Migration, psychosis and immune activation: A pilot study

Background: The risk for psychotic disorders is increased for many immigrant groups in several countries, particularly for those who migrated in early life and for second-generation immigrants. Social factors are likely to contribute to this increase, but biological pathways have hardly been explored. Since immune activation has been associated both with schizophrenia and social stress in early life, it may be involved in the pathway of migration, ethnic minority status and psychosis. Methods: Case-control study of 11 Dutch and 14 immigrant patients with first episode psychosis, and 14 Dutch and 10 immigrant healthy controls. Quantitative polymerase chain reaction (Q-PCR) techniques were used to measure mRNA levels of 97 genes in isolated monocytes. These genes were selected for their association with schizophrenia, bipolar disorder, autoimmune or inflammatory disorders in previous genome wide association studies. Results: Compared to Dutch controls, 29 genes in monocytes of Dutch cases were upregulated (fold changes more than two standard deviations (sd)) and statistical significance was reached for 13 genes. Most of these genes are involved in inflammation pathways, including coding for the pro-inflammatory cytokines IL-8, IL-1 beta and IL-6. Immigrant cases had a similar gene expression profile to Dutch cases. Twenty-four of the upregulated genes in patients had an increased expression in immigrant controls as well. The fold changes of an additional 14 genes was more than two sd for immigrant controls compared with Dutch controls. Conclusion: Inflammatory genes in monocytes were upregulated both in Dutch and in immigrant patients with first episode psychosis. Immigrant controls showed similar inflammatory gene expression to both patient groups and differed from Dutch controls. The findings suggest that childhood migration and second generation immigrant status may result in a shift of the distribution of immune activation in immigrant populations, which may contribute to the higher rates of psychotic disorders in these groups.