In a murine tuberculosis model, the absence of homeostatic chemokines delays granuloma formation and protective immunity

Integrative and comparative genomic analyses of mammalian macrophage responses to intracellular mycobacterial pathogens

Mycobacterium tuberculosis, the causative agent of human tuberculosis (hTB), is a close evolutionary relative of Mycobacterium bovis, which causes bovine tuberculosis (bTB), one of the most damaging infectious diseases to livestock agriculture. Previous studies have shown that the pathogenesis of bTB disease is comparable to hTB disease, and that the bovine and human alveolar macrophage (bAM and hAM, respectively) transcriptomes are extensively reprogrammed in response to infection with these intracellular mycobacterial pathogens. In this study, a multi-omics integrative approach was applied with functional genomics and GWAS data sets across the two primary hosts (Bos taurus and Homo sapiens) and both pathogens (M. bovis and M. tuberculosis). Four different experimental infection groups were used: 1) bAM infected with M. bovis, 2) bAM infected with M. tuberculosis, 3) hAM infected with M. tuberculosis, and 4) human monocyte-derived macrophages (hMDM) infected with M. tuberculosis. RNA-seq data from these experiments 24 h post-infection (24 hpi) was analysed using three computational pipelines: 1) differentially expressed genes, 2) differential gene expression interaction networks, and 3) combined pathway analysis. The results were integrated with high-resolution bovine and human GWAS data sets to detect novel quantitative trait loci (QTLs) for resistance to mycobacterial infection and resilience to disease. This revealed common and unique response macrophage pathways for both pathogens and identified 32 genes (12 bovine and 20 human) significantly enriched for SNPs associated with disease resistance, the majority of which encode key components of the NF-κB signalling pathway and that also drive formation of the granuloma.

Inhaled aerosol viral-vectored vaccines against tuberculosis

Bacille Calmette-Guérin (BCG) remains the sole licensed vaccine against tuberculosis (TB), despite its variable efficacy in protecting against pulmonary TB. The development of effective TB vaccines faces significant challenges, marked by the absence of validated correlates of protection and predictive animal models. Strategic approaches to enhance TB vaccines and augment BCG efficacy include utilising prime-boost strategies with viral-vectored vaccines and exploring innovative delivery techniques, such as mucosal vaccine administration. Viral vectors offer numerous advantages, including the capacity to accommodate genes encoding extensive antigenic fragments and the induction of robust immune responses. Aerosol delivery aligns with the route of Mycobacterium tuberculosis infection and holds the potential to enhance protective mucosal immunity. Aerosolised viral-vectored vaccines overcome anti-vector immunity, facilitating repeated aerosol deliveries.

Lung type 3 innate lymphoid cells respond early following Mycobacterium tuberculosis infection

Tuberculosis is the leading cause of death due to an infectious disease worldwide. Innate lymphoid type 3 cells (ILC3s) mediate early protection during Mycobacterium tuberculosis (Mtb) infection. However, the early signaling mechanisms that govern ILC3 activation or recruitment within the lung during Mtb infection are unclear. scRNA-seq analysis of Mtb-infected mouse lung innate lymphoid cells (ILCs) has revealed the presence of different clusters of ILC populations, suggesting heterogeneity. Using mouse models, we show that during Mtb infection, interleukin-1 receptor (IL-1R) signaling on epithelial cells drives ILC3 expansion and regulates ILC3 accumulation in the lung. Furthermore, our data revealed that C-X-C motif chemokine receptor 5 (CXCR5) signaling plays a crucial role in ILC3 recruitment from periphery during Mtb infection. Our study thus establishes the early responses that drive ILC3 accumulation during Mtb infection and points to ILC3s as a potential vaccine target.

IMPORTANCE

Tuberculosis is a leading cause of death due to a single infectious agent accounting for 1.6 million deaths each year. In our study, we determined the role of type 3 innate lymphoid cells in early immune events necessary for achieving protection during Mtb infection. Our study reveals distinct clusters of ILC2, ILC3, and ILC3/ILC1-like cells in Mtb infection. Moreover, our study reveal that IL-1R signaling on lung type 2 epithelial cells plays a key role in lung ILC3 accumulation during Mtb infection. CXCR5 on ILC3s is involved in ILC3 homing from periphery during Mtb infection. Thus, our study provides novel insights into the early immune mechanisms governed by innate lymphoid cells that can be targeted for potential vaccine-induced protection.

The uncharted territory of host-pathogen interaction in tuberculosis

Mycobacterium tuberculosis (M.tb) effectively manipulates the host processes to establish the deadly respiratory disease, Tuberculosis (TB). M.tb has developed key mechanisms to disrupt the host cell health to combat immune responses and replicate efficaciously. M.tb antigens such as ESAT-6, 19kDa lipoprotein, Hip1, and Hsp70 destroy the integrity of cell organelles (Mitochondria, Endoplasmic Reticulum, Nucleus, Phagosomes) or delay innate/adaptive cell responses. This is followed by the induction of cellular stress responses in the host. Such cells can either undergo various cell death processes such as apoptosis or necrosis, or mount effective immune responses to clear the invading pathogen. Further, to combat the infection progression, the host secretes extracellular vesicles such as exosomes to initiate immune signaling. The exosomes can contain M.tb as well as host cell-derived peptides that can act as a double-edged sword in the immune signaling event. The host-symbiont microbiota produces various metabolites that are beneficial for maintaining healthy tissue microenvironment. In juxtaposition to the above-mentioned mechanisms, M.tb dysregulates the gut and respiratory microbiome to support its replication and dissemination process. The above-mentioned interconnected host cellular processes of Immunometabolism, Cellular stress, Host Microbiome, and Extracellular vesicles are less explored in the realm of exploration of novel Host-directed therapies for TB. Therefore, this review highlights the intertwined host cellular processes to control M.tb survival and showcases the important factors that can be targeted for designing efficacious therapy.

Immune mechanisms of granuloma formation in sarcoidosis and tuberculosis

Sarcoidosis is a complex immune-mediated disease characterized by clusters of immune cells called granulomas. Despite major steps in understanding the cause of this disease, many questions remain. In this Review, we perform a mechanistic interrogation of the immune activities that contribute to granuloma formation in sarcoidosis and compare these processes with its closest mimic, tuberculosis, highlighting shared and divergent immune activities. We examine how Mycobacterium tuberculosis is sensed by the immune system; how the granuloma is initiated, formed, and perpetuated in tuberculosis compared with sarcoidosis; and the role of major innate and adaptive immune cells in shaping these processes. Finally, we draw these findings together around several recent high-resolution studies of the granuloma in situ that utilized the latest advances in single-cell technology combined with spatial methods to analyze plausible disease mechanisms. We conclude with an overall view of granuloma formation in sarcoidosis.

Immune Responses in Lung Granulomas during Mtb/HIV Co-Infection: Implications for Pathogenesis and Therapy

HIV and TB are the cause of significant worldwide mortality and pose a grave danger to the global public health. TB is the leading cause of death in HIV-infected persons, with one in four deaths attributable to TB. While the majority of healthy individuals infected with M. tuberculosis (Mtb) are able to control the infection, co-infection with HIV increases the risk of TB infection progressing to TB disease by over 20-fold. While antiretroviral therapy (ART), the cornerstone of HIV care, decreases the incidence of TB in HIV-uninfected people, this remains 4- to 7-fold higher after ART in HIV-co-infected individuals in TB-endemic settings, regardless of the duration of therapy. Thus, the immune control of Mtb infection in Mtb/HIV-co-infected individuals is not fully restored by ART. We do not fully understand the reasons why Mtb/HIV-co-infected individuals maintain a high susceptibility to the reactivation of LTBI, despite an effective viral control by ART. A deep understanding of the molecular mechanisms that govern HIV-induced reactivation of TB is essential to develop improved treatments and vaccines for the Mtb/HIV-co-infected population. We discuss potential strategies for the mitigation of the observed chronic immune activation in combination with both anti-TB and anti-retroviral approaches.

