Investigating the neuroimmunogenic architecture of schizophrenia
The role of the immune system in schizophrenia remains controversial despite numerous studies to date. Most studies have profiled expression of select genes or proteins in peripheral blood, but none have focused on the expression of canonical pathways that mediate overall immune response. The current study used a systematic genetic approach to investigate the role of the immune system in a large sample of post-mortem brain of patients with schizophrenia: RNA sequencing was performed to assess the differential expression of 561 immune genes and 20 immune pathways in dorsolateral prefrontal cortex (DLPFC) (144 schizophrenia and 196 control subjects) and hippocampus (83 schizophrenia and 187 control subjects). The effect of RNA quality on gene expression was found to be highly correlated with the effect of diagnosis even after adjustment for observable RNA quality parameters (i.e. RNA integrity), thus this confounding relationship was statistically controlled using principal components derived from the gene expression matrix. In DLPFC, 23 immune genes were found to be differentially expressed (false discovery rate < 0.05), of which seven genes replicated in both directionality and at nominal significance (P < 0.05) in an independent postmortem DLPFC data set (182 schizophrenia and 212 control subjects), although notably at least five of these genes have prominent roles in pathways other than immune function and overall the effect sizes were minimal (fold change < 1.1). In the hippocampus, no individual immune genes were identified to be differentially expressed, and in both DLPFC and hippocampus none of the individual immune pathways were relatively differentially expressed. Further, genomic schizophrenia risk profiles scores were not correlated with the expression of individual immune pathways or differentially expressed genes. Overall, past reports claiming a primary pathogenic role of the immune system intrinsic to the brain in schizophrenia could not be confirmed.