Describing the immune cell profile of ventricular cerebrospinal fluid (CSF) in paediatric central nervous system (CNS) infections

Morris, Kate

Describing the immune cell profile of ventricular cerebrospinal fluid (CSF) in paediatric central nervous system (CNS) infections

Thesis / Dissertation

2025

Publisher

University of Cape Town

Department

Division of General Surgery

Faculty

Faculty of Health Sciences

Abstract

Introduction: Paediatric central nervous system (CNS) infections are associated with high mortality rates and neurological disability in survivors due to brain injury caused by cerebral inflammation. Because the brain is difficult to study, the unique characteristics of the neuroinflammatory response are poorly understood. A better understanding of the immune response to these infections could lead to improved host-directed therapies. An important method to study this is the analysis of infected ventricular cerebrospinal fluid (CSF), but there is often a paucity of cells in CSF samples, especially in conditions like tuberculous meningitis (TBM), and these undergo rapid immune cell death after sampling. Consequently, the cell populations in CSF are not well described. Cryopreservation of CSF and flow cytometric analysis have improved the ability to study immune cells in CSF; therefore, these techniques were employed in this study. Aims: This project aimed to 1) describe the cellular immunophenotype and inflammatory mediators in CSF samples from patients with common CNS infections through flow cytometric and Luminex® analysis respectively, and 2) explore changes in immune cells and analytes over time. Methods: CSF samples were prospectively collected during clinically indicated procedures, the cell pellets and supernatant were cryopreserved. Flow cytometric analysis was performed after two weeks of storage at -80°C. Different populations of major peripheral immune cells (CD45+: lymphocytes, monocytes and granulocytes) and CNS-derived immune cells (microglia (CD45-TMEM119+) and astrocytes (CD45-ACSA+) were examined along with their respective sub-groups. The sample supernatants were batch analysed for inflammatory biomarkers including interleukin (IL)-1, IL-6, IL-8, IL-10, IL-1 receptor antagonist (IL-1Ra), tumour necrosis factor (TNF)-, interferon (IFN)-, IFN-, vascular endothelial growth factor (VEGF), monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory proteins (MIP)-1 and interferon-inducible protein 10 (IP-10) using Luminex® technology. Cell proportions and concentrations (using Flow-Count Fluorospheres) and cytokine concentrations were described in admission and serial samples. Results: This study recruited 30 children with CNS infections (including tuberculous and other bacterial meningitis, shunt infections, and ventriculitis) in whom 61 samples were collected (30 admission, 31 serial samples). Microglia (CD45-TMEM119+) were the most abundant cell population on admission and over time. Lymphocytes (CD45+CD3+ and CD45+CD3-) were the most abundant peripheral immune cell, population above granulocytes (CD45+) and monocytes (CD45+CD14+). Cytokines with the highest concentration included IL-1Ra, MCP-1 and IP-10. MCP-1 remained elevated over time whereas overall cytokine concentrations were highest on admission and decreased over time. Cytokine and cell data were influenced by the aetiology of the CNS infection (70% of the cohort comprised patients with TBM). Conclusions: Brain-resident immune cells are important contributors to the neuroinflammatory response to CNS infection, particularly microglia, which are the most abundant immune cell present in the ventricular CSF of these patients. The techniques used in the study could be used at scale to characterise the unique characteristics of the neuroinflammatory response in different CNS infections and inflammatory conditions, which could lead to the development of novel immunomodulatory therapies. The role of microglia in inflammation as well as neurodevelopment is important to consider when studying children.

Keywords

Medicine

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