Bladder Mucosal Cystitis Cystica Lesions Are Tertiary Lymphoid Tissues That Correlate With Recurrent Urinary Tract Infection Frequency in Postmenopausal Women

PURPOSE

We identify correlates and clinical outcomes of cystitis cystica, a poorly understood chronic inflammatory bladder change, in women with recurrent urinary tract infections.

MATERIALS AND METHODS

A retrospective, observational cohort of women with recurrent urinary tract infections who underwent cystoscopy (n=138) from 2015 to 2018 were identified using electronic medical records. Cystitis cystica status was abstracted from cystoscopy reports and correlations were identified by logistic regression. Urinary tract infection-free survival time associated with cystitis cystica was evaluated by Cox proportional hazards regression. Exact logistic regression was used to identify factors associated with changes to cystitis cystica lesions on repeat cystoscopy. Biopsies of cystitis cystica lesions were examined by routine histology and immunofluorescence.

RESULTS

Fifty-three patients (38%) had cystitis cystica on cystoscopy. Cystitis cystica was associated with postmenopausal status (OR: 5.53, 95% CI: 1.39-37.21), pelvic floor myofascial pain (6.82, 1.78-45.04), having ≥4 urinary tract infections in the past year (2.28, 1.04-5.09), and a shorter time to next urinary tract infection (HR: 1.54, 95% CI: 1.01-2.35). Forty-two patients (82%) demonstrated improvement or resolution of lesions. Ten/11 (91%) biopsied cystitis cystica lesions were tertiary lymphoid tissue with germinal centers and resembled follicular cystitis.

CONCLUSIONS

Cystitis cystica lesions were associated with postmenopausal status, pelvic floor myofascial pain, and number of urinary tract infections in the prior year and predicted worse recurrent urinary tract infection outcomes. Cystitis cystica lesions are tertiary lymphoid tissue/follicular cystitis that may improve or resolve over time with treatment. Identifying cystitis cystica in recurrent urinary tract infection patients may be useful in informing future urinary tract infection risk and tailoring appropriate treatment strategies.

B cells promote granulomatous inflammation during chronic Mycobacterium tuberculosis infection in mice

The current study reveals that in chronic TB, the B cell-deficient μMT strain, relative to wild-type (WT) C57BL/6 mice, displays in the lungs lower levels of inflammation that are associated with decreased CD4+ T cell proliferation, diminished Th1 response, and enhanced levels of interleukin (IL)-10. The latter result raises the possibility that B cells may restrict lung expression of IL-10 in chronic TB. These observations are recapitulated in WT mice depleted for B cells using anti-CD20 antibodies. IL-10 receptor (IL-10R) blockade reverses the phenotypes of decreased inflammation and attenuated CD4+ T cell responses in B cell-depleted mice. Together, these results suggest that in chronic murine TB, B cells, by virtue of their capacity to restrict expression of the anti-inflammatory and immunosuppressive IL-10 in the lungs, promote the development of a robust protective Th1 response, thereby optimizing anti-TB immunity. This vigorous Th1 immunity and restricted IL-10 expression may, however, allow the development of inflammation to a level that can be detrimental to the host. Indeed, decreased lung inflammation observed in chronically infected B cell-deficient mice, which exhibit augmented lung IL-10 levels, is associated with a survival advantage relative to WT animals. Collectively, the results reveal that in chronic murine TB, B cells play a role in modulating the protective Th1 immunity and the anti-inflammatory IL-10 response, which results in augmentation of lung inflammation that can be host-detrimental. Intriguingly, in tuberculous human lungs, conspicuous B cell aggregates are present in close proximity to tissue-damaging lesions manifesting necrosis and cavitation, suggesting the possibility that in human TB, B cells may contribute to the development of exacerbated pathology that is known to promote transmission. Since transmission is a major hindrance to TB control, investigating into whether B cells can shape the development of severe pulmonic pathological responses in tuberculous individuals is warranted.

Expression of specific HLA class II alleles is associated with an increased risk for active tuberculosis and a distinct gene expression profile

Several HLA allelic variants have been associated with protection from or susceptibility to infectious and autoimmune diseases. Here, we examined whether specific HLA alleles would be associated with different Mycobacterium tuberculosis (Mtb) infection outcomes. The HLA alleles present at the -A, -B, -C, -DPA1, -DPB1, -DQA1, -DQB1, -DRB1, and -DRB3/4/5 loci were determined in a cohort of 636 individuals with known Mtb infection outcomes from South Africa and the United States. Among these individuals, 203 were QuantiFERON (QFT) negative, and 433 were QFT positive, indicating Mtb exposure. Of these, 99 QFT positive participants either had active tuberculosis (TB) upon enrollment or were diagnosed in the past. We found that DQA1*03:01, DPB1*04:02, and DRB4*01:01 were significantly more frequent in individuals with active TB (susceptibility alleles), as judged by Odds Ratios and associated p-values, while DPB1*105:01 was associated with protection from active TB. Peripheral blood mononuclear cells (PMBCs) from a subset of individuals were stimulated with Mtb antigens, revealing individuals who express any of the three susceptibility alleles were associated with lower magnitude of responses. Furthermore, we defined a gene signature associated with individuals expressing the susceptibility alleles that was characterized by lower expression of APC-related genes. In summary, we have identified specific HLA alleles associated with susceptibility to active TB and found that the expression of these alleles was associated with a decreased Mtb-specific T cell response and a specific gene expression signature. These results will help understand individual risk factors in progressing to active TB.

Immune cell interactions in tuberculosis

Despite having been identified as the organism that causes tuberculosis in 1882, Mycobacterium tuberculosis has managed to still evade our understanding of the protective immune response against it, defying the development of an effective vaccine. Technology and novel experimental models have revealed much new knowledge, particularly with respect to the heterogeneity of the bacillus and the host response. This review focuses on certain immunological elements that have recently yielded exciting data and highlights the importance of taking a holistic approach to understanding the interaction of M. tuberculosis with the many host cells that contribute to the development of protective immunity.

Stromal structure remodeling by B lymphocytes limits T cell activation in lymph nodes of Mycobacterium tuberculosis-infected mice

An effective adaptive immune response depends on the organized architecture of secondary lymphoid organs, including the lymph nodes (LNs). While the cellular composition and microanatomy of LNs under steady state are well defined, the impact of chronic tissue inflammation on the structure and function of draining LNs is incompletely understood. Here we showed that Mycobacterium tuberculosis infection remodeled LN architecture by increasing the number and paracortical translocation of B cells. The formation of paracortical B lymphocyte and CD35+ follicular dendritic cell clusters dispersed CCL21-producing fibroblastic reticular cells and segregated pathogen-containing myeloid cells from antigen-specific CD4+ T cells. Depletion of B cells restored the chemokine and lymphoid structure and reduced bacterial burdens in LNs of the chronically infected mice. Importantly, this remodeling process impaired activation of naive CD4+ T cells in response to mycobacterial and unrelated antigens during chronic tuberculosis infection. Our studies reveal a mechanism in the regulation of LN microanatomy during inflammation and identify B cells as a critical element limiting the T cell response to persistent intracellular infection in LNs.

Pathological and protective roles of dendritic cells in Mycobacterium tuberculosis infection: Interaction between host immune responses and pathogen evasion

Dendritic cells (DCs) are principal defense components that play multifactorial roles in translating innate immune responses to adaptive immunity in Mycobacterium tuberculosis (Mtb) infections. The heterogeneous nature of DC subsets follows their altered functions by interacting with other immune cells, Mtb, and its products, enhancing host defense mechanisms or facilitating pathogen evasion. Thus, a better understanding of the immune responses initiated, promoted, and amplified or inhibited by DCs in Mtb infection is an essential step in developing anti-tuberculosis (TB) control measures, such as host-directed adjunctive therapy and anti-TB vaccines. This review summarizes the recent advances in salient DC subsets, including their phenotypic classification, cytokine profiles, functional alterations according to disease stages and environments, and consequent TB outcomes. A comprehensive overview of the role of DCs from various perspectives enables a deeper understanding of TB pathogenesis and could be useful in developing DC-based vaccines and immunotherapies.

