Differential mast cell numbers and characteristics in human tuberculosis pulmonary lesions

Multiomic analysis identifies suppressive myeloid cell populations in human TB granulomas

Tuberculosis (TB) remains a major global health challenge, particularly in the context of multidrug-resistant (MDR) Mycobacterium tuberculosis (Mtb). Host-directed therapies (HDTs) have been proposed as adjunctive therapy to enhance immune control of infection. Recently, one such HDT, pharmacologic modulation of myeloid-derived suppressor cells (MDSCs), has been proposed to treat MDR-TB. While MDSCs have been well characterized in cancer, their role in TB pathogenesis remains unclear. To investigate whether MDSCs or other myeloid suppressor populations contribute to TB granuloma microenvironments (GME), we performed spatial transcriptional profiling and single-cell immunophenotyping on eighty-four granulomas in lung specimens from three individuals with active disease. Granulomas were histologically classified based on H&E staining, and transcriptional signatures were compared across regions of interest (ROIs) at different states of granuloma maturation. Our analysis revealed that immune suppression within granuloma was not primarily driven by classical MDSCs but rather by multiple myeloid cell subsets, including dendritic cells expressing indoleamine 2,3 dioxygenase-1 expressing (IDO1+ DCs). IDO1+ DCs were the most frequently observed suppressive myeloid cells, particularly in cellular regions, and their spatial proximity to activated T cells suggested localized immunosuppression. Importantly, granulomas at different stages contained distinct proportions of suppressor myeloid cells, with necrotic and cellular regions showing different myeloid phenotypes that may influence granuloma progression. Gene set enrichment analysis (GSEA) further indicated that elevated IDO1 expression was associated with a complex immune response that balanced suppressive signaling, immune activation, and cellular metabolism. These findings suggest that classical MDSCs, as defined in tumor microenvironments, likely play a minor role in TB, whereas IDO1+ DCs may be key regulators of immune suppression in granulomas influencing local Mtb control in infected lung. A deeper understanding of the role of IDO1+ suppressive myeloid cells in TB granulomas is essential to assessing their potential as therapeutic targets in TB treatment.

Impaired control of Mycobacterium tuberculosis infection in mast cell-deficient KitW-sh/W-sh mice

Tuberculosis (TB) is a global health problem with diverse clinical manifestations. Different cells of the immune response participate in containing the infection, mainly through the development of granulomas. Mast cells (MCs) are hematopoietic cells that participate in the immune response to different pathogens, and in vitro evidence indicates that they can be activated by Mycobacterium tuberculosis (Mtb). The aim of this study was to evaluate the role of MCs in a murine TB model. We observed that KitW-sh/W-sh mast cell-deficient mice showed increased bacterial load in the lungs and the spleen compared to wild-type C57BL/6 mice. Furthermore, MC-deficient mice showed fewer pulmonary granulomas but an early higher inflammatory infiltrate. Interestingly, serum cytokine levels were altered in MC-deficient mice, which showed increased levels of IL-4, IL-5, and IL-22 during the early phase of the infection but increased levels of IFN-γ, IL-9, IL-10, and IL-21 during the late phase of the infection. These results show that mast cells play an important role during Mtb infection by modulating the immune response to the bacteria.

Mast cells promote pathology and susceptibility in tuberculosis

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (Mtb), infects approximately one-fourth of the world's population. While most infected individuals are asymptomatic, latent TB infection (LTBI) can progress to cause pulmonary TB (PTB). We recently reported an increased accumulation of mast cells (MCs) in lungs of macaques with PTB, compared with LTBI in macaques. MCs respond in vitro to Mtb exposure via degranulation and by inducing proinflammatory cytokines. In the current study, we show the dominant production of chymase by MCs in granulomas of humans and macaques with PTB. Using scRNA seq analysis, we show that MCs found in LTBI and healthy lungs in macaques are enriched in genes involved in tumor necrosis factor alpha, cholesterol and transforming growth factor beta signaling. In contrast, MCs clusters found in PTB express transcriptional signatures associated with interferon gamma, oxidative phosphorylation, and MYC signaling. Additionally, MC deficiency in the mouse model showed improved control of Mtb infection that coincided with reduced accumulation of lung myeloid cells and diminished inflammation at chronic stages. Thus, these collective results provide novel evidence for the pathological contribution of MCs during Mtb infection and may represent a novel target for host directive therapy for TB.

Immune responses induced by Mycobacterium tuberculosis heat-resistant antigen (Mtb-HAg) upon co-administration with Bacillus Calmette-Guérin in mice

OBJECTIVES

To preliminarily assess the immunogenicity of Mtb-HAg in mice and the synergistic effect provided by HAg when co-immunised with BCG.

METHODS

Mice were randomly grouped for different immunisations and then spleens were aseptically removed and lymphocytes were extracted for immediate detection of cytokines transcript levels and stimulation index(SI), cytokine secretion and multifunctional antigen-specific T cells were detected after incubation for different times.

