Abstract
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.MethodsWe 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).ResultsWe 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.InterpretationBecause 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.
Highlights
Annals of Clinical and Translational Neurology published by Wiley Periodicals, Inc on behalf of American Neurological Association
Our strategy was based on the assumption that a cytotoxic CD8+ T cell is surrounded by many cells of different type and that the vectorial orientation of cytotoxic granules in the T cell will indicate the direction of its cellular communication partner
To identify the communication partners of CD8+ T cells in multiple sclerosis (MS) brain lesions, we developed an unbiased strategy that uses vectorial perforin orientation in T cells as guidepost for localizing their target cells without the need to visualize the targets directly
Summary
Lymphocyte infiltrations into the central nervous system (CNS) are observed in all patients with acute and chronic forms of multiple sclerosis (MS).[1,2,3,4] Decades ago it was found that the most prevalent lymphocyte population in MS lesions are CD8+ T cells[5,6] and this was recently confirmed in much more detail in large cohorts.[7,8,9] CD8+ T cells are present at perivascular sites and in the parenchyma of all patients regardless of the disease course,[3] are often clonally expanded,[8,10,11,12] may accumulate in clusters,[13] and distinct expanded clones may be found in different lesions and in normal appearing white matter.[7,12] Many of the infiltrating T cell clones show the antigen-experienced, tissue-resident, memory phenotype.[7,9,13] This suggests that they are involved in the pathogenesis, but so far it is unknown with which target cells they communicate within the lesions.Specific interactions of individual cells in tightly packed tissues are experimentally difficult to investigate because each cell is usually surrounded by many other cells. In MS, these challenges cumulate: many different cell types are tightly packed in the CNS and some of them have irregular shapes and long extensions (e.g., neurons, astrocytes, oligodendrocytes).[3,14] many brain-resident cells are of the mononuclear phagocyte (MP) lineage, which contains many subtypes of high plasticity (e.g., macrophages, microglia, monocytes).
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