CSF-Derived CD4+ T-Cell Diversity Is Reduced in Patients With Alzheimer Clinical Syndrome

Background and ObjectivesPatients with Alzheimer dementia display evidence of amyloid-related neurodegeneration. Our focus was to determine whether such patients also display evidence of a disease-targeting adaptive immune response mediated by CD4+ T cells. To test this hypothesis, we evaluated the CSF immune profiles of patients with Alzheimer clinical syndrome (ACS), who display clinically defined dementia.MethodsInnate and adaptive immune profiles of patients with ACS were measured using multicolor flow cytometry. CSF-derived CD4+ and CD8+ T-cell receptor repertoire genetics were measured using next-generation sequencing. Brain-specific autoantibody signatures of CSF-derived antibody pools were measured using array technology or ELISA. CSF from similar-age healthy controls (HCs) was used as a comparator cohort.ResultsInnate cells were expanded in the CSF of patients with ACS in comparison to HCs, and innate cell expansion increased with age in the patients with ACS, but not HCs. Despite innate cell expansion in the CSF, the frequency of total CD4+ T cells reduced with age in the patients with ACS. T-cell receptor repertoire genetics indicated that T-cell clonal expansion is enhanced, and diversity is reduced in the patients with ACS compared with similar-age HCs.DiscussionExamination of CSF indicates that CD4+ T cell–mediated adaptive immune responses are altered in patients with ACS. Understanding the underlying mechanisms affecting adaptive immunity will help move us toward the goal of slowing cognitive decline.

Antigen experience relaxes the organisational structure of the T cell receptor repertoire

The creation and evolution of the T cell receptor repertoire within an individual combines stochastic and deterministic processes. We systematically examine the structure of the repertoire in different T cell subsets in young, adult and LCMV infected mice, from the perspective of variable gene usage, nucleotide sequences and amino acid motifs. Young individuals share a high level of organization, especially in the frequency distribution of variable genes and amino acid motifs. In adult mice, this structure relaxes and is replaced by idiotypic evolution of the effector and regulatory repertoire. The repertoire of CD4+ regulatory T cells was more similar to naïve cells in young mice, but became more similar to effectors with age. Finally, we observed a dramatic restructuring of the repertoire following infection with LCMV. We hypothesize that the stochastic process of recombination and thymic selection initially impose a strong structure to the repertoire, which gradually relaxes following asynchronous responses to different antigens during life.