Interaction between Mycobacterium tuberculosis, Mycobacterium bovis, Mycobacterium avium subspecies paratuberculosis with the enteric glia and microglial cells

Potential of Neuroinflammation-Modulating Strategies in Tuberculous Meningitis: Targeting Microglia

Tuberculous meningitis (TBM) is the most severe complication of tuberculosis (TB) and is associated with high rates of disability and mortality. Mycobacterium tuberculosis (M. tb), the infectious agent of TB, disseminates from the respiratory epithelium, breaks through the blood-brain barrier, and establishes a primary infection in the meninges. Microglia are the core of the immune network in the central nervous system (CNS) and interact with glial cells and neurons to fight against harmful pathogens and maintain homeostasis in the brain through pleiotropic functions. However, M. tb directly infects microglia and resides in them as the primary host for bacillus infections. Largely, microglial activation slows disease progression. The non-productive inflammatory response that initiates the secretion of pro-inflammatory cytokines and chemokines may be neurotoxic and aggravate tissue injuries based on damages caused by M. tb. Host-directed therapy (HDT) is an emerging strategy for modulating host immune responses against diverse diseases. Recent studies have shown that HDT can control neuroinflammation in TBM and act as an adjunct therapy to antibiotic treatment. In this review, we discuss the diverse roles of microglia in TBM and potential host-directed TB therapies that target microglia to treat TBM. We also discuss the limitations of applying each HDT and suggest a course of action for the near future.

Interactions between CNS and immune cells in tuberculous meningitis

The central nervous system (CNS) harbors its own special immune system composed of microglia in the parenchyma, CNS-associated macrophages (CAMs), dendritic cells, monocytes, and the barrier systems within the brain. Recently, advances in the immune cells in the CNS provided new insights to understand the development of tuberculous meningitis (TBM), which is the predominant form of Mycobacterium tuberculosis (M.tb) infection in the CNS and accompanied with high mortality and disability. The development of the CNS requires the protection of immune cells, including macrophages and microglia, during embryogenesis to ensure the accurate development of the CNS and immune response following pathogenic invasion. In this review, we summarize the current understanding on the CNS immune cells during the initiation and development of the TBM. We also explore the interactions of immune cells with the CNS in TBM. In the future, the combination of modern techniques should be applied to explore the role of immune cells of CNS in TBM.

Gliosis, misfolded protein aggregation, and neuronal loss in a guinea pig model of pulmonary tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis infection, is an ongoing epidemic with an estimated ten million active cases of the disease worldwide. Pulmonary tuberculosis is associated with cognitive and memory deficits, and patients with this disease are at an increased risk for Parkinson's disease and dementia. Although epidemiological data correlates neurological effects with peripheral disease, the pathology in the central nervous system is unknown. In an established guinea pig model of low-dose, aerosolized Mycobacterium tuberculosis infection, we see behavior changes and memory loss in infected animals. We correlate these findings with pathological changes within brain regions related to motor, cognition, and sensation across disease progression. This includes microglial and astrocytic proliferation and reactivity. These cellular changes are followed by the aggregation of neurotoxic amyloid β and phosphorylated tau and, ultimately, neuronal degeneration in the hippocampus. Through these data, we have obtained a greater understanding of the neuropathological effects of a peripheral disease that affects millions of persons worldwide.

Neutrophil-Mediated Immunopathology and Matrix Metalloproteinases in Central Nervous System - Tuberculosis

Tuberculosis (TB) remains one of the leading infectious killers in the world, infecting approximately a quarter of the world’s population with the causative organism Mycobacterium tuberculosis (M. tb). Central nervous system tuberculosis (CNS-TB) is the most severe form of TB, with high mortality and residual neurological sequelae even with effective TB treatment. In CNS-TB, recruited neutrophils infiltrate into the brain to carry out its antimicrobial functions of degranulation, phagocytosis and NETosis. However, neutrophils also mediate inflammation, tissue destruction and immunopathology in the CNS. Neutrophils release key mediators including matrix metalloproteinase (MMPs) which degrade brain extracellular matrix (ECM), tumor necrosis factor (TNF)-α which may drive inflammation, reactive oxygen species (ROS) that drive cellular necrosis and neutrophil extracellular traps (NETs), interacting with platelets to form thrombi that may lead to ischemic stroke. Host-directed therapies (HDTs) targeting these key mediators are potentially exciting, but currently remain of unproven effectiveness. This article reviews the key role of neutrophils and neutrophil-derived mediators in driving CNS-TB immunopathology.

