Deciphering the role of innate and adaptive immunity following traumatic spinal cord injury: a route to improved outcomes

Biggins, Patrick (2016). Deciphering the role of innate and adaptive immunity following traumatic spinal cord injury: a route to improved outcomes PhD Thesis, School of Biomedical Sciences, The University of Queensland. doi:10.14264/uql.2017.45

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Author Biggins, Patrick
Thesis Title Deciphering the role of innate and adaptive immunity following traumatic spinal cord injury: a route to improved outcomes
School, Centre or Institute School of Biomedical Sciences
Institution The University of Queensland
DOI 10.14264/uql.2017.45
Publication date 2016-12-21
Thesis type PhD Thesis
Supervisor Marc Ruitenberg
Trent Woodruff
Total pages 215
Language eng
Subjects 1107 Immunology
1109 Neurosciences
Formatted abstract
Traumatic SCI initiates a self-propagating cycle of neuro-inflammation and –degeneration (the ‘secondary injury’). Secondary injury involves activation of local glial cells and initiates a wave of cytokine production and immune cell recruitment. The principal goal of this thesis was to better understand individual segments of the immune response that contribute to secondary injury pathology. With this goal in mind and using a contusive experimental spinal cord injury model, a particular focus was placed on ‘macrophage inducible Ca2+ (C-type) lectin’ (Mincle), a macrophage receptor for death ligands, along with the complement system activation, and also the phosphoinositide 3-kinase signalling pathway.

I report in this thesis that Mincle knockout mice exhibited no significant differences to wild-type (WT) controls with regards to locomotor recovery or histopathological measures. This suggests that Mincle activity does not affect outcomes in a model of moderate-severe traumatic SCI.

I have also investigated a putative role for the novel C5a receptor 2 (C5aR2) following SCI. From this work, it was found that C5aR2-knockout animals (C5ar2-/-) exhibited significantly worsened locomotor recovery, decreased myelin sparing, increased GFAP reactivity and larger lesion volumes (as determined by MRI) following injury when compared with WT controls. Changes in pro-inflammatory cytokine concentrations and immune cell mobilisation were not found to be likely contributors to this phenotype. Pharmacological inhibition of C5aR1 did, however, fully rescue the negative phenotype seen in C5ar2-/- mice, suggesting that C5aR2 acts as a negative regulator of C5a-C5aR1 signalling in this pathology. Cumulatively, the data suggests that deregulated C5aR1 activity is driving the worsened phenotype in the C5aR2-knockout animals and, with an injurious role for C5aR1 previously established, that upregulating C5aR2 may be a therapeutic strategy to improve SCI outcomes.

Finally, a possible role for the delta isoform of the phosphoinositide 3-kinase pathway, PI3Kδ, was investigated in the context of SCI. PI3Kδ genetic knockout (p110δD910A/D910A) mice exhibited significantly improved hindlimb locomotion, increased myelin sparing and decreased GFAP reactivity post-injury when compared with WT mice. Intraparenchymal pro-inflammatory IFN-γ and CXCL1, along with circulating MCP-1, was significantly reduced in knockout animals. Neutrophils recruited to the lesion epicentre at one day post injury (dpi) were significantly smaller in p110δD910A/D910A mice than WT animals, suggesting a decreased activation state. Flow cytometry experiments revealed p110δD910A/D910A mice have significantly increased circulating non-classical M2 monocyte/macrophage populations at 14dpi. A significant reduction in activated, IgG+ B cells and a strong reducing trend for activated T cells was also seen in the circulation of p110δD910A/D910A mice at 14dpi. Activated B cells which secrete CNS-epitope specific autoantibodies are known to contribute to secondary pathology following SCI. Histological analysis at experimental endpoint (35dpi) revealed significantly reduced numbers of activated B cells and decreased IgG reactivity in the lesion epicentre of p110δD910A/D910A animals. Furthermore, preliminary analysis of matched naïve and post-injury serum demonstrated that serum from post-injury p110δD910A/D910A mice is significantly less autoreactive for CNS proteins than that from post-injury WT mice. Cumulatively, these findings suggests that the improvement in locomotion of p110δD910A/D910A mice is driven by a less toxic (through decreased pro-inflammatory cytokine concentrations and chemokine gradients) microenvironment in the sub-1dpi phase. Additionally, reduced B cell activation and decreased autoantibody production likely contributes to the improvements in recovery during the more chronic phase of injury.

Collectively, the novel information revealed in this thesis regarding the specific contribution of components of the immune response to neuro-inflammation following SCI, may assist in the development of optimally targeted therapeutic approaches for treating acute SCI in human patients.
Keyword Spinal cord injury
B cell
T cell

Document type: Thesis
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Created: Wed, 14 Dec 2016, 00:52:41 EST by Patrick Biggins on behalf of Learning and Research Services (UQ Library)