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- Bergström, Joakim, 1987-
(författare)
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A Search for the Masked Mechanism Behind IgG-Mediated Suppression of Antibody Responses
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Antibodies passively administered together with their specific antigen can enhance or suppress the specific antibody response. This phenomenon is known as antibody feedback regulation. Whether this modulation causes up- or downregulation of the antibody response depends both on the antibody isotype and the antigen used. IgG antibodies passively administered together with particulate antigens, e.g. erythrocytes, can completely prevent the induction of an antibody response to the antigen. The suppressive capacity of IgG has been routinely used in the clinic since the 1960’s in RhD-prophylaxis to prevent hemolytic disease of the fetus and newborn. Although studied for decades, the underlying mechanism of IgG-suppression has remained elusive. The main focus of this thesis has been to elucidate the mechanism behind IgG-suppression of antibody responses in vivo in mouse models using intravenous immunization with specific IgG together with native or haptenated sheep red blood cells, SRBC. We show that IgG-suppression of IgM and long-term serum IgG-responses operates independently of activating FcγRI, III, IV, or the inhibitory FcγRIIB, thus confirming and extending previous findings. Moreover, we demonstrate for the first time that C1q, C3 and CR1/2 are dispensable for IgG-suppression of antibody responses. These findings strongly argue against the involvement of Fc-dependent mechanisms as the explanation for IgG-suppression. Interestingly, GC formation occurs in IgG-suppressed mice although the antibody response to surface SRBC epitopes are completely suppressed. The data suggests that these GCs develop in response to intracellular SRBC epitopes as well as to the passively administered suppressive IgG. Moreover, we demonstrate that passively administered IgG suppresses several parameters of an antibody/B cell response including antigen specific GC and non-GC B cells, extra-follicular antibody secreting cells, long-lived plasma cells and induction of immunological memory. Before the onset of the present study, two mechanisms appeared compatible with the majority of experimental findings: IgG-mediated antigen clearance and epitope masking. Herein we show that the contribution of IgG-mediated antigen clearance is negligible and that suppression of IgG-responses is strictly epitope specific. This provides compelling evidence that a very important mechanism underlying IgG-suppression is epitope masking.
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| 2. |
- Rostami, Jinar, 1992-
(författare)
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The role of glial cells in alpha-synuclein pathology : Focus on degradation, cell-to-cell propagation and inflammation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Growing evidence emphasizes the role of astrocytes and microglia in Parkinson’s disease (PD) and Alzheimer’s disease (AD). Yet, little is known about their impact on specific disease processes and if their involvement is beneficial or detrimental. The aim of this thesis was to further investigate the role of astrocytes and microglia in PD and AD. To this purpose, cultured human astrocytes and microglia were exposed to aggregates of alpha-synuclein (αSYN) or amyloid-beta (Aβ), proteins that are central to PD and AD brain pathology, respectively.In Paper I, the toxicity and cell-to-cell spreading of aggregated αSYN in human astrocytes were evaluated. We found that astrocytes can engulf large amounts of αSYN aggregates, which are stored inside the cells instead of being degraded. This intracellular storage was found to result in severe cellular stress. As a response, stressed astrocytes were shown to transfer αSYN via tunneling nanotubes (TNT) to healthy astrocytes.T cells have been observed to enter the PD brain, but little is known about which stationary cell types they interact with. In Paper II, the ability of astrocytes and microglia to act as antigen presenting cells in the presence of aggregated αSYN was investigated. Both astrocytes and microglia were capable of expressing major histocompatibility class I (MHCI) and MHCII. However, only astrocytes had the capacity to express other molecules crucial for T-cell activation, such as CD80 and CD86. MHCII expressing astrocytes were also found in close vicinity to T cells in the PD brain.In paper III, the cross-talk between microglia and astrocytes in the presence of αSYN and Aβ aggregates was examined. When cultured separately, microglia appeared to degrade αSYN and Aβ better than astrocytes. However, co-culture experiments showed that microglia and astrocytes have a synergistic effect on the clearance of protein aggregates. Cell-to-cell contact was revealed as one of the possible mechanisms by which astrocytes and microglia communicate with each other.In Paper IV, the molecular mechanisms by which the compound KYP-2407 enhances αSYN clearance was investigated. We found that KYP-2407 stimulates the auto-lysosomal pathway in the presence of αSYN aggregates. Calpain proteins, which increase αSYN aggregation and diminish autophagy in PD, were also shown to be reduced in the presence of KYP-2407.Taken together, this thesis contributes with novel and important knowledge to the potential role of astrocytes and microglia in PD and AD.
