Our hypothesis that lifetime psychotic features would be associated with pro-inflammatory monocyte gene expression was not confirmed. In an explorative analysis we found: (i) a possible relationship between pro-inflammatory gene expression and manic symptomatology; (ii) a differential immune activation related to age at onset and duration of illness; and (iii) support for the concept of an immune suppressive action of some of the mood-regulating medications.

Purpose of review Schizophrenia (SCZ) and bipolar disorder are severe mental disorders, both placing a significant burden on individuals' wellbeing and global health generally. The complex interaction of multiple mechanisms, underlying these disorders, still needs further elucidation. Increased activation of components of the immune system may be involved, including alterations in intestinal permeability and gut microbiome. Probiotics, defined as living microorganisms conferring health benefits to the host when administered in adequate amounts, seem to have supportive therapeutic effect in psychiatric disorders. The authors in this review provide an overview of this emerging research field and summarize both the publicated microbiome studies in SCZ and bipolar disorder and the current clinical research using probiotic supplementation in patients diagnosed with these disorders. Recent findingsThe current data indicate that there are differences in the microbiome in SCZ and bipolar disorder patients as compared with healthy controls. Part of these differences may be induced by medication use, others by smoking and other lifestyle factors. Correlations between microbiome quantification and symptom severity have been observed in cross-sectional studies, but unfortunately, no replicated findings so far. Probiotic supplementation was shown not only to alleviate gastrointestinal complaints but also reduce symptom severity, rehospitalization rates and cognitive improvement. Replication of improvement of cognition is needed. SummaryDifferences in microbiome have been shown in both SCZ and bipolar disorder in comparison to healthy controls. Evidence that probiotics can improve psychiatric functioning is still very limited.