Complement activation and increased anaphylatoxin receptor expression are associated with cortical grey matter lesions and the compartmentalised inflammatory response of multiple sclerosis

Abstract

BackgroundThe extent of cortical pathology is an important determinant of multiple sclerosis (MS) severity. Cortical demyelination and neurodegeneration are related to inflammation of the overlying leptomeninges, a more inflammatory CSF milieu and with parenchymal microglia and astroglia activation. These are all components of the compartmentalised inflammatory response. Compartmentalised inflammation is a feature of progressive MS, which is not targeted by disease modifying therapies. Complement is differentially expressed in the MS CSF and complement, and complement receptors, are associated with demyelination and neurodegeneration.MethodsTo better understand if complement activation in the leptomeninges is associated with underlying cortical demyelination, inflammation, and microglial activation, we performed a neuropathological study of progressive MS (n = 22, 14 females), neuroinflammatory (n = 8), and non-neurological disease controls (n = 10). We then quantified the relative extent of demyelination, connective tissue inflammation, complement, and complement receptor positive microglia/macrophages.ResultsComplement was elevated at the leptomeninges, subpial, and within and around vessels of the cortical grey matter. The extent of complement C1q immunoreactivity correlated with connective tissue infiltrates, whilst activation products C4d, Bb, and C3b associated with grey matter demyelination, and C3a receptor 1+ and C5a receptor 1+ microglia/macrophages closely apposed C3b labelled cells. The density of C3a receptor 1+ and C5a receptor 1+ cells was increased at the expanding edge of subpial and leukocortical lesions. C5a receptor 1+ cells expressed TNFα, iNOS and contained puncta immunoreactive for proteolipid protein, neurofilament and synaptophysin, suggesting their involvement in grey matter lesion expansion.InterpretationThe presence of products of complement activation at the brain surfaces, their association with the extent of underlying pathology and increased complement anaphylatoxin receptor positive microglia/macrophages at expanding cortical grey matter lesions, could represent a target to modify compartmentalised inflammation and cortical demyelination.

Digital Pathology Identifies Associations between Tissue Inflammatory Biomarkers and Multiple Sclerosis Outcomes

“…The rating reflected the most significant cellular infiltrate in the intact leptomeninges and/or perivascular space noted for that case. The extent of leptomeningeal and perivascular infiltration was scored semi-quantitatively as absent = 0; mild (1+, equivalent to 5–30 cells); moderate (2+, equivalent to 30–50 cells); and substantial (3+, equivalent to 50+ cells in a dense infiltrate) in accordance with previous descriptions [ 3 , 25 ]. There were insufficient numbers of cut sections to perform the immunostaining required to confirm if any of the 3+ rated leptomeningeal aggregates represented bona-fide B-cell follicle-like structures.…”

“…The immunohistochemical staining protocol methods used are as reported in [ 23 , 25 ]. The antigen retrieval step with 0.05% citraconic anhydride ( v / v ) was conducted on FFPE tissue.…”

Comparing the Pathology, Clinical, and Demographic Characteristics of Younger and Older‐Onset Multiple Sclerosis

“…Immunohistochemistry was performed as described 34 by the authors with diaminobenzidine (Impact DAB; Vector Labs, Newmark, CA, USA) as the chromogen. In all instances, the relevant immunoglobulin G control or the absence of the secondary detection antibody yielded no signal.…”

“…Chronic inactive lesions most often presented as sharply demarcated plaques characterized by the presence of human leukocyte antigen + microglia/ macrophages at the lesion border at densities indistinguishable to the surrounding normal appearing tissue. The presence of one or more actively (active or chronic active) demyelinating lesion in the sampled blocks defined a case as harboring “active lesions.” A combined measure of relative leptomeningeal and perivascular immune cell infiltration was reported by assessing the extent of Nissl‐stained infiltrates of the intact cerebral leptomeninges, and perivascular spaces from a minimum of 6 sampled blocks per case according to previously described criteria 34 . The extent of leptomeningeal inflammation was scored semiquantitatively as: absent = 0; mild (1); moderate (2); or substantial (3), to represent the largest single infiltrate observed for that case.…”

“…A combined measure of relative leptomeningeal and perivascular immune cell infiltration was reported by assessing the extent of Nissl-stained infiltrates of the intact cerebral leptomeninges, and perivascular spaces from a minimum of 6 sampled blocks per case according to previously described criteria. 34 The extent of leptomeningeal inflammation was scored semiquantitatively as: absent = 0; mild (1); moderate (2); or substantial (3), to represent the largest single infiltrate observed for that case.…”