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| 3. |
- Behere, Anish, 1993-
(författare)
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Ex‘PLA’ining the progression of pathological proteins in Alzheimer’s and Parkinson’s diseases : see(d)ing is believing
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the two most common forms of neurodegenerative disorders affecting approximately 50 million people worldwide. The underlying neuropathological processes leading to AD and PD share many similarities, i.e. aberrant protein aggregation of tau and alpha-synuclein (αSyn) in the brain. Monitoring tau and αSyn aggregation is challenging, due to morphological heterogeneity of the aggregating species and problems in preserving the antigen conformation ex vivo.In paper-I, we validated the usefulness of proximity ligation assay (PLA), a technique that enabled us to visualize previously undetected early αSyn pathology in the A30P-tg mouse model of PD. We observed an age-progressive increase in the levels of phosphorylated αSyn (pSynS129) and the compactness of aggregates in the brain. Although loss of dopaminergic neurons was not found, a subtle dysregulation of other catecholamines was recorded in the older mice.In paper-II, we revealed a wide distribution of pSynS129 aggregates in alpha-synucleinopathy-patient brains. By using a PLA setup with certain antibody pair combinations on brain sections, we observed unique staining patterns, which could not be visualized using regular immunohistochemistry (IHC). In A30P-tg mice, the morphological pattern of the PLA signals indicated an intracellular shift of pSynS129 from the periphery towards the neuronal soma.In Paper-III, we demonstrated that multiplex pTauS202,T205-pTauT231, singleplex pTauT231 and singleplex pSynS129 PLAs can recognize an extensive tau and αSyn pathology compared to regular IHC. We found that using our PLA approach we could differentiate between pTauS202,T205 and pTauT231 pathology in AD brains, whereas IHC could not. Similarly, in the PD brain, singleplex pSynS129 PLA detected novel structures, i.e. apparent thick intercellular tunnelling nanotubes and early aggregates; whereas pSynS129 IHC was limited to the detection of mature pathology. Lastly, we demonstrated that our multiplex PLA approach detected co-aggregates of pSynS129-pTau.In Paper-IV, in an αSyn seeding mouse model we observed pSynS129 immunoreactivity close to the striatal injection site one day post-injection (dpi). Intriguingly, this type of staining disappeared with the concurrent formation of peri-nuclear pSynS129 inclusions in specific brain regions after 14 dpi. In parallel, astrocytic activation prior to pSynS129 inclusion formation was observed.In conclusion, we have developed several novel PLAs that detect both tau and αSyn pathology with a higher ex vivo sensitivity and specificity than currently used immunostaining methods. This thesis work provides valuable insights that potentially could be used for the development of future biomarkers for tauopathies and synucleinopathies.
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| 4. |
- Bergh, Johan, 1983-
(författare)
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Structural investigation of SOD1 aggregates in ALS : identification of prion strains using anti-peptide antibodies
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative syndrome characterized by progressive degeneration of motor neurons that result in muscle wasting. The symptoms advance gradually to paralysis and eventually death. Most patients suffer from sporadic ALS (sALS) but 10% report a familial predisposition. Mutations in the gene encoding superoxide dismutase-1 (SOD1) were the first identified cause of ALS. The disease mechanism is debated but there is a consensus that mutations in this protein confer a cytotoxic gain of function. SOD1 aggregates in motor neurons are hallmarks of ALS both in patients and in transgenic mouse models expressing a mutated form of human SOD1 (hSOD1). Recently, our group showed that SOD1 aggregates are present also in sALS patients, thus indicating a broader involvement of this protein in ALS. Misfolding and aggregation of SOD1 are difficult to study in vivo since aggregate concentration in the central nervous system (CNS) is exceedingly low. The aim of this thesis was to find a method circumventing this problem to investigate the hSOD1 aggregate structure, distribution and spread in ALS disease.Many studies provide circumstantial evidence that the wild-type hSOD1 protein can be neurotoxic. We developed the first homozygous mouse model that highly overexpresses the wild-type enzyme. These mice developed an ALS-like syndrome and become terminally ill after around 370 days. Motor neuron loss and SOD1 aggregate accumulation in the CNS were observed. This lends further support to the hypothesis of a more general involvement of SOD1 in human disease.A panel of polyclonal antibodies covering 90% of the SOD1 protein was developed by our laboratory. These antibodies were shown to be highly specific for misfolded SOD1. Aggregated hSOD1 was purified from the CNS of terminally ill hSOD1 mice. Disordered segments in aggregated hSOD1 could be identified with these antibodies. Two aggregate strains with different structural architectures, molecular properties, and growth kinetics, were found using this novel method. The strains, denoted A and B, were also associated with different disease progression. Aggregates formed in vitro were structurally different from these strains. The results gave rise to questions about aggregate development and possible prion-like spread. To investigate this, inoculations of purified strain A and B hSOD1 seeds was performed in lumbar spinal cords of 100-day old mice carrying a hSOD1G85R mutation. Mice seeded with A or B aggregates developed premature signs of ALS and became terminally ill 200 days earlier than mice inoculated with control preparation. Interestingly, a templated spread of aggregates along the neuraxis was concomitantly observed, with strain A and B provoking the buildup of their respective hSOD1 aggregate structure. The phenotypes initiated by the A and B strains differed regarding progression rates, distribution, end-stage aggregate levels, and histopathology. To further establish the importance of hSOD1 aggregates in human disease, purification and inoculation of aggregate seeds from spinal cords of ALS patients and mice carrying the hSOD1G127X mutation were performed. Inoculation of both human and mouse seeds as described above, induced strain A aggregation and premature fatal ALS-like disease.In conclusion, the data presented in this thesis provide a new, straightforward method for characterization of aggregate strains in ALS, and plausibly also in other neurodegenerative diseases. Two different prion strains of hSOD1 aggregates were identified in mice that resulted in ALS-like disease. Emerging data suggest that prion-like growth and spread of hSOD1 aggregation could be the primary pathogenic mechanism not only in hSOD1 transgenic models, but also in human ALS.
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