Association of IL-17A levels with immuneinflammatory profile and structural MRI data in patients with schizophrenia

IL-17A is a proinflammatory cytokine involved in pathogenesis of some neuroinflammatory diseases of the brain. However, its role in schizophrenia is poorly understood. Currently, noninvasive neuroimaging techniques are widely used to assess abnormalities in brain morphology and interactions of neuronal networks in schizophrenia. The aim of this work was to study associations between IL-17A level and brain morphometric parameters in schizophrenia, in order to clarify immune factors of pathogenesis and search for biomarkers of unfavorable disease course. 45 patients with schizophrenia and 30 healthy volunteers were included into the study. The levels of cytokines (IL-5, IL-6, IL-8, IL-10, IL-17A) and inflammatory markers were determined by ELISA or multiplex analysis. MRI scans were performed with a Siemens Magnetom Verio 3T MRI scanner. We used Kruskal–Wallis test to assess significant differences in immunological parameters followed by Mann–Whitney paired comparison; Student test to assess the significance of differences in morphometric parameters of the brain; Fisher exact test to assess the differences in discrete variables, with the differences considered statistically significant at p < 0.05. IL-17A levels were found to be increased in schizophrenia. Its elevated content was associated with increased levels of C-reactive protein, IL-5, IL-6, IL-8, IL-10, and the presence of morphometric changes of frontal and temporal cortex in the patients. So far, the relationships between IL-17A levels, immunoinflammatory parameters and structural brain changes have not been studied in schizophrenia. In the present work, we found an association of elevated IL-17A levels with decreased cortical thickness in several brain regions, systemic inflammation and activation of Th2-link of adaptive immunity in the patients with schizophrenia. According to the literature, a number of brain areas, where cortical thickness was associated with IL-17A levels may be relevant to pathogenesis of the disease and, in particular, to the development of negative symptoms, including impoverishment of interests, speech, and emotions. The results are important for understanding the role of immune disorders in pathogenesis of schizophrenia, including structural changes of the brain, and suggest that IL-17A may be a biomarker of these disorders. Confirmation of associations between structural neuroimaging findings, laboratory markers of inflammation and immune disorders may provide the basis for new multidisciplinary approaches to the diagnosis and prognosis of schizophrenia.