Complement Activation In The Parkinson S Disease Substantia Nigra An Immunohistochemical Study1/22/2017 Microglial inflammation in the parkinsonian substantia nigra: relationship to alpha- synuclein deposition. Abstract. Background. The role of both microglial activation and alpha- synuclein deposition in Parkinson's disease remain unclear. We have tested the hypothesis that if microglia play a primary role in Parkinson's disease pathogenesis, the microglial "activated" phenotype should be associated with histopathological and/or clinical features of the disease. Methods. We have examined microglial MHC class II expression, a widely used marker of microglial activation, the occurrence of CD6. Parkinson's disease (PD). Using semi- quantitative severity ratings, we have examined the relationship between microglial activation, alpha- synuclein deposition, classical neuropathological criteria for PD, subtype of the disease and clinical course. Results. While we did not observe an association between microglial MHC class II expression and clinical parameters, we did find a correlation between disease duration and the macrophage marker CD6. In addition, we observed a significant correlation between the degree of MHC class II expression and alpha- synuclein deposition in the substantia nigra in PD. Conclusion. While microglia appeared to respond to alpha- synuclein deposition, MHC class II antigen expression by microglia in the substantia nigra cannot be used as an indicator of clinical PD severity or disease progression. . (MPTP). Immunohistochemical staining of dopaminergic neurons in. there is still a possibility that MPTP-induced complement activation does not. Complement activation in the Parkinson's disease substantia nigra.![]() ![]() In addition, a contributory or even causative role for microglia in the neuronal loss associated with PD as suggested by some authors seems unlikely. Our data further suggest that an assessment of microglial activation in the aged brain on the basis of immunohistochemistry for MHC class II antigens alone should be done with caution. Introduction. Parkinson's Disease (PD) is a common neurodegenerative disorder with the cardinal clinical features of tremor, rigidity, bradykinesia and loss of postural reflexes. Neuropathologically, the disease is characterized by a marked loss of dopaminergic neurons in the substantia nigra pars compacta (SN) and the presence of alpha- synuclein (a. SN)- positive Lewy bodies (LBs) in neurons of this and other brain areas also affected by nerve cell death. Plaque Complement Activation and Cognitive Loss in Alzheimer's Disease. Complement activation in the Parkinson's disease substantia nigra: an immunocytochemical study. J Neuroinflammation 2006. Relationship between microglial activation and dopaminergic neuronal loss in the substantia nigra: a time course study in a. Parkinson’s disease. SNc. substantia nigra. neuronal loss and activation of. An international consensus definition of Lewy body diseases on the basis of molecular as well as morphological criteria, which takes into account a. SN status of the brain, has been published recently http: //www. ICDNS. org[1]. The discovery of a. SN mutations and gene amplification in some familial forms of PD [2- 6]] and the identification of this protein as a major component of Lewy bodies (LBs) in common sporadic PD [7], has spurred interest in the role of a. SN in the pathophysiology of PD and other synucleinopathies. However, no direct causal relationship has yet been established between a. SN aggregation and the selective neuronal cell death characteristic of PD. LBs are also found incidentally in aged brain in the absence of other pathological features and without a clinical history of parkinsonism or dementia [8]. Attempts have been made to link the clinical progression of PD to the presence of a. SN inclusions and an anatomical staging model has been proposed [9], but the latter has been questioned by subsequent studies in which clinical data were also taken into account [1. ![]()
Apart from well established morphological criteria, activated microglia can be defined in tissue sections on the basis of the expression of several immune function- related proteins, notably complement receptors and MHC class II antigens (MHCII). Phagocytic activity and cytotoxic properties are usually considered end stages of microglial activation, at which point they are phenotypically indistinguishable from blood- borne macrophages. Activated microglia are associated with a large range of neurological insults from trauma and infection to autoimmune conditions, and their presence represents a common finding also in neurodegenerative disorders [1. ![]() ![]() However there is little knowledge about the molecular processes that mediate microglial activation and exactly which biological consequences may result from their enhanced state of "immune alertness" within affected CNS tissue. A transcriptome signature of interferon- gamma activated microglia has been provided recently [1. Microglial phenotypic changes have also been observed in normal aged individuals [1. Thus, "microglial senescence" confounds the problem of a definition of microglial activation in disease states, and in neurodegenerative diseases in particular which are often age- related, as no specific causative