IL-10 Overexpression After BCG Vaccination Does Not Impair Control of Mycobacterium tuberculosis Infection

Control of tuberculosis depends on the rapid expression of protective CD4+ T-cell responses in the Mycobacterium tuberculosis (Mtb)-infected lungs. We have recently shown that the immunomodulatory cytokine IL-10 acts intrinsically in CD4+ T cells and impairs their parenchymal migratory capacity, thereby preventing control of Mtb infection. Herein, we show that IL-10 overexpression does not impact the protection conferred by the established memory CD4+ T-cell response, as BCG-vaccinated mice overexpressing IL-10 only during Mtb infection display an accelerated, BCG-induced, Ag85b-specific CD4+ T-cell response and control Mtb infection. However, IL-10 inhibits the migration of recently activated ESAT-6-specific CD4+ T cells into the lung parenchyma and impairs the development of ectopic lymphoid structures associated with reduced expression of the chemokine receptors CXCR5 and CCR7. Together, our data support a role for BCG vaccination in preventing the immunosuppressive effects of IL-10 in the fast progression of Mtb infection and may provide valuable insights on the mechanisms contributing to the variable efficacy of BCG vaccination.

Role of tertiary lymphoid organs in the regulation of immune responses in the periphery

Tertiary lymphoid organs (TLOs) are collections of immune cells resembling secondary lymphoid organs (SLOs) that form in peripheral, non-lymphoid tissues in response to local chronic inflammation. While their formation mimics embryologic lymphoid organogenesis, TLOs form after birth at ectopic sites in response to local inflammation resulting in their ability to mount diverse immune responses. The structure of TLOs can vary from clusters of B and T lymphocytes to highly organized structures with B and T lymphocyte compartments, germinal centers, and lymphatic vessels (LVs) and high endothelial venules (HEVs), allowing them to generate robust immune responses at sites of tissue injury. Although our understanding of the formation and function of these structures has improved greatly over the last 30 years, their role as mediators of protective or pathologic immune responses in certain chronic inflammatory diseases remains enigmatic and may differ based on the local tissue microenvironment in which they form. In this review, we highlight the role of TLOs in the regulation of immune responses in chronic infection, chronic inflammatory and autoimmune diseases, cancer, and solid organ transplantation.

Leveraging Antibody, B Cell and Fc Receptor Interactions to Understand Heterogeneous Immune Responses in Tuberculosis

Despite over a century of research, Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), continues to kill 1.5 million people annually. Though less than 10% of infected individuals develop active disease, the specific host immune responses that lead to Mtb transmission and death, as well as those that are protective, are not yet fully defined. Recent immune correlative studies demonstrate that the spectrum of infection and disease is more heterogenous than has been classically defined. Moreover, emerging translational and animal model data attribute a diverse immune repertoire to TB outcomes. Thus, protective and detrimental immune responses to Mtb likely encompass a framework that is broader than T helper type 1 (Th1) immunity. Antibodies, Fc receptor interactions and B cells are underexplored host responses to Mtb. Poised at the interface of initial bacterial host interactions and in granulomatous lesions, antibodies and Fc receptors expressed on macrophages, neutrophils, dendritic cells, natural killer cells, T and B cells have the potential to influence local and systemic adaptive immune responses. Broadening the paradigm of protective immunity will offer new paths to improve diagnostics and vaccines to reduce the morbidity and mortality of TB.

Recombinant Human Lactoferrin Reduces Inflammation and Increases Fluoroquinolone Penetration to Primary Granulomas During Mycobacterial Infection of C57Bl/6 Mice

Infection with Mycobacterium tuberculosis (Mtb) results in the primary formation of a densely packed inflammatory foci that limits entry of therapeutic agents into pulmonary sites where organisms reside. No current therapeutic regimens exist that modulate host immune responses to permit increased drug penetration to regions of pathological damage during tuberculosis disease. Lactoferrin is a natural iron-binding protein previously demonstrated to modulate inflammation and granuloma cohesiveness, while maintaining control of pathogenic burden. Studies were designed to examine recombinant human lactoferrin (rHLF) to modulate histological progression of Mtb-induced pathology in a non-necrotic model using C57Bl/6 mice. The rHLF was oral administered at times corresponding to initiation of primary granulomatous response, or during granuloma maintenance. Treatment with rHLF demonstrated significant reduction in size of primary inflammatory foci following Mtb challenge, and permitted penetration of ofloxacin fluoroquinolone therapeutic to sites of pathological disruption where activated (foamy) macrophages reside. Increased drug penetration was accompanied by retention of endothelial cell integrity. Immunohistochemistry revealed altered patterns of M1-like and M2-like phenotypic cell localization post infectious challenge, with increased presence of M2-like markers found evenly distributed throughout regions of pulmonary inflammatory foci in rHLF-treated mice.

Early IL-10 promotes vasculature-associated CD4+ T cells unable to control Mycobacterium tuberculosis infection

Cytokine-producing CD4⁺ T cells play a crucial role in the control of Mycobacterium tuberculosis infection; however, there is a delayed appearance of effector T cells in the lungs following aerosol infection. The immunomodulatory cytokine IL-10 antagonizes control of M. tuberculosis infection through mechanisms associated with reduced CD4⁺ T cell responses. Here, we show that IL-10 overexpression only before the onset of the T cell response impaired control of M. tuberculosis growth; during chronic infection, IL-10 overexpression reduced the CD4⁺ T cell response without affecting the outcome of infection. IL-10 overexpression early during infection did not, we found, significantly impair the kinetics of CD4⁺ T cell priming and effector differentiation. However, CD4⁺ T cells primed and differentiated in an IL-10–enriched environment displayed reduced expression of CXCR3 and, because they did not migrate into the lung parenchyma, their ability to control infection was limited. Importantly, these CD4⁺ T cells maintained their vasculature phenotype and were unable to control infection, even after adoptive transfer into low IL-10 settings. Together our data support a model wherein, during M. tuberculosis infection, IL-10 acts intrinsically on T cells, impairing their parenchymal migratory capacity and ability to engage with infected phagocytic cells, thereby impeding control of infection.

Integrative Analysis of Human Macrophage Inflammatory Response Related to Mycobacterium tuberculosis Virulence

Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis, kills 1.5 to 1.7 million people every year. Macrophages are Mtb's main host cells and their inflammatory response is an essential component of the host defense against Mtb. However, Mtb is able to circumvent the macrophages' defenses by triggering an inappropriate inflammatory response. The ability of Mtb to hinder phagolysosome maturation and acidification, and to escape the phagosome into the cytosol, is closely linked to its virulence. The modulation of the host inflammatory response relies on Mtb virulence factors, but remains poorly studied. Understanding macrophage interactions with Mtb is crucial to develop strategies to control tuberculosis. The present study aims to determine the inflammatory response transcriptome and miRNome of human macrophages infected with the virulent H37Rv Mtb strain, to identify macrophage genetic networks specifically modulated by Mtb virulence. Using human macrophages infected with two different live strains of mycobacteria (live or heat-inactivated Mtb H37Rv and M. marinum), we quantified and analyzed 184 inflammatory mRNAs and 765 micro(mi)RNAs. Transcripts and miRNAs differently modulated by H37Rv in comparison with the two other conditions were analyzed using in silico approaches. We identified 30 host inflammatory response genes and 37 miRNAs specific for H37Rv virulence, and highlight evidence suggesting that Mtb intracellular-linked virulence depends on the inhibition of IL-1β-dependent pro-inflammatory response, the repression of apoptosis and the delay of the recruitment and activation of adaptive immune cells. Our findings provide new potential targets for the development of macrophage-based therapeutic strategies against TB.

