The phagocytic capacity of neurones.

Phagocytosis is defined as the ingestion of particulates over 0.5 microm in diameter and is associated with cells of the immune system such as macrophages or monocytes. Neurones are not generally recognized to be phagocytic. Using light, confocal, time-lapse and electron microscopy, we carried out a wide range of in-vitro and in-vivo experiments to examine the phagocytic capacity of different neuronal cell types. We demonstrated phagocytosis of material by neurones, including cell debris and synthetic particles up to 2.8 microm in diameter. We showed phagocytosis in different neuronal types, and demonstrated that debris can be transported from neurite extremities to cell bodies and persist within neurones. Flow cytometry analysis demonstrated the lack of certain complement receptors on neurones but the presence of others, including integrin receptors known to mediate macrophage phagocytosis, indicating that a restricted set of phagocytosis receptors may mediate this process. Neuronal phagocytosis occurs in vitro and in vivo, and we propose that this is a more widespread and significant process than previously recognized. Neuronal phagocytosis may explain certain inclusions in neurones during disease, cell-to-cell spread of disease, neuronal death during disease progression and provide a potential mechanism for therapeutic intervention through the delivery of particulate drug carriers.

Activation of microglia in mice spinal cords following passive transfer of purified IgG from patients with amyotrophic lateral sclerosis.

OBJECTIVE: To determine whether IgG from amyotrophic lateral sclerosis (ALS) patients could cause activation of microglia, proliferation of astrocytes, and infiltration by lymphocytes within mice spinal cords. METHODS: A group of 5 mice received injections of IgG purified from sera of patients with ALS. A control group of 5 mice received IgG from healthy humans, whilst a third group of 2 mice served as non-injected controls. One mouse served as a positive control and was injected with lipopolysaccharide, a known activator of microglia. Mice were culled after one week, for immunocytochemistry of spinal cord sections to localize the complement receptor CD11b on activated microglia, glial fibrillary acidic protein on astrocytes, and CD4 and CD8 receptors on lymphocytes. Histological examination was used to determine the presence of inflammatory reaction. This work was conducted at the Institute of Neurology, Queen Square London, United Kingdom, from January to July 2004. RESULTS: There was no significant difference in activation of microglia between mice injected with ALS IgG and mice injected with control IgG (p = 0.631), although mice injected with ALS IgG exhibited greater microglial activation than non-injected mice (p = 0.044). Proliferation of astrocytes was not significantly different between the 3 groups. CD4 and CD8 lymphocytes were both absent in mice injected with ALS IgG, mice injected with control IgG and non-injected mice. CONCLUSION: Activation of microglia following passive transfer of IgG from ALS patients to mice represents a non-specific inflammatory response, rather than a primary mechanism for motor neuron degeneration.

Reduced neuronal nitric oxide synthase (NOS1) antigen in sacral motor neurones in motor neurone disease.

Immunocytochemistry and microdensitometry applied under standardised conditions were used to evaluate neuronal nitric oxide synthase (NOS1) antigen in segmental motor neurones (MN) of six subjects without neurological disease, nine subjects with sporadic motor neurone disease (MND) and five with neurological disease unrelated to MND. No significant segmental differences in levels of NOS1 immunoreactivity occurred between the two control groups, and differences between cervical, thoracic and lumbar MN of the three subject groups were not significant. However, MND patients showed a significantly reduced level of NOS1 immunoreactivity in the Onuf's nucleus (ON); this is discussed in relation to neuroprotection and the relative sparing of ON in MND.