Complement and humoral adaptive immunity in the human choroid plexus: roles for stromal concretions, basement membranes, and epithelium

The choroid plexus (CP) provides a barrier to entry of toxic molecules from the blood into the brain and transports vital molecules into the cerebrospinal fluid. While a great deal is known about CP physiology, relatively little is known about its immunology. Here, we show immunohistochemical data that help define the role of the CP in innate and adaptive humoral immunity. The results show that complement, in the form of C1q, C3d, C9, or C9neo, is preferentially deposited in stromal concretions. In contrast, immunoglobulin (Ig) G (IgG) and IgA are more often found in CP epithelial cells, and IgM is found in either locale. C4d, IgD, and IgE are rarely, if ever, seen in the CP. In multiple sclerosis CP, basement membrane C9 or stromal IgA patterns were common but were not specific for the disease. These findings indicate that the CP may orchestrate the clearance of complement, particularly by deposition in its concretions, IgA and IgG preferentially via its epithelium, and IgM by either mechanism

The quest for a myelin specific magnetic resonance marker of multiple sclerosis pathology : myelin water imaging

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system that is characterized by edema, inflammation, demyelination and axonal loss. However, the mechanisms underlying the clinical evolution and ultimate progression of MS and their relationship to these pathological features are still poorly understood. Magnetic resonance imaging (MRI) has been an invaluable tool for the visualization of MS abnormalities in brain. In this thesis, patients with multiple sclerosis were compared to healthy controls using two non-conventional MR techniques believed to be related to myelin content. First, a model for the evolution of magnetization transfer (MT) abnormalities in patients with MS was proposed based on data collected from a relatively small sample size. The MT ratio (MTR) of normal appearing white matter (NAWM) in brain is normal at clinical onset and then slowly decreases over time, correlating strongly with disease duration. This suggests that the gradual progression in disease seen in patients with MS may be due not only to new lesion formation, but also due to global changes in NAWM. In the immediate months before lesion appearance on conventional MRI there is an abrupt decrease in MTR. Lesion recovery is variable, with some lesions showing good recovery of MTR and others showing no recovery or worsening. The early behaviour of lesions may be predictive of future recovery. Chronic stable lesions have a constant and low MTR. In a larger cross-sectional study, MS normal appearing white matter in brain was found to have a higher water content and lower myelin water fraction than controls. Lesions have increased water content, and a heterogeneous reduction in myelin water fraction. The cause of the water content increase in lesions could be due to either edema or inflammation. As our understanding of T₂ improves, we may be able to distinguish between these two pathologies from the shape of the T₂ distribution. A simple model suggests that the observed 2.2% increase in water content and 16% decrease in myelin water fraction in MS NAWM are the result of diffuse myelin loss. Next, MT and myelin water imaging were compared in lesions and white matter for both an MS patient group, as well as a control group. The myelin water fraction of some white matter structures were found to correlate with MTR, while in others they did not. This regional dependence of the correlation between MTR and myelin water fraction is unexpected and has not been observed elsewhere. Myelin water imaging and MT imaging do however indeed probe different properties of brain tissue: myelin water imaging specifically measures the amount of water trapped between the myelin bilayer based on a given T₂ relaxation time range (typically 0-50ms), while MT probes the interaction between all of the semisolid protons with all of the aqueous protons. The previously observed dissociation between MTR and myelin water fraction is reasonable as while myelin water imaging is a specific marker for myelin content, MT is influenced by many factors which are unrelated to myelin content including exchange rates between the semi-solid and aqueous proton pools, pH and distribution of galactocerebrosides. A change in the size of either the semi-solid or aqueous pool would also effect the measured MT ratio, for example: accumulation of cells such as astrocytes and macrophages which would serve to increase the size of the semi-solid pool, thereby increasing MTR without any increase in myelin content. Likewise, an increase in the aqueous proton pool due to oedema would decrease MTR without any reduction in myelin content. Finally, pathological correlations with myelin water imaging in MS were investigated to validate this technique as an in-vivo measure of myelin content. Twenty-five brain samples were examined and a very strong correlation was found between myelin water imaging and myelin staining as measured by luxol fast blue optical density. The close relationship between myelin and axons is reflected in the strong correlation between the luxol fast blue and Bielschowsky stains which also explains the good correlation between myelin water fraction and the Bielschowsky optical density. This study supports the use of myelin water imaging to study myelin pathology and the role of demyelination and remyelination in MS.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Optimization of a 48 echo magnetic resonance imaging sequence using variable TR data acquisition