B-Cells and Antibodies as Contributors to Effector Immune Responses in Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is still a major threat to mankind, urgently requiring improved vaccination and therapeutic strategies to reduce TB-disease burden. Most present vaccination strategies mainly aim to induce cell-mediated immunity (CMI), yet a series of independent studies has shown that B-cells and antibodies (Abs) may contribute significantly to reduce the mycobacterial burden. Although early studies using B-cell knock out animals did not support a major role for B-cells, more recent studies have provided new evidence that B-cells and Abs can contribute significantly to host defense against Mtb. B-cells and Abs exist in many different functional subsets, each equipped with unique functional properties. In this review, we will summarize current evidence on the contribution of B-cells and Abs to immunity toward Mtb, their potential utility as biomarkers, and their functional contribution to Mtb control.

Mycobacterium tuberculosis HN878 Infection Induces Human-Like B-Cell Follicles in Mice

Specific spatial organization of granulomas within the lungs is crucial for protective anti-tuberculosis (TB) immune responses. However, only large animal models such as macaques are thought to reproduce the morphological hallmarks of human TB granulomas. In this study, we show that infection of mice with clinical "hypervirulent" Mycobacterium tuberculosis (Mtb) HN878 induces human-like granulomas composed of bacilli-loaded macrophages surrounded by lymphocytes and organized localization of germinal centers and B-cell follicles. Infection with laboratory-adapted Mtb H37Rv resulted in granulomas that are characterized by unorganized clusters of macrophages scattered between lymphocytes. An in-depth exploration of the functions of B cells within these follicles suggested diverse roles and the activation of signaling pathways associated with antigen presentation and immune cell recruitment. These findings support the use of clinical Mtb HN878 strain for infection in mice as an appropriate model to study immune parameters associated with human TB granulomas.

T resident helper cells promote humoral responses in the lung

Influenza is a deadly and costly infectious disease, even during flu seasons when an effective vaccine has been developed. To improve vaccines against respiratory viruses, a better understanding of the immune response at the site of infection is crucial. After influenza infection, clonally expanded T cells take up permanent residence in the lung, poised to rapidly respond to subsequent infection. Here, we characterized the dynamics and transcriptional regulation of lung-resident CD4⁺ T cells during influenza infection and identified a long-lived, Bcl6-dependent population that we have termed T resident helper (T_RH) cells. T_RH cells arise in the lung independently of lymph node T follicular helper cells but are dependent on B cells, with which they tightly colocalize in inducible bronchus-associated lymphoid tissue (iBALT). Deletion of Bcl6 in CD4⁺ T cells before heterotypic challenge infection resulted in redistribution of CD4⁺ T cells outside of iBALT areas and impaired local antibody production. These results highlight iBALT as a homeostatic niche for T_RH cells and advocate for vaccination strategies that induce T_RH cells in the lung.

Tertiary Lymphoid Organs: A Primer for Otolaryngologists

OBJECTIVES/HYPOTHESIS

Lymphoid neogenesis or the development of organised, de novo lymphoid structures has been described increasingly in chronically inflamed tissues. The presence of tertiary lymphoid organs (TLOs) has already been demonstrated to result in significant consequences for disease pathology, severity, prognosis and patient outcomes. Whilst the wider medical community has embraced TLOs as important markers of disease and potential therapeutic targets, the otolaryngology field has only begun turning to these entities in an academic capacity. This review aims to outline the role of tertiary lymphoid organs in disease and summarise key early findings in the ENT field. We also an overview of TLOs, their developmental process and clinicopathological implications.

STUDY DESIGN

Literature review.

METHODS

A literature search for all relevant peer-reviewed publications pertaining to TLOs and ENT diseases. Search was conducted using PubMed, Embase and CINAHL databases.

RESULTS

A total of 24 studies were identified relevant to the topic. The majority of TLO research in ENT fell into the areas of oral squamous cell carcinoma (SCC) and chronic rhinosinusitis (CRS).

CONCLUSIONS

Early research into both oral SCC and CRS suggests that TLOs have significant roles within ear, nose and throat (ENT) diseases. At this point in time, however, TLOs remain somewhat a mystery amongst otolaryngologists. As information in this field increases, we may develop a better understanding of how lymphoid neogenesis can influence disease outcomes amongst our patients and, ultimately, how they can be utilised in an immunotherapeutic manner. Laryngoscope, 131:1697-1703, 2021.

Inducible Bronchus-Associated Lymphoid Tissue (iBALT) Attenuates Pulmonary Pathology in a Mouse Model of Allergic Airway Disease

Inducible Bronchus Associated Lymphoid Tissue (iBALT) is an ectopic lymphoid tissue associated with severe forms of chronic lung diseases, including chronic obstructive pulmonary disease, rheumatoid lung disease, hypersensitivity pneumonitis and asthma, suggesting that iBALT may exacerbate these clinical conditions. However, despite the link between pulmonary pathology and iBALT formation, the role of iBALT in pathogenesis remains unknown. Here we tested whether the presence of iBALT in the lung prior to sensitization and challenge with a pulmonary allergen altered the biological outcome of disease. We found that the presence of iBALT did not exacerbate Th2 responses to pulmonary sensitization with ovalbumin. Instead, we found that mice with iBALT exhibited delayed Th2 accumulation in the lung, reduced eosinophil recruitment, reduced goblet cell hyperplasia and reduced mucus production. The presence of iBALT did not alter Th2 priming, but instead delayed the accumulation of Th2 cells in the lung following challenge and altered the spatial distribution of T cells in the lung. These results suggest that the formation of iBALT and sequestration of effector T cells in the context of chronic pulmonary inflammation may be a mechanism by which the immune system attenuates pulmonary inflammation and prevents excessive pathology.

Biological mechanisms of ectopic lymphoid structure formation and their pathophysiological significance

Ectopic lymphoid structures (ELS) or tertiary lymphoid organs are structures with the organization similar to the one of secondary lymphoid organs, formed in non-lymphoid tissues. They are considered to be an important site for the lymphocytic physiological and pathological role in conditions such are chronic infections, autoimmune diseases, cancer, and allograft rejection. Although similar to the secondary lymphoid tissues, the initiation of ELS formation is not preprogramed and requires chronic inflammation, expression of homeostatic chemokines, and lymphotoxin beta receptor activation. Importantly, while ELS formation may be considered beneficiary in antimicrobial and antitumor immunity, the persistence of these active lymphoid structures within the tissue increase the chance for development of autoimmunity and lymphoma. This paper is providing an overview of biological mechanisms involved in ELS formation, as well as the overview of the pathophysiological role of these structures. In addition, the paper discusses the possibility to therapeutically target ELS formation, bearing in mind their bivalent nature and role in different pathophysiological conditions.

Increased male susceptibility to Mycobacterium tuberculosis infection is associated with smaller B cell follicles in the lungs

Tuberculosis prevalence is significantly higher among men than women. We have previously revealed an increased susceptibility of male C57BL/6 mice towards Mycobacterium tuberculosis (Mtb) H37Rv. In the current study, we confirm the male bias for infection with the Beijing strain HN878. Males succumbed to HN878 infection significantly earlier than females. In both models, premature death of males was associated with smaller B cell follicles in the lungs. Analysis of homeostatic chemokines and their receptors revealed differences between H37Rv and HN878 infected animals, indicating different immune requirements for follicle formation in both models. However, expression of IL-23, which is involved in long-term containment of Mtb and lymphoid follicle formation, was reduced in male compared to female lungs in both models. Our study reveals sex differences in the formation of B cell follicles in the Mtb infected lung and we propose that impaired follicle formation is responsible for accelerated disease progression in males.

Friend or Foe: The Protective and Pathological Roles of Inducible Bronchus-Associated Lymphoid Tissue in Pulmonary Diseases

Inducible bronchus-associated lymphoid tissue (iBALT) is a tertiary lymphoid structure that resembles secondary lymphoid organs. iBALT is induced in the lung in response to Ag exposure. In some cases, such as infection with Mycobacterium tuberculosis, the formation of iBALT structure is indicative of an effective protective immune response. However, with persistent exposure to Ags during chronic inflammation, allergy, or autoimmune diseases, iBALT may be associated with exacerbation of inflammation. iBALT is characterized by well-organized T and B areas enmeshed with conventional dendritic cells, follicular dendritic cells, and stromal cells, usually located surrounding airways or blood vessels. Several of the molecular signals and cellular contributors that mediate formation of iBALT structures have been recently identified. This review will outline the recent findings associated with the formation and maintenance of iBALT and their contributions toward a protective or pathogenic function in pulmonary disease outcome.