RESULTS

HAg extracted from active Mtb is a group of mixed polypeptides with molecular weights of (10-14) kDa. It can significantly stimulate lymphocytes proliferation and increase SI. Injection of HAg alone and in combination with BCG induced significantly higher numbers of multifunctional antigen-specific T cells including CD4+ IFN-γ+, CD4+ IL-2+, CD8+ IFN-γ+, and CD8+ IL-2+ cells than that in BCG-treated mice. Co-immunisation induced the secretion of higher levels of IFN-γ, TNF-α, IL-2 and IL-4 and increased their mRNA expression levels. Significant increases in the transcription levels of IL-10, IL-12 and IL-17 were observed in the co-immunised group with the assistance of HAg.

CONCLUSION

We demonstrated that HAg has favourable immunogenicity, triggers a stronger Th1-type immune response and proposed the hypothesis that HAg can be used as a BCG booster to further enhance the benefits of BCG.

A novel Mycobacterium Tuberculosis antigen, MTB48 enhances inflammatory response in LPS-induced RAW264.7 macrophage immune cells

Mtb (Mycobacterium tuberculosis) is a pathogenic bacterium that causes tuberculosis infection (TB). Mtb-secreted proteins have recently been investigated as virulence factors, as well as therapeutic and vaccine possibilities. The early-secreted antigen target MTB48 is one of these proteins that has been explored as a cocktail antigen in the serodiagnosis of active tuberculosis. However, there exists no information about the function or control of MTB48's inflammatory activity in macrophages at the site of inflammation. As a result, the goal of this research was to figure out what processes are involved in MTB48's function. MTB48 stimulated inflammation in LPS induced macrophages at both the protein and mRNA levels, which was interesting. MTB48 aided LPS induced IB phosphorylation and NF-κB translocation. MTB48 also led to the phosphorylation of MAPK signaling protein. These findings imply that MTB48 can enhance inflammatory activity via NF-κB and MAPK signaling by upregulating COX-2, iNOS, NO and PGE2. Many tuberculosis antigens have been tested for the development of rapid serological diagnosis. The results of this study suggest that MTB48 is a very high conservative antigen and is a major factor causing inflammatory reactions, suggesting that it can help control and diagnose tuberculosis.

Early innate cell interactions with Mycobacterium tuberculosis in protection and pathology of tuberculosis

Tuberculosis (TB) remains a significant global health challenge, claiming the lives of up to 1.5 million individuals annually. TB is caused by the human pathogen Mycobacterium tuberculosis (Mtb), which primarily infects innate immune cells in the lungs. These immune cells play a critical role in the host defense against Mtb infection, influencing the inflammatory environment in the lungs, and facilitating the development of adaptive immunity. However, Mtb exploits and manipulates innate immune cells, using them as favorable niche for replication. Unfortunately, our understanding of the early interactions between Mtb and innate effector cells remains limited. This review underscores the interactions between Mtb and various innate immune cells, such as macrophages, dendritic cells, granulocytes, NK cells, innate lymphocytes-iNKT and ILCs. In addition, the contribution of alveolar epithelial cell and endothelial cells that constitutes the mucosal barrier in TB immunity will be discussed. Gaining insights into the early cellular basis of immune reactions to Mtb infection is crucial for our understanding of Mtb resistance and disease tolerance mechanisms. We argue that a better understanding of the early host-pathogen interactions could inform on future vaccination approaches and devise intervention strategies.

Granulocytes subsets and their divergent functions in host resistance to Mycobacterium tuberculosis - a 'tipping-point' model of disease exacerbation

Granulocytes are innate immune effector cells with essential functions in host resistance to bacterial infections. I will discuss emerging evidence that during Mycobacterium tuberculosis infection, counter-intuitively, eosinophils are host-protective while neutrophils are host detrimental. Additionally, I will propose a 'tipping-point' model in which neutrophils are an integral part of a feedforward loop driving tuberculosis disease exacerbation.

Platelets and mast cells promote pathogenic eosinophil recruitment during invasive fungal infection via the 5-HIAA-GPR35 ligand-receptor system

Cryptococcus neoformans is the leading cause of fungal meningitis and is characterized by pathogenic eosinophil accumulation in the context of type-2 inflammation. The chemoattractant receptor GPR35 is expressed by granulocytes and promotes their migration to the inflammatory mediator 5-hydroxyindoleacetic acid (5-HIAA), a serotonin metabolite. Given the inflammatory nature of cryptococcal infection, we examined the role of GPR35 in the circuitry underlying cell recruitment to the lung. GPR35 deficiency dampened eosinophil recruitment and fungal growth, whereas overexpression promoted eosinophil homing to airways and fungal replication. Activated platelets and mast cells were the sources of GPR35 ligand activity and pharmacological inhibition of serotonin conversion to 5-HIAA, or genetic deficiency in 5-HIAA production by platelets and mast cells resulted in more efficient clearance of Cryptococcus. Thus, the 5-HIAA-GPR35 axis is an eosinophil chemoattractant receptor system that modulates the clearance of a lethal fungal pathogen, with implications for the use of serotonin metabolism inhibitors in the treatment of fungal infections.

