Polarization of the Effects of Autoimmune and Neurodegenerative Risk Alleles in Leukocytes

Immunogenetic Variation Many genetic variants have been implicated in disease but their effects in function across tissues and cell-types remain to be resolved. Raj et al. (p. 519) present an analysis of expression quantative trait loci (eQTL) measuring messenger RNA levels and examined correlations between genotypes and gene expression in purified monocytes and T cells in healthy individuals of European, African, and Asian descent. Most, but not all, of the eQTLs and their effects on expression were shared between the populations, as well as a substantial proportion between the cell types. Links were found with disease-associated variants and loci that previous genome-wide analyses have implicated in neurodegenerative and autoimmune diseases. Genetic variants affecting gene expression show both shared and specific immune cell type effects. To extend our understanding of the genetic basis of human immune function and dysfunction, we performed an expression quantitative trait locus (eQTL) study of purified CD4+ T cells and monocytes, representing adaptive and innate immunity, in a multi-ethnic cohort of 461 healthy individuals. Context-specific cis- and trans-eQTLs were identified, and cross-population mapping allowed, in some cases, putative functional assignment of candidate causal regulatory variants for disease-associated loci. We note an over-representation of T cell–specific eQTLs among susceptibility alleles for autoimmune diseases and of monocyte-specific eQTLs among Alzheimer’s and Parkinson’s disease variants. This polarization implicates specific immune cell types in these diseases and points to the need to identify the cell-autonomous effects of disease susceptibility variants.