Mycobacterium indicus pranii Induced Memory T-Cells in Lung Airways Are Sentinels for Improved Protection Against M.tb Infection

The lungs are the most vulnerable site for air-borne infections. Immunologic compartmentalization of the lungs into airway lumen and interstitium has paved the way to determine the immune status of the site of pathogen entry, which is crucial for the outcome of any air-borne infections. Vaccination via the nasal route with Mycobacterium indicus pranii (MIP), a prospective candidate vaccine against tuberculosis (TB), has been reported to confer superior protection as compared to the subcutaneous (s.c.) route in small-animal models of TB. However, the immune mechanism remains only partly understood. Here, we showed that intranasal (i.n.) immunization of mice with MIP resulted in a significant recruitment of CD4⁺ and CD8⁺ T-cells expressing activation markers in the lung airway lumen. A strong memory T-cell response was observed in the lung airway lumen after i.n. MIP vaccination, compared with s.c. vaccination. The recruitment of these T-cells was regulated primarily by CXCR3–CXCL11 axis in “MIP i.n.” group. MIP-primed T-cells in the lung airway lumen effectively transferred protective immunity into naïve mice against Mycobacterium tuberculosis (M.tb) infection and helped reducing the pulmonary bacterial burden. These signatures of protective immune response were virtually absent or very low in unimmunized and subcutaneously immunized mice, respectively, before and after M.tb challenge. Our study provides mechanistic insights for MIP-elicited protective response against M.tb infection.

Protective role of B cells in sterile particulate-induced lung injury

Susceptibility to chronic beryllium (Be) disease is linked to HLA-DP molecules possessing a glutamic acid at the 69th position of the β-chain (βGlu69), with the most prevalent βGlu69-containing molecule being HLA-DP2. We have previously shown that HLA-DP2 transgenic (Tg) mice exposed to Be oxide (BeO) develop mononuclear infiltrates in a peribronchovascular distribution and a beryllium-specific, HLA-DP2-restricted CD4+ T cell response. In addition to T cells, B cells constituted a major portion of infiltrated leukocytes in the lung of BeO-exposed HLA-DP2 Tg mice and sequester BeO particles within ectopic lymphoid aggregates and granulomas. B cell depletion was associated with a loss of lymphoid aggregates and granulomas as well as a significant increase in lung injury in BeO-exposed mice. The protective role of B cells was innate in origin, and BeO-induced B cell recruitment to the lung was dependent on MyD88 signaling. Similar to BeO-exposed HLA-DP2 mice, B cells also accumulate in the lungs of CBD subjects, located at the periphery and surrounding the granuloma. Overall, our data suggest a novel modulatory role for B cells in the protection of the lung against sterile particulate exposure, with B cell recruitment to the inflamed lung occurring in an antigen-independent and MyD88-dependent manner.

B lymphocytes in anti-mycobacterial immune responses: Pathogenesis or protection?

The role of B cells and antibodies in tuberculosis (TB) immunity, protection and pathogenesis remain contradictory. The presence of organized B cell follicles close to active TB lesions in the lung tissue raises the question about the role of these cells in local host-pathogen interactions. In this short review, we summarize the state of our knowledge concerning phenotypes of B cells populating tuberculous lungs, their secretory activity, interactions with other immune cells and possible involvement in protective vs. pathogenic TB immunity.

The increased protection and pathology in Mycobacterium tuberculosis-infected IL-27R-alpha-deficient mice is supported by IL-17A and is associated with the IL-17A-induced expansion of multifunctional T cells

During Mycobacterium tuberculosis (Mtb) infection, mice lacking the IL-27R exhibit lower bacterial burdens but develop an immunopathological sequelae in comparison to wild-type mice. We here show that this phenotype correlates with an enhanced recruitment of antigen-specific CCR6⁺ CD4⁺ T cells and an increased frequency of IL-17A-producing CD4⁺ T cells. By comparing the outcome of Mtb infection in C57BL/6, IL-27R-deficient and IL-27R/IL-17A-double deficient mice, we observed that both the increased protection and elevated immunopathology are supported by IL-17A. Whereas IL-17A neither impacts the development of Tr1 cells nor the expression of PD1 and KLRG1 on T cells in IL-27R-deficient mice during infection, it regulates the presence of multifunctional T-cells in the lungs, co-expressing IFN-γ, IL-2 and TNF. Eventually, IL-17A supports Cxcl9, Cxcl10 and Cxcl13 expression and the granulomatous response in the lungs of infected IL-27R-deficient mice. Taken together, IL-17A contributes to protection in Mtb-infected IL-27R-deficient mice probably through a chemokine-mediated recruitment and strategic positioning of multifunctional T cells in granulomas. As IL-27 limits optimal antimycobacterial protection by inhibiting IL-17A production, blocking of IL-27R-mediated signaling may represent a strategy for improving vaccination and host-directed therapy in tuberculosis. However, because IL-27 also prevents IL-17A-mediated immunopathology, such intervention has to be tightly controlled.

GI-19007, a Novel Saccharomyces cerevisiae-Based Therapeutic Vaccine against Tuberculosis

As yet, very few vaccine candidates with activity in animals against Mycobacterium tuberculosis infection have been tested as therapeutic postexposure vaccines. We recently described two pools of mycobacterial proteins with this activity, and here we describe further studies in which four of these proteins (Rv1738, Rv2032, Rv3130, and Rv3841) were generated as a fusion polypeptide and then delivered in a novel yeast-based platform (Tarmogen) which itself has immunostimulatory properties, including activation of Toll-like receptors. This platform can deliver antigens into both the class I and class II antigen presentation pathways and stimulate strong Th1 and Th17 responses. In mice this fusion vaccine, designated GI-19007, was immunogenic and elicited strong gamma interferon (IFN-γ) and interleukin-17 (IL-17) responses; despite this, they displayed minimal prophylactic activity in mice that were subsequently infected with a virulent clinical strain. In contrast, in a therapeutic model in the guinea pig, GI-19007 significantly reduced the lung bacterial load and reduced lung pathology, particularly in terms of secondary lesion development, while significantly improving survival in one-third of these animals. In further studies in which guinea pigs were vaccinated with BCG before challenge, therapeutic vaccination with GI-19007 initially improved survival versus that of animals given BCG alone, although this protective effect was gradually lost at around 400 days after challenge. Given its apparent ability to substantially limit bacterial dissemination within and from the lungs, GI-19007 potentially can be used to limit lung damage as well as facilitating chemotherapeutic regimens in infected individuals.

A Novel In Vitro Human Granuloma Model of Sarcoidosis and Latent Tuberculosis Infection

Many aspects of pathogenic granuloma formation are poorly understood, requiring new relevant laboratory models that represent the complexity (genetics and diversity) of human disease. To address this need, we developed an in vitro model of granuloma formation using human peripheral blood mononuclear cells (PBMCs) derived from patients with active sarcoidosis, latent tuberculosis (TB) infection (LTBI), or normal healthy control subjects. PBMCs were incubated for 7 days with uncoated polystyrene beads or beads coated with purified protein derivative (PPD) or human serum albumin. In response to PPD-coated beads, PBMCs from donors with sarcoidosis and LTBI formed robust multicellular aggregates resembling granulomas, displaying a typical T-helper cell type 1 immune response, as assessed by cytokine analyses. In contrast, minimal PBMC aggregation occurred when control PBMCs were incubated with PPD-coated beads, whereas the response to uncoated beads was negligible in all groups. Sarcoidosis PBMCs responded to human serum albumin-coated beads with modest cellular aggregation and inflammatory cytokine release. Whereas the granuloma-like aggregates formed in response to PPD-coated beads were similar for sarcoidosis and LTBI, molecular profiles differed significantly. mRNA expression patterns revealed distinct pathways engaged in early granuloma formation in sarcoidosis and LTBI, and they resemble molecular patterns reported in diseased human tissues. This novel in vitro human granuloma model is proposed as a tool to investigate mechanisms of early granuloma formation and for preclinical drug discovery research of human granulomatous disorders. Clinical trial registered with www.clinicaltrials.gov (NCT01857401).

