Neurons as potential immune modulators during central nervous system tuberculosis

Walters, Avril

Neurons as potential immune modulators during central nervous system tuberculosis

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Pathology

Faculty

Faculty of Health Sciences

Abstract

Background Mycobacterium tuberculosis (M. tuberculosis) is the causative pathogen in the pulmonary disease tuberculosis, with both innate and adaptive immunity providing host defence mechanisms against M. tuberculosis infection for positive disease outcomes. There is clinical evidence that individuals with compromised immunity, such as patients with HIV, are at higher risk of bacteria dissemination to the brain and developing central nervous system tuberculosis (CNS-TB), which is often associated with high mortality and morbidity. Neurons have been identified as host cells for M. tuberculosis and display potential immune regulatory capability during infection. It is therefore important to understand how neurons and immune cells, whether resident or peripheral shape functional and protective immune responses against CNS-TB infection. Objective Neurons have demonstrated potential to participate in a tightly regulated neuroimmune networks. This study aims to investigate the immune modulatory abilities of neurons in CNS-TB. Furthermore, it aims to highlight the importance of functional systemic immune responses as an integral aspect of CNS protective immunity. Methods This study incorporated both a culture based in vitro approach as well as in vivo investigation using a mouse model of infection. Initial studies focused on primary murine hippocampal neurons which were infected with M. tuberculosis H37Rv; RNA was extracted for microarray analysis and the culture supernatants were processed for Luminex Multiplex analysis to assess neuronal secretion of 11 immunologically active analytes. To identify the immune regulatory abilities of neurons, the supernatants from infected neurons were transferred to freshly isolated leukocytes from mouse blood and used as conditioned medium for an overnight stimulation. The leukocytes were then analysed by flow cytometry. In vivo experiments were performed on C57BL/6, NSG and BLT-NSG humanised mice. Mice were infected with M. tuberculosis H37Rv by intracerebral inoculation. Mice were monitored for body condition, weight loss and signs of neurodegeneration over the period of infection. Infected brains were harvested, and single cell suspensions were generated for flow cytometry analysis. Results M. tuberculosis infected primary hippocampal neurons showed transcriptional differences when compared to non-infected neurons. Genes expressed in infected neurons clustered separately from non-infected neurons representing distinct transcriptomic profiles. The transcriptomic results were validated by protein analysis, which showed significant upregulated protein expression in primary neuron cultures after M. tuberculosis infection. To identify the immune modulatory abilities, stimulation of leukocytes with neuronal conditioned media resulted in significant cell activation where CD45+ leukocytes expressing MHC class II and IL1β. In vivo challenge studies showed that immune competent C57BL/6 mice remained healthy across the period of infection, however immune incompetent NSG and humanised BLT-NSG mice presented with deteriorating health. Furthermore, although the BLTNSG mice were reconstituted with human immune cells and showed functional human leukocyte recruitment to the brain, mice were unable to control the infection. Conclusion The findings from this study show that neurons are active cell participants during CNS infections capable of generating immune responses and perform immune modulatory functions in response to M. tuberculosis infection. Moreover, it is imperative to have a functional systemic immune system characterised by functionally effective leukocyte recruitment to induce adequate protection as part of a comprehensive protective host immune response against CNS-TB.

Keywords

tuberculosis

immune modulators

Reference:

Collections

PhD / Doctoral

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