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Molecular and histopathological characterisation of peripheral nerve and immune cell distributions in normal and virus infected mouse tissues

Al-Shalan, Huda (2022) Molecular and histopathological characterisation of peripheral nerve and immune cell distributions in normal and virus infected mouse tissues. PhD thesis, Murdoch University.

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Both nervous and immune systems can exist as two separated systems in terms of function. However, they are considered the main sensory interfaces that have developed to sense the internal and external environmental stimuli to maintain the host homeostasis and survival in healthy and disease states either. Various branches of the peripheral nervous system (PNS), including the sympathetic and parasympathetic together with the sensory nervous system and the enteric nervous system, interact with the immune system to sustain homeostasis and regulate the immune response of secondary lymphoid tissues and organs (SLTO). The neuro-immune molecular communications are mediated by soluble molecules which have pro-inflammatory or anti-inflammatory impacts, namely, cytokines and chemokines released by the immune system, as well as neurotrophins and neuropeptides released by the PNS. Therefore, the study of neuroimmune interactions is crucial to get more knowledge and to understand the cross-regulation between these vital systems within secondary lymphoid tissues and organs (SLTO), and from another aspect is to investigate the influences of respiratory viral infections on the bidirectional cross-talk. Started with, the specificity of mouse anti-neurofilament heavy (NF-H) ( neuronal antibody) and anti-immune cell antibodies which have been applied in this study through the use of immunofluorescent staining (IF) combined with confocal microscopy to demonstrate such innervation of Peyer's patches, thymus, and spleen, further, a type of the reciprocal relationship of these nerve cells with immune cells within these tissues in normal condition was characterized.

As it is Known, the influenza A virus (IAV) is one of the major pathogens of human and animal respiratory tract infections with epidemics causing significant morbidity and mortality worldwide. To evaluate neuro-immune interactions during the viral infection, the murine model was used and only female mice were utilized in this study since that females are more susceptible than males to being infected by IAVs. Moreover, females can produce neutralizing antibodies, cytokines, and chemokines at higher levels than males during IAV infections (Geurs et al., 2012). Further, influenza A/PR/8/34 H1N1 virus (PR8), is a mouse-adapted influenza strain that provokes the destruction of alveolar type II (ATII) cells in mouse alveoli making it a suitable model. Such experiments showed that the molecular mechanism of the reciprocal neuro-immune relationship was influenced by the infection through the emergence of the immune response against the virus, which was characterized by the presence of immune cells and antigen-presenting cells (APCs) in abundance in situ compared with the control tissues.

This project additionally investigated the metabolic signature and gene-expressed changes that occur in the murine host response to lung inflammation generated by influenza A virus infection. Importantly, metabolites are found inside organisms as either amino acids or tryptophan. Amino acids act as a progenitor to various biomolecules and have a major effect on immune and neuronal functions. Induction of changes in plasma amino acid levels is associated with diseases (Kelly & Pearce, 2021). Tryptophan on the other hand is involved in biological pathways such as the control of inflammation, regulation of energy homeostasis, and synthesis of neurotransmitters. A metabolomic study of blood plasma metabolites has been conducted throughout the experimental infection. The best results obtained were at the acute stage (7 dpi) of the infection revealed a significant difference of six amino acids and one tryptophan pathway metabolites between control and infected samples amongst other time points of the disease. Three metabolites were elevated in plasma at peak infection (taurine, 5-Oxoproline, glutamine) and 4 were lower in infection (serine, glycine, citrulline, indole-3-acetic acid). This is indicative of a neuroprotective, antioxidant, and immunostimulatory phenotype.

To identify gene expression patterns in lung, thymus, spleen, and Peyer’s patches, glial fibrillary acidic protein (GFAP), brain-derived neuropeptide factor (BDNF), and haemagglutinin antigen (HA) of IAV genes were chosen. Analytic data revealed that these genes of interest were expressed by lung cells obviously and showed significant changes between infected and control animals in a comparison with other tissues. On the other hand, at a peak of infection, and when we utilized more neural genes on the same tissues as well as the brain, we noticed that there was a significant difference in both the lung and brain.

To investigate differentially expressed genes, RNA-seq analysis was performed utilizing the data of the recovery stage (21 dpi) of infection comparing control and infected samples, which may have been new insights into the molecular pathogenesis of IAV infection and its impact on the reciprocal neuro-immune interaction. The bioinformatic analysis detected upregulation of a majority of Immunoglobulin genes, immune infiltration, nerve cells, and genes encoding components of various signaling pathways.

In conclusion, more characterization and greater understanding of the neuroimmune interaction by which the PNS might affect the SLTO and its responses, and vice versa in health and disease is further required. Consequently, this can control the pathogenesis of many neuro/immunological as well as infectious diseases by the development of novel and beneficial therapies for the treatment of these diseases.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Medical, Molecular and Forensic Sciences
Supervisor(s): Greene, Wayne, Nicholls, Philip, Ma, Bin and Stumbles, Phil
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