Interleukin-17 limits hypoxia-inducible factor 1α and development of hypoxic granulomas during tuberculosis

Mycobacterium tuberculosis (Mtb) is a global health threat, compounded by the emergence of drug-resistant strains. A hallmark of pulmonary tuberculosis (TB) is the formation of hypoxic necrotic granulomas, which upon disintegration, release infectious Mtb. Furthermore, hypoxic necrotic granulomas are associated with increased disease severity and provide a niche for drug-resistant Mtb. However, the host immune responses that promote the development of hypoxic TB granulomas are not well described. Using a necrotic Mtb mouse model, we show that loss of Mtb virulence factors, such as phenolic glycolipids, decreases the production of the proinflammatory cytokine IL-17 (also referred to as IL-17A). IL-17 production negatively regulates the development of hypoxic TB granulomas by limiting the expression of the transcription factor hypoxia-inducible factor 1α (HIF1α). In human TB patients, HIF1α mRNA expression is increased. Through genotyping and association analyses in human samples, we identified a link between the single nucleotide polymorphism rs2275913 in the IL-17 promoter (-197G/G), which is associated with decreased IL-17 production upon stimulation with Mtb cell wall. Together, our data highlight a potentially novel role for IL-17 in limiting the development of hypoxic necrotic granulomas and reducing disease severity in TB.

A novel nanoemulsion vaccine induces mucosal Interleukin-17 responses and confers protection upon Mycobacterium tuberculosis challenge in mice

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) is contracted via aerosol infection, typically affecting the lungs. Mycobacterium bovis bacillus Calmette-Guerin (BCG) is the only licensed vaccine and has variable efficacy in protecting against pulmonary TB. Additionally, chemotherapy is associated with low compliance contributing to development of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb. Thus, there is an urgent need for the design of more effective vaccines against TB. Experimental vaccines delivered through the mucosal route induce robust T helper type 17 (Th17)/ Interleukin (IL) -17 responses and provide superior protection against Mtb infection. Thus, the development of safe mucosal adjuvants for human use is critical. In this study, we demonstrate that nanoemulsion (NE)-based adjuvants when delivered intranasally along with Mtb specific immunodominant antigens (NE-TB vaccine) induce potent mucosal IL-17T-cell responses. Additionally, the NE-TB vaccine confers significant protection against Mtb infection, and when delivered along with BCG, is associated with decreased disease severity. These findings strongly support the development of a NE-TB vaccine as a novel, safe and effective, first-of-kind IL-17 inducing mucosal vaccine for potential use in humans.

A review of computational and mathematical modeling contributions to our understanding of Mycobacterium tuberculosis within-host infection and treatment

Tuberculosis (TB) is an ancient and deadly disease characterized by complex host-pathogen dynamics playing out over multiple time and length scales and physiological compartments. Computational modeling can be used to integrate various types of experimental data and suggest new hypotheses, mechanisms, and therapeutic approaches to TB. Here, we offer a first-time comprehensive review of work on within-host TB models that describe the immune response of the host to infection, including the formation of lung granulomas. The models include systems of ordinary and partial differential equations and agent-based models as well as hybrid and multi-scale models that are combinations of these. Many aspects of M. tuberculosis infection, including host dynamics in the lung (typical site of infection for TB), granuloma formation, roles of cytokine and chemokine dynamics, and bacterial nutrient availability have been explored. Finally, we survey applications of these within-host models to TB therapy and prevention and suggest future directions to impact this global disease.

Tertiary lymphoid organs in systemic autoimmune diseases: pathogenic or protective?

Tertiary lymphoid organs are found at sites of chronic inflammation in autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. These organized accumulations of T and B cells resemble secondary lymphoid organs and generate autoreactive effector cells. However, whether they contribute to disease pathogenesis or have protective functions is unclear. Here, we discuss how tertiary lymphoid organs can generate potentially pathogenic cells but may also limit the extent of the response and damage in autoimmune disease.

Cytokines and Chemokines in Mycobacterium tuberculosis Infection

Chemokines and cytokines are critical for initiating and coordinating the organized and sequential recruitment and activation of cells into Mycobacterium tuberculosis-infected lungs. Correct mononuclear cellular recruitment and localization are essential to ensure control of bacterial growth without the development of diffuse and damaging granulocytic inflammation. An important block to our understanding of TB pathogenesis lies in dissecting the critical aspects of the cytokine/chemokine interplay in light of the conditional role these molecules play throughout infection and disease development. Much of the data highlighted in this review appears at first glance to be contradictory, but it is the balance between the cytokines and chemokines that is critical, and the "goldilocks" (not too much and not too little) phenomenon is paramount in any discussion of the role of these molecules in TB. Determination of how the key chemokines/cytokines and their receptors are balanced and how the loss of that balance can promote disease is vital to understanding TB pathogenesis and to identifying novel therapies for effective eradication of this disease.

Understanding the pathophysiology of the human TB lung granuloma using in vitro granuloma models

Tuberculosis remains a major human health threat that infects one in three individuals worldwide. Infection with Mycobacterium tuberculosis is a standoff between host and bacteria in the formation of a granuloma. This review will introduce a variety of bacterial and host factors that impact individual granuloma fates. The authors describe advances in the development of in vitro granuloma models, current evidence surrounding infection and granuloma development, and the applicability of existing in vitro models in the study of human disease. In vitro models of infection help improve our understanding of pathophysiology and allow for the discovery of other potential models of study.

Inducible Bronchus-Associated Lymphoid Tissue: Taming Inflammation in the Lung

Following pulmonary inflammation, leukocytes that infiltrate the lung often assemble into structures known as inducible Bronchus-Associated Lymphoid Tissue (iBALT). Like conventional lymphoid organs, areas of iBALT have segregated B and T cell areas, specialized stromal cells, high endothelial venules, and lymphatic vessels. After inflammation is resolved, iBALT is maintained for months, independently of inflammation. Once iBALT is formed, it participates in immune responses to pulmonary antigens, including those that are unrelated to the iBALT-initiating antigen, and often alters the clinical course of disease. However, the mechanisms that govern immune responses in iBALT and determine how iBALT impacts local and systemic immunity are poorly understood. Here, we review our current understanding of iBALT formation and discuss how iBALT participates in pulmonary immunity.

Discriminative expression of whole blood genes in HIV patients with latent and active TB in Ethiopia

BACKGROUND

Transcriptomic host biomarkers could assist in developing effective diagnostics, vaccines and therapeutics for tuberculosis (TB). However, different biomarkers may be discriminatory in different populations depending on the host and bacillary genetics and HIV infection, and need to be addressed.

METHODS

The expression levels of 45 genes that are known to be involved in or affected by TB pathogenesis were analyzed using dual color Reverse Transcriptase Multiplex Ligation-dependent Probe Amplification (dcRT-MLPA) assay in whole blood of 106 HIV positive individuals including active TB patients (TB(+)HIV(+), n = 29), and non TB patients that are tuberculin skin test positive (TST+) (TST(+)HIV(+), n = 26), or TST negative (TST(-)HIV(+), n = 51).