Magnetic resonance imaging (MRI) is a very valuable tool for studying the brain. Currently, MRI is the only non-invasive method for investigating myelin. A unique MRI pulse sequence which is used to investigate myelin is a 48 echo CPMG experiment with TR = 3800ms and TE 10 and 50ms. Unfortunately, this experiment takes over 33 minutes to complete, making clinically less feasible to use. By collecting higher order regions of k-space at shorter TR times, the experiment can be shortened, but at a cost of increasing image blurrines and at a potential loss of data. The purpose of this thesis was to investigate collecting different regions of k-space at different TR times in order to try and optimize a new 48 echo variable TR pulse sequence. Simulations were first performed using five spin-echo images with different TR. By creating simulated variable TR images, we were able to qualitatively investigate the resulting blurriness of the images. Visual assesment of the created images and the difference images allowed us to determine what degree of resolution deterioration would still allow us to differentiate between important structures. It was decided that the simulation for 60 out of 128 lines collected at a shorter TR had the optimal decrease in scan time, without too great a compromise in image quality. The variable TR CPMG experiment was then run on 9 phantoms with different T1 and T2 relaxation times. By studying samples with known T1 and T2 relaxation times, we were able to investigate the reliability of the variable TR pulse sequence. Comparing decay curves showed no difference between 0 and 100 lines of k-space collected at a shorter TR - it was only when all 128 lines of kspace were collected at the shorter TR that a decrease in amplitude of the decay curve occurred. Experiments showed that proton density, GMT2 and chi squared of the T2 decay curve fit for the phantoms were unaffected up to and including 100 lines of k-space collected at TR of 2120ms. Finally, in-vivo studies were performed on five volunteers. Comparing the difference in decay curves, proton density and geometric mean T2 showed only very minor differences between data collected using the constant TR sequence and data collected using the variable TR program in which 60 out of 128 k-space lines were collected at a shorter TR of 2120ms. Experiments showed small differences in myelin water fraction, which could be explained by ROI's being drawn slightly different on the constant and variable images. The chi squared was less for the variable TR, which could be caused by smoothing introduced when collecting different k-space lines at different TR's.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Temperature dependence and histological correlation of inhomogeneous magnetization transfer and myelin water imaging in ex vivo brain

Purpose: The promise of inhomogeneous magnetization transfer (ihMT) as a new myelin imaging method was studied in ex vivo human brain tissue and in relation to myelin water fraction (MWF). The temperature dependence of both methods was characterized, as well as their correspondence with a histological measure of myelin content. Unfiltered and filtered ihMT protocols were studied by adjusting the saturation scheme to preserve or attenuate signal from tissue with short dipolar relaxation time T1D. Methods: ihMT ratio (ihMTR) and MWF maps were acquired at 7 T from formalin-fixed human brain samples at 22.5 °C, 30 °C and 37 °C. The impact of temperature on unfiltered ihMTR, filtered ihMTR and MWF was investigated and compared to myelin basic protein staining. Results: Unfiltered ihMTR exhibited no temperature dependence, whereas filtered ihMTR increased with increasing temperature. MWF decreased at higher temperature, with an increasing prevalence of areas where the myelin water signal was unreliably determined, likely related to a reduction in T2 peak separability at higher temperatures ex vivo. MWF and ihMTR showed similar per-sample correlation with myelin staining at room temperature. At 37 °C, filtered ihMTR was more strongly correlated with myelin staining and had increased dynamic range compared to unfiltered ihMTR. Conclusions: Given the temperature dependence of filtered ihMT, increased dynamic range, and strong myelin specificity that persists at higher temperatures, we recommend carefully controlled temperatures close to 37 °C for filtered ihMT acquisitions. Unfiltered ihMT may also be useful, due to its independence from temperature, higher amplitude values, and sensitivity to short T1D components. Ex vivo myelin water imaging should be performed at room temperature, to avoid fitting issues found at higher temperatures

