Clonally expanded plasma cells (cePC) and their presumed products, oligoclonal immunoglobulin G bands (OCB), are characteristic findings in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS). While cePC and OCB strongly suggest an involvement of B cell-dependent immune mechanisms in the pathogenesis of MS, their actual pathological relevance and target antigens remain unknown. To further understand the potential role played by cePC, we generated a panel of monoclonal antibodies (MS-mAb) from CSF-derived cePC from four patients with early or definite MS. Single-cell RT-PCR of correctly paired heavy and light chain immunoglobulin genes from individual cePC ensured the subsequent resurrection of their original antigen specificity. Immunofluorescence stainings of MS lesion tissue with MS-mAb revealed myelin reactivity in the cePC repertoire of all four patients and intracellular filament reactivity in one patient. While myelin staining by MS-mAb was only rarely detectable in non-MS CNS white matter tissue, it was greatly enhanced at the edge of demyelinating lesions in MS brain tissue. Our findings provide conclusive evidence for the presence of an antigen-driven B cell response in the CSF of MS patients directed against epitopes present in areas of myelin degradation.

Permanent disability of patients suffering from central nervous system (CNS) inflammation such as multiple sclerosis, the most common chronic inflammatory disorder of the CNS, originates mainly from demyelination and axonal damage. Although many studies in the past focused on the role of CD4 ؉ T cells, several recent findings postulate the relevance of autoaggressive, cytotoxic CD8 ؉ T cells in the effector phase of multiple sclerosis. Yet, it remains unresolved whether axonal injury is the result of a CD8 ؉ T cell-targeted hit against the axon itself or the consequence of an attack against the myelin structure. To address this issue of CD8-mediated tissue damage in CNS inflammation , we performed continuous confocal imaging of autoaggressive , cytotoxic CD8 ؉ T cells in living organotypic cerebellar brain slices. We observed that loading brain slices with the cognate peptide antigen caused CD8-mediated damage of myelinated axons. To exclude the possibility that the cognate peptide loaded onto the brain slices was presented by axons directly , we restricted the cognate antigen expression exclusively to the cytosol of oligodendrocytes. Aside from vast myelin damage , extensive axonal bystander injury occurred. Using this model system of inflammatory CNS injury , we visualize that axonal loss can be the consequence from "collateral bystander damage" by autoaggressive , cytotoxic CD8 ؉ T cells , targeting their cognate antigen processed and presented by oligodendrocytes.

Neuroborreliosis (NB) is a chronic infectious disease of the central nervous system (CNS) caused by a tick-borne spirochete, Borrelia burgdorferi. In addition to direct effects of the causative infectious agent, additional immunity-mediated mechanisms are thought to play a role in the CNS pathology of NB. In order to further understand the involvement of humoral immune mechanisms in NB, we dissected the intrathecal antibody responses down to the single-plasma-cell level. Starting with single-cell reverse transcription-PCR of fluorescence-activated cell sorter-sorted cerebrospinal fluid plasma cells from an NB patient, we identified expanded clones and resurrected the antigen specificity of their secreted antibodies through recombinant expression of the correctly paired immunoglobulin heavy-and light-chain genes as monoclonal antibodies (MAbs). As expected, we found specificity for the causative infectious agent, B. burgdorferi, among the clonally expanded plasma cell (cePC)-derived MAbs. However, from an independent cePC of the same patient, we could derive MAbs specific for human CNS myelin, without detectable cross-reactivity with B. burgdorferi antigens. While reactivity against B. burgdorferi is a known feature of humoral immune responses in NB, we show (i) that immune responses specific for self antigens may be a distinct feature of CNS infections independent of pathogen reactivity and (ii) that humoral autoimmunity in NB (since found in cePC) is the result of a truly antigen-driven immune response. Our findings indicate that in NB mechanisms may be at play that induce distinct immune responses specific for pathogen and self antigens independent from "molecular mimicry

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The cover shows a confocal micrograph of myelinated nervous tissue at the rim of a demyelinating lesion in the brain white matter of a patient with multiple sclerosis (MS). Myelin surrounding the axon is stained by a monoclonal antibody obtained by recombinant expression of immunoglobulin genes from clonally expanded plasma cells as present in the cerebrospinal fluid of MS patients. The image was taken from the article by von Büdingen et al. (pp. in which the authors demonstrate that myelin specific antibodies result from antigen driven immune responses found in the cerebrospinal fluid of MS patients.