Methylation profiles in peripheral blood CD4+ lymphocytes versus brain: The relation to Alzheimer's disease pathology.

INTRODUCTION: We investigated the change in DNA methylation in peripheral blood CD4+ lymphocytes over time, examined the relation between CD4+ lymphocytes and brain methylation, and compared their associations with AD pathology.

METHODS: Genome-wide methylation was measured three times in 41 older persons using Illumina Infinium HumanMethylation450 array. The two CD4+ lymphocytes measures were at study baseline and proximate to death. Brain tissue came from frozen dorsolateral prefrontal cortex.

RESULTS: Global methylation features were conserved across tissue. At individual CpG sites, methylation level was concordant between the two CD4+ lymphocytes but more diffuse between CD4+ lymphocytes and brain. Previous associations of brain methylation with neuritic plaques at target methylation sites were not replicated in CD4+ lymphocytes.

DISCUSSION: There is no strong evidence of change in CD4+ lymphocytes methylation among older persons over an average of 7.5 years. Methylation associations with AD pathology found in neocortex are not directly reflected in CD4+ lymphocytes.