stimulus has been identified in the process. While microglia clearly show changes in their phenotypic profile in neurodegeneration, it is by no means clear whether they are actively involved in the progression of PD. Microglia- derived macrophages can be found in the PD SN, and neuromelanin pigment taken up from degenerated dopaminergic nerve cells is characteristically observed in SN phagocytes. In animal models of nigrostriatal degeneration using 6- hydroxydopamine and 1- methyl- 4- phenyl- 1,2,3,6- tetrahydropyridine (MPTP), inhibition or attenuation of the microglial immune response increases neuronal survival. However, those results have so far not been replicated in clinico- pathological studies, and the simple chemical lesions currently employed in animal studies by all likelihood do not fully reflect the chronic neurodegenerative disease process in humans [1. In the present study, we independently evaluate the severity of alpha- synuclein deposition and microglial activation identified by immunohistochemical staining in the SN in a large cohort of clinically and pathologically confirmed PD cases. We have studied the microglial response in PD on two levels, by observing MHCII - immunoreactive cells (putatively activated microglia but possibly only senescent cells) and CD6. Materials and methods. Parkinson's disease cases. PD nigrae were evaluated immunohistochemically. UK Parkinson's Disease Society Tissue Bank at Imperial College London (PDSTB). Additional tissue sections from 1. Institute of Neuropathology, University of Munich, Germany. These Parkinson's cases had been previously diagnosed, neuropathologically screened for confounding pathology, and examined in a study of apoptosis and microglial activation [1. Archival sections were immunolabelled for alpha- synuclein (see below) and used as a control group to ensure that variation within our PDSTB cohort was within an established range. Clinical and neuropathological assessment of cases. For the PDSTB cohort, clinical reports were evaluated in detail by an experienced neurologist with a special interest in Parkinson's disease (RKBP). Neuropathological assessment was based on slides provided by the PDSTB for alpha- synuclein, tau and beta- amyloid immunohistochemistry of superior frontal gyrus, the hippocampal region and midbrain as minimum data sets, and screening of the cases for confounding pathology was based on hematoxylin and eosin examination of a standard series of 1. Nine cases showed varying degrees of concurrent Alzheimer's disease (AD)- type pathology (tau- immunopositive tangles and/or beta- amyloid- immunopositive plaques) of isocortical and/or entorhinal type ranging from grades 1–3 http: //www. ICDNS. org. Three cases were excluded based on a final neuropathological diagnosis of AD, progressive supranuclear palsy (PSP), and young- onset familial PD, respectively, leaving a cohort of 1. Munich and PDSTB groups (Table 1). Immunohistochemical evaluation of protein levels. Immunohistochemical reactions were performed using the avidin- biotin complex (ABC)/peroxidase method with mouse monoclonal antibodies anti- human HLA- DP, DQ, DR (clone CR3/4. Dako, dilution 1/1. Becton- Dickinson, dilution 1/3. For the PDSTB group, additional immunohistochemistry was carried out with anti- CD6. PGM1, Dako, dilution 1/2. Sections were dewaxed in xylene, rehydrated, and endogenous peroxidase activity was blocked by 3. Antigen unmasking consisted of boiling in 0. M EDTA (2. 0 min. W in microwave) and 1. HLA- DP, DQ, DR and anti- alpha- synuclein, respectively. No antigen unmasking was used with anti- CD6. Slides were then incubated in primary antibody diluted in phosphate- buffered saline (PBS) overnight at 4°C. The following day, after washing in PBS, they were incubated in horse- anti- mouse secondary antibody (Vector, dilution 1/2. ABC complex (Vector, dilution 1/2. Immunoreactivity was visualised with 3,3'- diaminobenzidine (Vector kit). After immunohistochemical staining, sections were given semi- quantitative severity ratings for a. SN, MHCII, and CD6. EC and MBG) blinded to case number. The SN was defined as the area extending laterally from the exit of the third nerve, superior to the cerebral peduncle and inferior to the medial lemniscus, ideally at the height of the red nucleus with the presence of melanised neurons or their remnants indicating the main region of interest. The severity ratings were determined across the entire region of SN, based on the density of immunopositive structures, with 0 (none), 1 (mild), 2 (moderate) and 3 (high). For a. SN, both intra- and extra- cellular inclusions were considered provided they fell within the immediate area of the substantia nigra. This was particularly relevant in areas of severe neuronal loss, often encountered more laterally, where significant alpha- synuclein pathology could still be observed. The morphological variation in a. SN deposition was not assessed, simply the frequency of events. All clearly identifiable a. SN- immunoreactive structures, including LBs, neurites, fibrils, and smaller, punctate formations, were considered. For microglial response, severity was judged primarily by immunoreactivity, however morphology was taken into account in that perivascular immunoreactivity was excluded.
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