precipitation and evaluated by transmission electron microscopy. The vaccine was formulated by homogenizing NPs with the recombinant protein, and protein corona formation was determined by dynamic light scattering and field-emission scanning electron microscopy. The vaccine was evaluated for the best immunization route and strategy using subcutaneous and intranasal routes with 21-day intervals between immunizations. When administered subcutaneously, the vaccine generated specific CD4⁺IFN-γ⁺ (Th1) and CD8⁺IFN-γ⁺ responses. Intranasal vaccination induced specific Th1, Th17 (CD4⁺IL-17⁺) and Tc1 responses, mainly in the lungs. Finally, a mixed vaccination strategy (2 subcutaneous injections followed by one intranasal vaccination) induced a Th1 (in the spleen and lungs) and splenic Tc1 response but was not capable of inducing a Th17 response in the lungs. This study shows for the first time a subunit vaccine with iron oxide based NPs as an adjuvant that generated cellular immune responses (Th1, Th17 and TCD8), thereby exhibiting good adjuvant qualities. Additionally, the immune response generated by the subcutaneous administration of the vaccine diminished the bacterial load of Mtb challenged animals, showing the potential for further improvement as a vaccine against tuberculosis.

Advax4 delta inulin combination adjuvant together with ECMX, a fusion construct of four protective mTB antigens, induces a potent Th1 immune response and protects mice against Mycobacterium tuberculosis infection

Tuberculosis (TB) remains a main public health concern and 10.4 million new cases occurred in 2015 around the world. BCG is the only approved vaccine against TB, but has variable efficacy and new vaccines are needed. We developed two new mTB vaccine candidates based on the recombinant fusion proteins, rCMX and rECMX formulated with Advax4, a new combination adjuvant combining delta inulin, CpG oligonucleotide and murabutide. BALB/c mice were immunized three times intramuscularly with these vaccine formulations. Injection of Advax4 alone increased the percentage of lymphatic endothelial cells and activated macrophages (F480/CD11b⁺) in the draining lymph nodes consistent with a chemotactic adjuvant effect. Advax4+CMX and Advax4+ECMX induced the highest levels of IgG1 and IgG2a antibodies against rCMX and rECMX, respectively. Immunized mice challenged with Mycobacterium tuberculosis (Mtb) had increased vaccine-specific Th1 responses in the lungs together with reduced Mtb - associated alveolar damage, although only the Advax4+ECMX vaccine demonstrated significant reduction of lung bacterial load. This study confirmed Advax4+ECMX as a potential TB vaccine candidate, with potential for further optimization and clinical development.

The Immunoregulation of Th17 in Host against Intracellular Bacterial Infection

T helper 17 cells (Th17) constitute a distinct subset of helper T cells with a unique transcriptional profile (STAT3, RORγ, and RORα), cytokine production pattern (IL17 family), and requirement of specific cytokines for their differentiation (TGF-β, IL6, IL21, and IL23). Recent studies involving experimental animals and humans have shown that Th17/IL17 plays a crucial role in host defense against a variety of pathogens, including bacteria and viruses. The underlying mechanisms by which Th17 performs include dendritic cell (DC) regulation, neutrophil recruitment, Th1 modulation, and T regulatory cell (Treg) balance. In recent years, researchers have generated an accumulating wealth of evidence on the role of Th17/IL17 in protective immunity to intracellular bacterial pathogens, such as Mycobacterium tuberculosis and Chlamydia trachomatis, which are one of the most important pathogens that inflict significant socioeconomic burden across the globe. In this article, we reviewed the current literature on the functions and mechanisms by which Th17/IL17 responds to intracellular bacterial infections. A better understanding of Th17/IL17 immunity to pathogens would be crucial for developing effective prophylactics and therapeutics.

Strategies to Improve Vaccine Efficacy against Tuberculosis by Targeting Innate Immunity

The global tuberculosis epidemic is the most common cause of death after infectious disease worldwide. Increasing numbers of infections with multi- and extensively drug-resistant variants of the Mycobacterium tuberculosis complex, resistant even to newly discovered and last resort antibiotics, highlight the urgent need for an efficient vaccine. The protective efficacy to pulmonary tuberculosis in adults of the only currently available vaccine, M. bovis BCG, is unsatisfactory and geographically diverse. More importantly, recent clinical studies on new vaccine candidates did not prove to be better than BCG, yet. Here, we propose and discuss novel strategies to improve efficacy of existing anti-tuberculosis vaccines. Modulation of innate immune responses upon vaccination already provided promising results in animal models of tuberculosis. For instance, neutrophils have been shown to influence vaccine efficacy, both, positively and negatively, and stimulate specific antibody secretion. Modulating immune regulatory properties after vaccination such as induction of different types of innate immune cell death, myeloid-derived suppressor or regulatory T cells, production of anti-inflammatory cytokines such as IL-10 may have beneficial effects on protection efficacy. Incorporation of lipid antigens presented via CD1 molecules to T cells have been discussed as a way to enhance vaccine efficacy. Finally, concepts of dendritic cell-based immunotherapies or training the innate immune memory may be exploitable for future vaccination strategies against tuberculosis. In this review, we put a spotlight on host immune networks as potential targets to boost protection by old and new tuberculosis vaccines.

Neutrophils in Tuberculosis: Heterogeneity Shapes the Way?

