ABSTRACT
Recent studies have described significant demyelination and microglial activation in the cerebral cortex of brains from multiple sclerosis patients. To date, however, experimental models of cortical demyelination or cortical inflammation have not been extensively studied. In this report we describe focal cortical inflammation induced by stereotaxic injection of killed bacteria (BCG), followed 1 month later by subcutaneous injection of the same antigen, a protocol that overcomes the immune privilege of the cortex. Intracerebral BCG injection produced focal microglial activation at the injection site (termed acute lesion). Ten days after peripheral challenge (termed immune-mediated lesion), larger areas and higher densities of activated microglia were found near the injection site. In both paradigms, activated microglia and/or their processes closely apposed neuronal perikarya and apical dendrites. In the immune-mediated lesions, approximately 45% of the axosomatic synapses was displaced by activated microglia. Upon activation, therefore, cortical microglial migrate to and strip synapses from neuronal perikarya. Since neuronal pathology was not a feature of either the acute or immune-mediated lesion, synaptic stripping by activated microglia may have neuroprotective consequences.
Subject(s)
Cerebral Cortex/physiology , Microglia/physiology , Synapses/physiology , Animals , BCG Vaccine/immunology , BCG Vaccine/toxicity , Cerebral Cortex/cytology , Cerebral Cortex/metabolism , Chemokine CCL2/metabolism , Fluorescent Antibody Technique , Freund's Adjuvant/pharmacology , Immunohistochemistry , Inflammation/chemically induced , Male , Microglia/metabolism , Microscopy, Confocal , Microscopy, Electron , Rats , Rats, Inbred Lew , Synapses/metabolismABSTRACT
Specific chemokines and chemokine receptors have been implicated in inflammatory demyelinating diseases of the central nervous system (CNS), including multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). Amino-terminal modifications of chemokines can alter receptor interactions, converting agonists to specific antagonists. To examine the function in EAE of murine types 1 and 5 CC chemokine receptors (CCR1 and CCR5), we used Met-RANTES, a peptide that blocks both receptors; controls received heat-inactivated peptide. There was no effect of active treatment on acute-monophasic EAE, regardless whether compound was given at onset or in a pre-treatment regimen. Administered at disease onset, Met-RANTES modestly but significantly ameliorated fixed neurological disability at the endpoint of chronic-relapsing EAE. Met-RANTES treatment did not reduce CNS cellular infiltrates or up-regulation of CCR1 and CCR5 in affected CNS tissues. Analysis of a subset of mice suggested a trend towards reduced axonal pathology in those receiving active treatment. These data indicate that chemokine receptor blockade with Met-RANTES does not affect leukocyte trafficking in chronic-relapsing EAE. Further analysis of the effects of chemokine receptor blockade may need to focus on leukocyte activation within the affected CNS as well as trafficking events.
Subject(s)
Chemokine CCL5/analogs & derivatives , Chemokine CCL5/pharmacology , Chemokines/antagonists & inhibitors , Encephalomyelitis, Autoimmune, Experimental/drug therapy , Multiple Sclerosis/drug therapy , Receptors, Chemokine/antagonists & inhibitors , Spinal Cord/drug effects , Animals , Axons/drug effects , Axons/immunology , Axons/pathology , Chemokine CCL5/therapeutic use , Chemokines/immunology , Chemokines/metabolism , Chemotaxis, Leukocyte/drug effects , Chemotaxis, Leukocyte/immunology , Encephalomyelitis, Autoimmune, Experimental/immunology , Encephalomyelitis, Autoimmune, Experimental/pathology , Female , Glyceraldehyde-3-Phosphate Dehydrogenases/metabolism , Mice , Mice, Inbred C57BL , Multiple Sclerosis/immunology , Multiple Sclerosis/pathology , RNA, Messenger/drug effects , RNA, Messenger/immunology , RNA, Messenger/metabolism , Receptors, CCR1 , Receptors, CCR5/genetics , Receptors, Chemokine/genetics , Receptors, Chemokine/immunology , Receptors, Chemokine/metabolism , Spinal Cord/immunology , Spinal Cord/pathology , Treatment FailureABSTRACT
Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). Most patients undergo an initial relapsing-remitting (RR-MS) course that transforms into a relentless neurodegenerative disorder, termed secondary progressive (SP)-MS. Reversible inflammation and demyelination account readily for the pattern of RR-MS but provide an unsatisfactory explanation for irrevocable decline in SP-MS. Axon loss is thought to be responsible for progressive, non-remitting neurological disability during SP-MS. There is considerable potential for neuroprotective therapies in MS, but their application awaits animal models in which axonal loss correlates with permanent neurological disability. In this report, we describe quantitative immunohistochemical methods that correlate inflammation and axonal loss with neurological disability in chronic-relapsing experimental autoimmune encephalomyelitis (EAE). At first attack, CNS inflammation, but not axon loss, correlated with the degree of neurological disability. In contrast, fixed neurological impairment in chronic EAE correlated with axon loss that, in turn, correlated with the number of symptomatic attacks. As proposed for MS, these observations imply a causal relationship between inflammation, axon loss, and irreversible neurological disability. This chronic-relapsing EAE model provides an excellent platform for 2 critical objectives: investigating mechanisms of axon loss and evaluating efficacy of neuroprotective therapies.
