Communication of CD8+ T cells with mononuclear phagocytes in multiple sclerosis.

OBJECTIVE: CD8+ T cells are the most prevailing lymphocyte population in inflammatory lesions of patients with multiple sclerosis (MS) but it is not even known whether they are merely passive bystanders or actively communicate with other cells in the brain. To identify their potential interaction partners, we analyzed CD8+ T cells that contained vectorially oriented cytotoxic granules and analyzed the areas to which the granules pointed. METHODS: We stained cryo-sections of active MS lesions of an index patient with antibodies to CD8 and perforin, searched for vectorially oriented perforin granules, and isolated target areas opposing the granules and control areas by laser-microdissection. From both areas, we analyzed cell-type specific transcripts by next-generation sequencing. In parallel, we stained samples from the index-patient and other patients by four-color immunohistochemistry (IHC). RESULTS: We found transcripts of the mononuclear phagocyte (MP) specific markers CD163 and CD11b only in the microdissected target areas but not in control areas. We validated the finding that MPs are communication partners of CD8+ T cells in MS lesions by classical IHC in samples from the index-patient and other patients with acute and progressive MS and other inflammatory neurological diseases. INTERPRETATION: Because CD163 and CD11b are specifically expressed in MPs, our findings suggest that CD8+ T cells communicate with local MPs. Although it is still unclear if these interactions lead to killing of the communication partners by CD8+ T cells, our data underline that CD8+ T cells play an active role in the pathogenesis of MS.

Multiple sclerosis: Molecular mimicry of an antimyelin HLA class I restricted T-cell receptor.

OBJECTIVE: To identify target antigens presented by human leukocyte antigen (HLA)-A*02:01 to the myelin-reactive human T-cell receptor (TCR) 2D1, which was originally isolated from a CD8+ T-cell clone recognizing proteolipid protein (PLP) in the context of HLA-A*03:01, we employed a new antigen search technology. METHODS: We used our recently developed antigen search technology that employs plasmid-encoded combinatorial peptide libraries and a highly sensitive single cell detection system to identify endogenous candidate peptides of mice and human origin. We validated candidate antigens by independent T-cell assays using synthetic peptides and refolded HLA:peptide complexes. A molecular model of HLA-A*02:01:peptide complexes was obtained by molecular dynamics simulations. RESULTS: We identified one peptide from glycerolphosphatidylcholine phosphodiesterase 1, which is identical in mice and humans and originates from a protein that is expressed in many cell types. When bound to HLA-A*02:01, this peptide cross-stimulates the PLP-reactive HLA-A3-restricted TCR 2D1. Investigation of molecular details revealed that the peptide length plays a crucial role in its capacity to bind HLA-A*02:01 and to activate TCR 2D1. Molecular modeling illustrated the 3D structures of activating HLA:peptide complexes. CONCLUSIONS: Our results show that our antigen search technology allows us to identify new candidate antigens of a presumably pathogenic, autoreactive, human CD8+ T-cell-derived TCR. They further illustrate how this TCR, which recognizes a myelin peptide bound to HLA-A*03:01, may cross-react with an unrelated peptide presented by the protective HLA class I allele HLA-A*02:01.