Affinity of Mycobacterium tuberculosis strains for M059K microglial cells after migration through A549 alveolar epithelium

Tuberculosis (TB) remains a major threat worldwide while central nervous system TB (CNS-TB) is one of the most severe forms of extrapulmonary TB. CNS-TB develops as a secondary infection during the hematogenous spread of Mycobacterium tuberculosis (M. tuberculosis) from the lungs to the CNS. Factors influencing the dissemination of the bacilli to the CNS have not been studied extensively. This study evaluated the transmigration ability through the alveolar epithelium and adhesion and invasion capacity of glial cells of M. tuberculosis strains of varying drug susceptibility and genotype profiles using an in vitro co-culture model. A549 alveolar epithelial cells and M059K glial cells were co-cultured in a Transwell plate with A549 cells cultured in the upper chamber and M059K glial cells in the lower chamber. A549 epithelial cells were infected with F15/LAM4/KZN (susceptible, MDR, XDR), Beijing (susceptible, XDR), F11 (susceptible), F28 (MDR), and H37Rv strains of M. tuberculosis. The transmigration of an A549 monolayer and subsequent adhesion and invasion rates of M059K cells were established. The susceptible and XDR variants of the F15/LAM4/KZN strain transmigrate the alveolar epithelial cell monolayer more efficiently than the MDR variant. The Beijing-XDR variant showed a high transmigration rate, while the susceptible variant showed no transmigration ability. Similar to the MDR F15/LAM4/KZN, the F28 and F11 strains showed a low dissemination ability. The bacteria were still capable to adhere to M059K glial cells after passage through the A549 cells. We conclude that M. tuberculosis isolates that passed through a monolayer of A549 alveolar epithelium by transcellular migration can still adhere to M059K glial cells. There is no genetic link between resistance and transmigration.

How did Lou Gehrig get Lou Gehrig's disease? Mycobacterium avium subspecies paratuberculosis in manure, soil, dirt, dust and grass and amyotrophic lateral sclerosis (motor neurone disease) clusters in football, rugby and soccer players

There are several suspected infectious causes of amyotrophic lateral sclerosis (ALS) or motor neurone disease including HIV-1 and species of Brucella, Cyanobacteria and Schistosoma. The increased rates and clusters of ALS in amateur and professional outdoor sports players including rugby, football and soccer players suggest a microorganism present in the grass, dirt and dust they play on and in may be a causative factor. The probable zoonosis Mycobacterium avium subspecies paratuberculosis (MAP) is heavily excreted in an infected domestic ruminant's feces or manure and is extensively distributed throughout the soil in countries where MAP infection of domestic livestock is longstanding. Like other zoonotic pathogens, MAP can be transmitted to humans by inhalation of aerosolized pathogen-contaminated soil, by direct contact of pathogen-contaminated grass, dirt and dust with mucus membranes lining the nose or mouth or through abrasions and cuts in the skin. Outdoor sports players may develop ALS after multiple oral, nasal or subcutaneous doses of MAP present in the dirt, dust and grass of their playing fields.

Glial fibrillary acidic protein-immunoreactive enteroglial cells in the jejunum of cattle

Enteroglial cells (EGCs) play critical roles in human health and disease, however, EGC-dependent neuropathies also affect commercially important animal species. Due to the lack of data on the distribution and phenotypic characterization of the EGCs throughout the bovine gastrointestinal tract, in this study the topographic localization of EGCs in the jejunum of healthy cattle was investigated by immunofluorescence using the glial specific marker glial fibrillary acidic protein (GFAP) and the panneuronal marker PGP 9.5. This analysis was conducted on both cryosections and whole mount preparations including the myenteric and the submucous plexuses of the bovine jejunum. The results obtained showed the presence of a large subpopulation of GFAP-expressing EGCs in the main plexuses and within the muscle layers, whereas only few GFAP-positive glial processes were found within the deeper layer of the mucosa, and they never reached the mucosal epithelium. Three different EGC subtypes, namely I, III and IV types were recognized in the examined tract of the bovine intestine. Overall, our results provide the basis for future investigations aimed at elucidating the functional role of the GFAP-containing EGCs which is crucial for a better understanding of the physio-pathology of the bovine intestine.

Microglia are crucial regulators of neuro-immunity during central nervous system tuberculosis

Mycobacterium tuberculosis (M. tuberculosis) infection of the central nervous system (CNS) is the most devastating manifestation of tuberculosis (TB), with both high mortality and morbidity. Although research has been fueled by the potential therapeutic target microglia offer against neurodegenerative inflammation, their part in TB infection of the CNS has not been fully evaluated nor elucidated. Yet, as both the preferential targets of M. tuberculosis and the immune-effector cells of the CNS, microglia are likely to be key determinants of disease severity and clinical outcomes. Following pathogen recognition, bacilli are internalized and capable of replicating within microglia. Cellular activation ensues, utilizing signaling molecules that may be neurotoxic. Central to initiating, orchestrating and modulating the tuberculous immune response is microglial secretion of cytokines and chemokines. However, the neurological environment is unique in that inflammatory signals, which appear to be damaging in the periphery, could be beneficial by governing neuronal survival, regeneration and differentiation. Furthermore, microglia are important in the recruitment of peripheral immune cells and central to defining the pro-inflammatory milieu of which neurotoxicity may result from many of the participating local or recruited cell types. Microglia are capable of both presenting antigen to infiltrating CD4(+) T-lymphocytes and inducing their differentiation-a possible correlate of protection against M. tuberculosis infection. Clarifying the nature of the immune effector molecules secreted by microglia, and the means by which other CNS-specific cell types govern microglial activation or modulate their responses is critical if improved diagnostic and therapeutic strategies are to be attained. Therefore, this review evaluates the diverse roles microglia play in the neuro-immunity to M. tuberculosis infection of the CNS.