RESULTS

Between the two clinical groups (TB(+)HIV(+) vs. TST(-)HIV(+)) 8 genes were differently expressed (CCL19, CD14, CD8A, FPR1, IL7R, CCL22, TNFRSF1A, and FCGR1A); between TB(+)HIV(+) vs. TST(+)HIV(+), 6 genes (CD14, IL7R, TIMP2, CCL22, TNFRSF1A, and FCGR1A) were differently expressed. Since no difference in gene expression was revealed between TST(+)HIV(+) vs. TST(-)HIV(+), we clustered both the TST(+)HIV(+) and TST(-)HIV(+) individuals as one group (TST(+/-)HIV(+)) and compared gene expression with TB(+)HIV(+) patients. Thus, the results revealed that the levels of five genes (CD8A, TIMP2, CCL22, FCGR1A and TNFRSF1A) were the most accurate single gene markers for differentiation between TB(+)HIV(+) and TST(+/-)HIV(+), with AUCs of 0.71, 0.71, 0.79, 0.83 and 0.73, respectively. However, the combination of two genes (CCL22 + FCGR1A) and FCGR1A alone were the most accurate marker for differentiation between the two groups (TB(+)HIV(+) and TST(+/-)HIV(+)) with AUC of 0.85 and 0.83, respectively.

CONCLUSIONS

We showed that five genes (CD8A, TIMP2, CCL22, FCGR1A and TNFRSF1A), specifically FCGR1A and CCL22 have the potential to discriminate active TB from non-active TB in HIV patients in Ethiopia and could be used to improve diagnostic tools for active TB in HIV patients, and to understand the pathogenesis of TB/HIV coinfection.

Effects of B Cell Depletion on Early Mycobacterium tuberculosis Infection in Cynomolgus Macaques

Although recent studies in mice have shown that components of B cell and humoral immunity can modulate the immune responses against Mycobacterium tuberculosis, the roles of these components in human and nonhuman primate infections are unknown. The cynomolgus macaque (Macaca fascicularis) model of M. tuberculosis infection closely mirrors the infection outcomes and pathology in human tuberculosis (TB). The present study used rituximab, an anti-CD20 antibody, to deplete B cells in M. tuberculosis-infected macaques to examine the contribution of B cells and humoral immunity to the control of TB in nonhuman primates during the acute phase of infection. While there was no difference in the overall pathology, disease profession, and clinical outcome between the rituximab-treated and untreated macaques in acute infection, analyzing individual granulomas revealed that B cell depletion resulted in altered local T cell and cytokine responses, increased bacterial burden, and lower levels of inflammation. There were elevated frequencies of T cells producing interleukin-2 (IL-2), IL-10, and IL-17 and decreased IL-6 and IL-10 levels within granulomas from B cell-depleted animals. The effects of B cell depletion varied among granulomas in an individual animal, as well as among animals, underscoring the previously reported heterogeneity of local immunologic characteristics of tuberculous granulomas in nonhuman primates. Taken together, our data clearly showed that B cells can modulate the local granulomatous response in M. tuberculosis-infected macaques during acute infection. The impact of these alterations on disease progression and outcome in the chronic phase remains to be determined.

Lactoferrin: A Modulator for Immunity against Tuberculosis Related Granulomatous Pathology

There is great need for a therapeutic that would limit tuberculosis related pathology and thus curtail spread of disease between individuals by establishing a "firebreak" to slow transmission. A promising avenue to increase current therapeutic efficacy may be through incorporation of adjunct components that slow or stop development of aggressive destructive pulmonary pathology. Lactoferrin, an iron-binding glycoprotein found in mucosal secretions and granules of neutrophils, is just such a potential adjunct therapeutic agent. The focus of this review is to explore the utility of lactoferrin to serve as a therapeutic tool to investigate "disruption" of the mycobacterial granuloma. Proposed concepts for mechanisms underlying lactoferrin efficacy to control immunopathology are supported by data generated based on in vivo models using nonpathogenic trehalose 6,6'-dimycolate (TDM, cord factor).

Infection with Mycobacterium tuberculosis induces the Warburg effect in mouse lungs

To elucidate the little-known bioenergetic pathways of host immune cells in tuberculosis, a granulomatous disease caused by the intracellular pathogen Mycobacterium tuberculosis, we characterized infected murine lung tissue by transcriptomic profiling and confocal imaging. Transcriptomic analysis revealed changes of host energy metabolism during the course of infection that are characterized by upregulation of key glycolytic enzymes and transporters for glucose uptake, and downregulation of enzymes participating in the tricarboxylic acid cycle and oxidative phosphorylation. Consistent with elevated glycolysis, we also observed upregulation of a transporter for lactate secretion and a V type H(+) -ATPase involved in cytosolic pH homeostasis. Transcription profiling results were corroborated by immunofluorescence microscopy showing increased expression of key glycolytic enzymes in macrophages and T cells in granulomatous lesions. Moreover, we found increased mRNA and protein levels in macrophages and T cells of hypoxia inducible factor 1 alpha (HIF-1α), the regulatory subunit of HIF-1, a master transcriptional regulator. Thus, our findings suggest that immune cells predominantly utilize aerobic glycolysis in response to M. tuberculosis infection. This bioenergetic shift is similar to the Warburg effect, the metabolic signature of cancer cells. Finding immunometabolic changes during M. tuberculosis infection opens the way to new strategies for immunotherapy against tuberculosis.

Ectopic lymphoid follicles: inducible centres for generating antigen-specific immune responses within tissues

Lymphoid neogenesis is traditionally viewed as a pre‐programmed process that promotes the formation of lymphoid organs during development. Here, the spatial organization of T and B cells in lymph nodes and spleen into discrete structures regulates antigen‐specific responses and adaptive immunity following immune challenge. However, lymphoid neogenesis is also triggered by chronic or persistent inflammation. Here, ectopic (or tertiary) lymphoid organs frequently develop in inflamed tissues as a response to infection, auto‐immunity, transplantation, cancer or environmental irritants. Although these structures affect local immune responses, the contribution of these lymphoid aggregates to the underlining pathology are highly context dependent and can elicit either protective or deleterious outcomes. Here we review the cellular and molecular mechanisms responsible for ectopic lymphoid neogenesis and consider the relevance of these structures in human disease.

The onset of adaptive immunity in the mouse model of tuberculosis and the factors that compromise its expression

Mycobacterium tuberculosis (Mtb) has been evolving with its human host for over 50 000 years and is an exquisite manipulator of the human immune response. It induces both a strong inflammatory and a strong acquired immune response, and Mtb then actively regulates these responses to create an infectious lesion in the lung while maintaining a relatively ambulatory host. The CD4(+) T cell plays a critical yet contradictory role in this process by both controlling disseminated disease while promoting the development of the lesion in the lung that mediates transmission. In light of this manipulative relationship between Mtb and the human immune response, it is not surprising that our ability to vaccinate against tuberculosis (TB) has not been totally successful. To overcome the current impasse in vaccine development, we need to define the phenotype of CD4(+) T cells that mediate protection and to determine those bacterial and host factors that regulate the effective function of these cells. In this review, we describe the initiation and expression of T cells during TB as well as the fulminant inflammatory response that can compromise T-cell function and survival.

Long-Lasting Impact of Neonatal Exposure to Total Body Gamma Radiation on Secondary Lymphoid Organ Structure and Function

