SummaryThe immune system is highly diverse, but characterization of its genetic architecture has lagged behind the vast progress made by genome-wide association studies (GWASs) of emergent diseases. Our GWAS for 54 functionally relevant phenotypes of the adaptive immune system in 489 healthy individuals identifies eight genome-wide significant associations explaining 6%–20% of variance. Coding and splicing variants in PTPRC and COMMD10 are involved in memory T cell differentiation. Genetic variation controlling disease-relevant T helper cell subsets includes RICTOR and STON2 associated with Th2 and Th17, respectively, and the interferon-lambda locus controlling regulatory T cell proliferation. Early and memory B cell differentiation stages are associated with variation in LARP1B and SP4. Finally, the latrophilin family member ADGRL2 correlates with baseline pro-inflammatory interleukin-6 levels. Suggestive associations reveal mechanisms of autoimmune disease associations, in particular related to pro-inflammatory cytokine production. Pinpointing these key human immune regulators offers attractive therapeutic perspectives.
Increasing evidence implicates B cells in the pathogenesis of multiple sclerosis. Smets et al. report that the CD40 multiple sclerosis risk allele lowers CD40 expression, whereas the CD86 risk allele increases CD86 expression. B cells may have an important antigen presentation and immunoregulatory role in multiple sclerosis.
Objective Evidence for a role of microglia in the pathogenesis of multiple sclerosis (MS) is growing. We investigated association of microglial markers at time of diagnostic lumbar puncture (LP) with different aspects of disease activity (relapses, disability, magnetic resonance imaging parameters) up to 6 years later in a cohort of 143 patients. Methods In cerebrospinal fluid (CSF), we measured 3 macrophage and microglia‐related proteins, chitotriosidase (CHIT1), chitinase‐3–like protein 1 (CHI3L1 or YKL‐40), and soluble triggering receptor expressed on myeloid cells 2 (sTREM2), as well as a marker of neuronal damage, neurofilament light chain (NfL), using enzyme‐linked immunosorbent assay and electrochemiluminescence. We investigated the same microglia‐related markers in publicly available RNA expression data from postmortem brain tissue. Results CHIT1 levels at diagnostic LP correlated with 2 aspects of long‐term disease activity after correction for multiple testing. First, CHIT1 increased with reduced tissue integrity in lesions at a median 3 years later (p = 9.6E‐04). Second, CHIT1 reflected disease severity at a median 5 years later (p = 1.2E‐04). Together with known clinical covariates, CHIT1 levels explained 12% and 27% of variance in these 2 measures, respectively, and were able to distinguish slow and fast disability progression (area under the curve = 85%). CHIT1 was the best discriminator of chronic active versus chronic inactive lesions and the only marker correlated with NfL (r = 0.3, p = 0.0019). Associations with disease activity were, however, independent of NfL. Interpretation CHIT1 CSF levels measured during the diagnostic LP reflect microglial activation early on in MS and can be considered a valuable prognostic biomarker for future disease activity. ANN NEUROL 2020;87:633–645
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