Pyogranulomatous dermatitis with Enterococcus faecalis in a spotted seal (Phoca larga)

BACKGROUND

Cutaneous infections are important diseases in captive and free-ranging pinnipeds and are associated with various causative agents. Some special agents, such as fungi, morbillivirus and mycobacteria, can cause cutaneous specific granulomatous inflammation.

OBJECTIVES

To identity the cause of chronic dermatitis in a spotted seal in an aquarium.

METHODS

Herein, we analyze the clinical history and cutaneous samples of the spotted seal through differential diagnosis (histopathology, microorganism culture, special histochemical staining methods, PCR), and antibiotic susceptibility test.

RESULTS

This is a rare pyogranulomatous dermatitis case caused by E. faecalis in a captive adult male spotted seal (Phoca largha) in an aquarium.

CONCLUSIONS

We provide a meaningful approach to the diagnosis and treatment of bacterial dermatitis in pinnipeds.

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.

Bacillus Calmette-Guérin-Induced Human Mast Cell Activation Relies on IL-33 Priming

Bacillus Calmette-Guérin (BCG) vaccine is an attenuated strain of Mycobacterium bovis that provides weak protection against tuberculosis (TB). Mast cells (MCs) are tissue-resident immune cells strategically that serve as the first line of defence against pathogenic threats. In this study, we investigated the response of human MCs (hMCs) to BCG. We found that naïve hMCs exposed to BCG did not secrete cytokines, degranulate, or support the uptake and intracellular growth of bacteria. Since we could show that in hMCs IL-33 promotes the transcription of host-pathogen interaction, cell adhesion and activation genes, we used IL-33 for cell priming. The treatment of hMCs with IL-33, but not IFN-γ, before BCG stimulation increased IL-8, MCP-1 and IL-13 secretion, and induced an enhanced expression of the mycobacteria-binding receptor CD48. These effects were comparable to those caused by the recombinant Mycobacterium tuberculosis (Mtb) 19-KDa lipoprotein. Finally, stimulation of hMCs with IL-33 incremented MC-BCG interactions. Thus, we propose that IL-33 may improve the immunogenicity of BCG vaccine by sensitising hMCs.

Uncovering the Mast Cell Response to Mycobacterium tuberculosis

The immunologic mechanisms that contribute to the response to Mycobacterium tuberculosis infection still represent a challenge in the clinical management and scientific understanding of tuberculosis disease. In this scenario, the role of the different cells involved in the host response, either in terms of innate or adaptive immunity, remains key for defeating this disease. Among this coordinated cell response, mast cells remain key for defeating tuberculosis infection and disease. Together with its effector’s molecules, membrane receptors as well as its anatomical locations, mast cells play a crucial role in the establishment and perpetuation of the inflammatory response that leads to the generation of the granuloma during tuberculosis. This review highlights the current evidences that support the notion of mast cells as key link to reinforce the advancements in tuberculosis diagnosis, disease progression, and novel therapeutic strategies. Special focus on mast cells capacity for the modulation of the inflammatory response among patients suffering multidrug resistant tuberculosis or in co-infections such as current COVID-19 pandemic.

Immunosuppressive Mechanisms in Brucellosis in Light of Chronic Bacterial Diseases

Brucellosis is considered one of the major zoonoses worldwide, constituting a critical livestock and human health concern with a huge socio-economic burden. Brucella genus, its etiologic agent, is composed of intracellular bacteria that have evolved a prodigious ability to elude and shape host immunity to establish chronic infection. Brucella's intracellular lifestyle and pathogen-associated molecular patterns, such as its specific lipopolysaccharide (LPS), are key factors for hiding and hampering recognition by the immune system. Here, we will review the current knowledge of evading and immunosuppressive mechanisms elicited by Brucella species to persist stealthily in their hosts, such as those triggered by their LPS and cyclic β-1,2-d-glucan or involved in neutrophil and monocyte avoidance, antigen presentation impairment, the modulation of T cell responses and immunometabolism. Attractive strategies exploited by other successful chronic pathogenic bacteria, including Mycobacteria, Salmonella, and Chlamydia, will be also discussed, with a special emphasis on the mechanisms operating in brucellosis, such as granuloma formation, pyroptosis, and manipulation of type I and III IFNs, B cells, innate lymphoid cells, and host lipids. A better understanding of these stratagems is essential to fighting bacterial chronic infections and designing innovative treatments and vaccines.

In the Thick of It: Formation of the Tuberculous Granuloma and Its Effects on Host and Therapeutic Responses

The defining pathology of tuberculosis is the granuloma, an organized structure derived from host immune cells that surrounds infecting Mycobacterium tuberculosis. As the location of much of the bacteria in the infected host, the granuloma is a central point of interaction between the host and the infecting bacterium. This review describes the signals and cellular reprogramming that drive granuloma formation. Further, as a central point of host-bacterial interactions, the granuloma shapes disease outcome by altering host immune responses and bacterial susceptibility to antibiotic treatment, as discussed herein. This new understanding of granuloma biology and the signaling behind it highlights the potential for host-directed therapies targeting the granuloma to enhance antibiotic access and tuberculosis-specific immune responses.