Infection with M. tuberculosis remains one of the most common infections in the world. The outcome of the infection depends on host ability to mount effective protection and balance inflammatory responses. Neutrophils are innate immune cells implicated in both processes. Accordingly, during M. tuberculosis infection, they play a dual role. Particularly, they contribute to the generation of effector T cells, participate in the formation of granuloma, and are directly involved in tissue necrosis, destruction, and infection dissemination. Neutrophils have a high bactericidal potential. However, data on their ability to eliminate M. tuberculosis are controversial, and the results of neutrophil depletion experiments are not uniform. Thus, the overall roles of neutrophils during M. tuberculosis infection and factors that determine these roles are not fully understood. This review analyzes data on neutrophil defensive and pathological functions during tuberculosis and considers hypotheses explaining the dualism of neutrophils during M. tuberculosis infection and tuberculosis disease.

Interactions between Type 1 Interferons and the Th17 Response in Tuberculosis: Lessons Learned from Autoimmune Diseases

The classical paradigm of tuberculosis (TB) immunity, with a central protective role for Th1 responses and IFN-γ-stimulated cellular responses, has been challenged by unsatisfactory results of vaccine strategies aimed at enhancing Th1 immunity. Moreover, preclinical TB models have shown that increasing IFN-γ responses in the lungs is more damaging to the host than to the pathogen. Type 1 interferon signaling and altered Th17 responses have also been associated with active TB, but their functional roles in TB pathogenesis remain to be established. These two host responses have been studied in more detail in autoimmune diseases (AID) and show functional interactions that are of potential interest in TB immunity. In this review, we first identify the role of type 1 interferons and Th17 immunity in TB, followed by an overview of interactions between these responses observed in systemic AID. We discuss (i) the effects of GM-CSF-secreting Th17.1 cells and type 1 interferons on CCR2⁺ monocytes; (ii) convergence of IL-17 and type 1 interferon signaling on stimulating B-cell activating factor production and the central role of neutrophils in this process; and (iii) synergy between IL-17 and type 1 interferons in the generation and function of tertiary lymphoid structures and the associated follicular helper T-cell responses. Evaluation of these autoimmune-related pathways in TB pathogenesis provides a new perspective on recent developments in TB research.

Effector Mechanisms of Neutrophils within the Innate Immune System in Response to Mycobacterium tuberculosis Infection

Neutrophils have a significant yet controversial role in the innate immune response to Mycobacterium tuberculosis (M. tb) infection, which is not yet fully understood. In addition to neutrophils’ well-known effector mechanisms, they may also help control infection of M. tb through the formation of neutrophil extracellular traps (NETs), which are thought to further promote the killing of M. tb by resident alveolar macrophages. Cytokines such as IFN-γ have now been shown to serve an immunomodulatory role in neutrophil functioning in conjunction to its pro-inflammatory function. Additionally, the unique transcriptional changes of neutrophils may be used to differentiate between infection with M. tb and other bacterial and chronic rheumatological diseases such as Systemic Lupus Erythematosus. Adversely, during the innate immune response to M. tb, inappropriate phagocytosis of spent neutrophils can result in nonspecific damage to host cells due to necrotic lysis. Furthermore, some individuals have been shown to be more genetically susceptible to tuberculosis (TB) due to a “Trojan Horse” phenomenon whereby neutrophils block the ability of resident macrophages to kill M. tb. Despite these aforementioned negative consequences, through the scope of this review we will provide evidence to support the idea that neutrophils, while sometimes damaging, can also be an important component in warding off M. tb infection. This is exemplified in immunocompromised individuals, such as those with human immunodeficiency virus (HIV) infection or Type 2 diabetes mellitus. These individuals are at an increased risk of developing tuberculosis (TB) due to a diminished innate immune response associated with decreased levels of glutathione. Consequently, there has been a worldwide effort to limit and contain M. tb infection through the use of antibiotics and vaccinations. However, due to several significant limitations, the current bacille Calmette-Guerin vaccine (BCG, vaccine against TB) does not meet the criteria for universal utilization for all ages and populations across the globe. New research involving neutrophils has yielded a new vaccine called M. smegmatis-Ag85C-MPT51-HspX (mc²-CMX) that has been shown to elicit a humoral and cellular response against M. tb in mice that is superior to the BCG vaccine.

Neutrophil plasticity enables the development of pathological microenvironments: implications for cystic fibrosis airway disease

INTRODUCTION

The pathological course of several chronic inflammatory diseases, including cystic fibrosis, chronic obstructive pulmonary disease, and rheumatoid arthritis, features an aberrant innate immune response dominated by neutrophils. In cystic fibrosis, neutrophil burden and activity of neutrophil elastase in the extracellular fluid have been identified as strong predictors of lung disease severity.

REVIEW

Although neutrophils are generally considered to be rigid, pre-programmed effector leukocytes, recent studies suggest extensive plasticity in how neutrophil functions unfold upon recruitment to peripheral tissues, and how they choose their ultimate fate. Indeed, upon migration to cystic fibrosis airways, neutrophils display dysregulated lifespan, metabolic activation, and altered effector and regulatory functions, consistent with profound adaptation and phenotypic reprogramming. Licensed by signals present in cystic fibrosis airway microenvironment to survive and develop these novel functions, neutrophils orchestrate, in partnership with the epithelium and with the resident microbiota, the evolution of a pathological microenvironment. This microenvironment is defined by altered proteolytic, redox, and metabolic balance and the presence of stable luminal structures in which neutrophils and microbes coexist.

CONCLUSIONS

The elucidation of molecular mechanisms driving neutrophil plasticity in vivo will open new treatment opportunities designed to modulate, rather than block, the crucial adaptive functions fulfilled by neutrophils. This review aims to outline emerging mechanisms of neutrophil plasticity and their participation in the building of pathological microenvironments in the context of cystic fibrosis and other diseases with similar features.