Myelin water imaging in relapsing multiple sclerosis treated with ocrelizumab and interferon beta-1a

Background: Myelin water imaging is a magnetic resonance imaging (MRI) technique that quantifies myelin damage and repair in multiple sclerosis (MS) via the myelin water fraction (MWF). Objective: In this substudy of a phase 3 therapeutic trial, OPERA II, MWF was assessed in relapsing MS participants assigned to interferon beta-1a (IFNb-1a) or ocrelizumab (OCR) during a two-year double-blind period (DBP) followed by a two-year open label extension (OLE) with ocrelizumab treatment. Methods: MWF in normal appearing white matter (NAWM), including both whole brain NAWM and 5 white matter structures, and chronic lesions, was assessed in 29 OCR and 26 IFNb-1a treated participants at weeks 0, 24, 48 and 96 (DBP), and weeks 144 and 192 (OLE), and in white matter for 23 healthy control participants at weeks 0, 48 and 96. Results: Linear mixed-effects models of data from baseline to week 96 showed a difference in the change in MWF over time favouring ocrelizumab in all NAWM regions. At week 192, lesion MWF was lower for participants originally randomised to IFNb-1a compared to those originally randomised to OCR. Controls showed no change in MWF over 96 weeks in any region. Conclusion: Ocrelizumab appears to protect against demyelination in MS NAWM and chronic lesions and may allow for a more permissive micro environment for remyelination to occur in focal and diffusely damaged tissue

48 echo T2 myelin imaging of white matter in first-episode schizophrenia: Evidence for aberrant myelination

Myelin water imaging provides a novel strategy to assess myelin integrity and corresponding clinical relationships in psychosis, of particular relevance in frontal white matter regions. In the current study, T2 myelin water imaging was used to assess the myelin water fraction (MWF) signal from frontal areas in a sample of 58 individuals experiencing first-episode psychosis (FEP) and 44 healthy volunteers. No differences in frontal MWF were observed between FEP subjects and healthy volunteers; however, differences in normal patterns of associations between frontal MWF and age, education and IQ were seen. Significant positive relationships between frontal MWF and age, North American Adult Reading Test (NAART) IQ, and years of completed education were observed in healthy volunteers. In contrast, only the relationship between frontal MWF and NAART IQ was significant after Bonferroni correction in the FEP group. Additionally, significant positive relationships between age and MWF in the anterior and posterior internal capsules, the genu, and the splenium were observed in healthy volunteers. In FEP subjects, only the relationship between age and MWF in the splenium was statistically significant. Frontal MWF was not associated with local white matter volume. Altered patterns of association between age, years of education, and MWF in FEP suggest that subtle disturbances in myelination may be present early in the course of psychosis

Assessing structure and function of myelin in cervical spondylotic myelopathy: Evidence of demyelination

Purpose:To assess the extent of demyelination in cervical spondylotic myelopathy (CSM) using myelin water imaging (MWI) and electrophysiologic techniques.Methods:Somatosensory evoked potentials (SSEPs) and MWI were acquired in 14 patients with CSM and 18 age-matched healthy controls. MWI was performed on a 3.0T whole body magnetic resonance scanner. Myelin water fraction (MWF) was extracted for the dorsal columns and whole cord. SSEPs and MWF were also compared with conventional MRI outcomes, including T2 signal intensity, compression ratio, maximum spinal cord compression (MSCC), and maximum canal compromise (MCC).Results:Group analysis showed marked differences in T2 signal intensity, compression ratio, MSCC, and MCC between healthy controls and patients with CSM. There were no group differences in MWF and SSEP latencies. However, patients with CSM with pathologic SSEPs exhibited reduction in MWF (p &lt; 0.05). MWF was also correlated with SSEP latencies.Conclusion:Our findings provide evidence of decreased myelin content in the spinal cord associated with impaired spinal cord conduction in patients with CSM. While conventional MRI are of great value to define the extent of cord compression, they show a limited correlation with functional deficits (i.e., delayed SSEPs). MWI provides independent and complementary readouts to spinal cord compression, with a high specificity to detect impaired conduction.</jats:sec