The acute period after total body irradiation (TBI) is associated with an increased risk of infection, principally resulting from the loss of hematopoietic stem cells, as well as disruption of mucosal epithelial barriers. Although there is a return to baseline infection control coinciding with the apparent progressive recovery of hematopoietic cell populations, late susceptibility to infection in radiation-sensitive organs such as lung and kidney is known to occur. Indeed, pulmonary infections are particularly prevalent in hematopoietic cell transplant (HCT) survivors, in both adult and pediatric patient populations. Preclinical studies investigating late outcomes from localized thoracic irradiation have indicated that the mechanisms underlying pulmonary delayed effects are multifactorial, including exacerbated and persistent production of pro-inflammatory molecules and abnormal cross-talk among parenchymal and infiltrating immune and inflammatory cell populations. However, in the context of low-dose TBI, it is not clear whether the observed exacerbated response to infection remains contingent on these same mechanisms. It is possible instead, that after systemic radiation-induced injury, the susceptibility to infection may be independently related to defects in alternative organs that are revealed only through the challenge itself; indeed, we have hypothesized that this defect may be due to radiation-induced chronic effects in the structure and function of secondary lymphoid organs (SLO). In this study, we investigated the molecular and cellular alterations in SLO (i.e., spleen, mediastinal, inguinal and mesenteric lymph nodes) after TBI, and the time points when there appears to be immune competence. Furthermore, due to the high incidence of pulmonary infections in the late post-transplantation period of bone marrow transplant survivors, particularly in children, we focused on outcomes in mice irradiated as neonates, which served as a model for a pediatric population, and used the induction of adaptive immunity against influenza virus as a functional end point. We demonstrated that, in adult animals irradiated as neonates, high endothelial venule (HEV) expansion, generation of follicular helper T cells (TFH) and formation of splenic germinal centers (GC) were rapidly and, more importantly, persistently impaired in SLO, suggesting that the early-life exposure to sublethal radiation had long-lasting effects on the induction of humoral immunity. Although the neonatal TBI did not affect the overall outcome from influenza infection in the adults at the earlier time points assessed, we believe that they nonetheless contribute significantly to the increased mortality observed at subsequent late time points. Furthermore, we speculate that the detrimental and persistent impact on the induction of CD4 T- and B-cell responses in the mediastinal lymph nodes will decrease the animals' ability to respond to other aerial pathogens. Since many of these pathogens are normally cleared by antibodies, our findings provide an explanation for the susceptibility of survivors of childhood HCT to life-threatening respiratory tract infections. These findings have implications regarding the need for increased monitoring in pediatric hematopoietic cell transplant patients, since they indicate that there are ongoing and cumulative defects in SLO, which, importantly, develop during the immediate and early postirradiation period when patients may appear immunologically competent. The identification of changes in immune-related signals may offer bioindicators of progressive dysfunction, and of potential mechanisms that could be targeted so as to reduce the risk of infection from extracellular pathogens. Furthermore, these results support the potential susceptibility of the pediatric population to infection after sublethal irradiation in the context of a nuclear or radiological event.

Immune requirements for protective Th17 recall responses to Mycobacterium tuberculosis challenge

Tuberculosis (TB) vaccine development has focused largely on targeting T helper type 1 (Th1) cells. However, despite inducing Th1 cells, the recombinant TB vaccine MVA85A failed to enhance protection against TB disease in humans. In recent years, Th17 cells have emerged as key players in vaccine-induced protection against TB. However, the exact cytokine and immune requirements that enable Th17-induced recall protection remain unclear. In this study, we have investigated the requirements for Th17 cell-induced recall protection against Mycobacterium tuberculosis (Mtb) challenge by utilizing a tractable adoptive transfer model in mice. We demonstrate that adoptive transfer of Mtb-specific Th17 cells into naive hosts, and upon Mtb challenge, results in Th17 recall responses that confer protection at levels similar to vaccination strategies. Importantly, although interleukin (IL)-23 is critical, IL-12 and IL-21 are dispensable for protective Th17 recall responses. Unexpectedly, we demonstrate that interferon-γ (IFN-γ) produced by adoptively transferred Th17 cells impairs long-lasting protective recall immunity against Mtb challenge. In contrast, CXCR5 expression is crucial for localization of Th17 cells near macrophages within well-formed B-cell follicles to mediate Mtb control. Thus, our data identify new immune characteristics that can be harnessed to improve Th17 recall responses for enhancing vaccine design against TB.

Interleukin 27R regulates CD4+ T cell phenotype and impacts protective immunity during Mycobacterium tuberculosis infection

Loss of IL-27R on T cells results in increased protection from Mycobacterium tuberculosis. Torrado et al. demonstrate that IL-27R^−/− T cells show improved fitness that is associated with decreased expression of cell death molecules, maintenance of IL-2 production, and preferential accumulation in the lung parenchyma and around infected macrophages.

CD4⁺ T cells mediate protection against Mycobacterium tuberculosis (Mtb); however, the phenotype of protective T cells is undefined, thereby confounding vaccination efforts. IL-27 is highly expressed during human tuberculosis (TB), and absence of IL-27R (Il27ra) specifically on T cells results in increased protection. IL-27R deficiency during chronic Mtb infection does not impact antigen-specific CD4⁺ T cell number but maintains programmed death-1 (PD-1), CD69, and CD127 expression while reducing T-bet and killer cell lectin-like receptor G1 (KLRG1) expression. Furthermore, T-bet haploinsufficiency results in failure to generate KLRG1⁺, antigen-specific CD4⁺ T cells, and in improved protection. T cells in Il27ra^−/− mice accumulate preferentially in the lung parenchyma within close proximity to Mtb, and antigen-specific CD4⁺ T cells lacking IL-27R are intrinsically more fit than intact T cells and maintain IL-2 production. Improved fitness of IL-27R–deficient T cells is not associated with increased proliferation but with decreased expression of cell death–associated markers. Therefore, during Mtb infection, IL-27R acts intrinsically on T cells to limit protection and reduce fitness, whereas the IL-27R–deficient environment alters the phenotype and location of T cells. The significant expression of IL-27 in TB and the negative influence of IL-27R on T cell function demonstrate the pathway by which this cytokine/receptor pair is detrimental in TB.

Correlates of Vaccine-Induced Protection against Mycobacterium tuberculosis Revealed in Comparative Analyses of Lymphocyte Populations

A critical hindrance to the development of a novel vaccine against Mycobacterium tuberculosis is a lack of understanding of protective correlates of immunity and of host factors involved in a successful adaptive immune response. Studies from our group and others have used a mouse-based in vitro model system to assess correlates of protection. Here, using this coculture system and a panel of whole-cell vaccines with varied efficacy, we developed a comprehensive approach to understand correlates of protection. We compared the gene and protein expression profiles of vaccine-generated immune peripheral blood lymphocytes (PBLs) to the profiles found in immune splenocytes. PBLs not only represent a clinically relevant cell population, but comparing the expression in these populations gave insight into compartmentally specific mechanisms of protection. Additionally, we performed a direct comparison of host responses induced when immune cells were cocultured with either the vaccine strain Mycobacterium bovis BCG or virulent M. tuberculosis. These comparisons revealed host-specific and bacterium-specific factors involved in protection against virulent M. tuberculosis. Most significantly, we identified a set of 13 core molecules induced in the most protective vaccines under all of the conditions tested. Further validation of this panel of mediators as a predictor of vaccine efficacy will facilitate vaccine development, and determining how each promotes adaptive immunity will advance our understanding of antimycobacterial immune responses.

DosS Is required for the complete virulence of mycobacterium tuberculosis in mice with classical granulomatous lesions

Mycobacterium tuberculosis (Mtb) must counter hypoxia within granulomas to persist. DosR, in concert with sensor kinases DosS and DosT, regulates the response to hypoxia. Yet Mtb lacking functional DosR colonize the lungs of C57Bl/6 mice, presumably owing to the lack of organized lesions with sufficient hypoxia in that model. We compared the phenotype of the Δ-dosR, Δ-dosS, and Δ-dosT mutants to Mtb using C3HeB/FeJ mice, an alternate mouse model where lesions develop hypoxia. C3HeB/FeJ mice were infected via aerosol. The progression of infection was analyzed by tissue bacterial burden and histopathology. A measure of the comparative global immune responses was also analyzed. Although Δ-dosR and Δ-dosT grew comparably to wild-type Mtb, Δ-dosS exhibited a significant defect in bacterial burden and pathology in vivo, accompanied by ablated proinflammatory response. Δ-dosS retained the ability to induce DosR. The Δ-dosS mutant was also attenuated in murine macrophages ex vivo, with evidence of reduced expression of the proinflammatory signature. Our results show that DosS, but not DosR and DosT, is required by Mtb to survive in C3HeB/FeJ mice. The attenuation of Δ-dosS is not due to its inability to induce the DosR regulon, nor is it a result of the accumulation of hypoxia. That the in vivo growth restriction of Δ-dosS could be mimicked ex vivo suggested sensitivity to macrophage oxidative burst. Anoxic caseous centers within tuberculosis lesions eventually progress to cavities. Our results provide greater insight into the molecular mechanisms of Mtb persistence within host lungs.