Human intravenous immunoglobulin provides protection against A? toxicity by multiple mechanisms in a mouse model of Alzheimer's disease.
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ABSTRACT: BACKGROUND: Purified intravenous immunoglobulin (IVIG) obtained from the plasma of healthy humans is indicated for the treatment of primary immunodeficiency disorders associated with defects in humoral immunity. IVIG contains naturally occurring auto-antibodies, including antibodies (Abs) against ?-amyloid (A?) peptides accumulating in the brains of Alzheimer's disease (AD) patients. IVIG has been shown to alleviate AD pathology when studied with mildly affected AD patients. Although its mechanisms-of-action have been broadly studied, it remains unresolved how IVIG affects the removal of natively formed brain A? deposits by primary astrocytes and microglia, two major cell types involved in the neuroinflammatory responses. METHODS: We first determined the effect of IVIG on A? toxicity in primary neuronal cell culture. The mechanisms-of-action of IVIG in reduction of A? burden was analyzed with ex vivo assay. We studied whether IVIG solubilizes natively formed A? deposits from brain sections of APP/PS1 mice or promotes A? removal by primary glial cells. We determined the role of lysosomal degradation pathway and A? Abs in the IVIG-promoted reduction of A?. Finally, we studied the penetration of IVIG into the brain parenchyma and interaction with brain deposits of human A? in a mouse model of AD in vivo. RESULTS: IVIG was protective against A? toxicity in a primary mouse hippocampal neuron culture. IVIG modestly inhibited the fibrillization of synthetic A?1-42 but did not solubilize natively formed brain A? deposits ex vivo. IVIG enhanced microglia-mediated A? clearance ex vivo, with a mechanism linked to A? Abs and lysosomal degradation. The IVIG-enhanced A? clearance appears specific for microglia since IVIG did not affect A? clearance by astrocytes. The cellular mechanisms of A? clearance we observed have potential relevance in vivo since after peripheral administration IVIG penetrated to mouse brain tissue reaching highest concentrations in the hippocampus and bound selectively to A? deposits in co-localization with microglia. CONCLUSIONS: Our results demonstrate that IVIG promotes recognition and removal of natively formed brain A? deposits by primary microglia involving natural A? Abs in IVIG. These findings may have therapeutic relevance in vivo as IVIG penetrates through the blood-brain barrier and specifically binds to A? deposits in brain parenchyma.
SUBMITTER: Magga J
PROVIDER: S-EPMC3004875 | biostudies-literature | 2010
REPOSITORIES: biostudies-literature
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