The immune system and schizophrenia: an update for clinicians

Peripheral inflammatory subgroup differences in anterior Default Mode network and multiplex functional network topology are associated with cognition in psychosis

INTRODUCTION

High-inflammation subgroups of patients with psychosis demonstrate cognitive deficits and neuroanatomical alterations. Systemic inflammation assessed using IL-6 and C-reactive protein may alter functional connectivity within and between resting-state networks, but the cognitive and clinical implications of these alterations remain unknown. We aim to determine the relationships of elevated peripheral inflammation subgroups with resting-state functional networks and cognition in psychosis spectrum disorders.

METHODS

Serum and resting-state fMRI were collected from psychosis probands (schizophrenia, schizoaffective, psychotic bipolar disorder) and healthy controls (HC) from the B-SNIP1 (Chicago site) study who were stratified into inflammatory subgroups based on factor and cluster analyses of 13 cytokines (HC Low n = 32, Proband Low n = 65, Proband High n = 29). Nine resting-state networks derived from independent component analysis were used to assess functional and multilayer connectivity. Inter-network connectivity was measured using Fisher z-transformation of correlation coefficients. Network organization was assessed by investigating networks of positive and negative connections separately, as well as investigating multilayer networks using both positive and negative connections. Cognition was assessed using the Brief Assessment of Cognition in Schizophrenia. Linear regressions, Spearman correlations, permutations tests and multiple comparison corrections were used for analyses in R.

RESULTS

Anterior default mode network (DMNa) connectivity was significantly reduced in the Proband High compared to Proband Low (Cohen's d = -0.74, p = 0.002) and HC Low (d = -0.85, p = 0.0008) groups. Inter-network connectivity between the DMNa and the right-frontoparietal networks was lower in Proband High compared to Proband Low (d = -0.66, p = 0.004) group. Compared to Proband Low, the Proband High group had lower negative (d = 0.54, p = 0.021) and positive network (d = 0.49, p = 0.042) clustering coefficient, and lower multiplex network participation coefficient (d = -0.57, p = 0.014). Network findings in high inflammation subgroups correlate with worse verbal fluency, verbal memory, symbol coding, and overall cognition.

CONCLUSION

These results expand on our understanding of the potential effects of peripheral inflammatory signatures and/or subgroups on network dysfunction in psychosis and how they relate to worse cognitive performance. Additionally, the novel multiplex approach taken in this study demonstrated how inflammation may disrupt the brain's ability to maintain healthy co-activation patterns between the resting-state networks while inhibiting certain connections between them.

Protocol for the Psychosis Immune Mechanism Stratified Medicine (PIMS) trial: a randomised double-blind placebo-controlled trial of single-dose tocilizumab in patients with psychosis

INTRODUCTION

Evidence suggests a potentially causal role of interleukin 6 (IL-6), a pleiotropic cytokine that generally promotes inflammation, in the pathogenesis of psychosis. However, no interventional studies in patients with psychosis, stratified using inflammatory markers, have been conducted to assess the therapeutic potential of targeting IL-6 in psychosis and to elucidate potential mechanism of effect. Tocilizumab is a humanised monoclonal antibody targeting the IL-6 receptor to inhibit IL-6 signalling, licensed in the UK for treatment of rheumatoid arthritis. The primary objective of this study is to test whether IL-6 contributes to the pathogenesis of first episode psychosis and to examine potential mechanisms by which IL-6 affects psychotic symptoms. A secondary objective is to examine characteristics of inflammation-associated psychosis.

METHODS AND ANALYSIS

A proof-of-concept study employing a randomised, parallel-group, double-blind, placebo-controlled design testing the effect of IL-6 inhibition on anhedonia in patients with psychosis. Approximately 60 participants with a diagnosis of schizophrenia and related psychotic disorders (ICD-10 codes F20, F22, F25, F28, F29) with evidence of low-grade inflammation (IL-6≥0.7 pg/mL) will receive either one intravenous infusion of tocilizumab (4.0 mg/kg; max 800 mg) or normal saline. Psychiatric measures and blood samples will be collected at baseline, 7, 14 and 28 days post infusion. Cognitive and neuroimaging data will be collected at baseline and 14 days post infusion. In addition, approximately 30 patients with psychosis without evidence of inflammation (IL-6<0.7 pg/mL) and 30 matched healthy controls will be recruited to complete identical baseline assessments to allow for comparison of the characteristic features of inflammation-associated psychosis.

ETHICS AND DISSEMINATION

The study is sponsored by the University of Bristol and has been approved by the Cambridge East Research Ethics Committee (reference: 22/EE/0010; IRAS project ID: 301682). Study findings will be published in peer-review journals. Findings will also be disseminated by scientific presentation and other means.

TRIAL REGISTRATION NUMBER

ISRCTN23256704.

The Effect of Interleukin-2 -330 T/G Polymorphism in People with Schizophrenia Among The Batak and Javanese Ethnic Groups

Background

Schizophrenia is a complex disorder involving multiple genes with mild to moderate effects and non-genetic risk factors such as environmental and psychological influences that alter brain chemistry. Significant reduction in interleukin-2 production by peripheral lymphocytes is an immunological finding replicated in schizophrenia across various countries. Investigations on the interleukin-2 -330 T/G polymorphism in people with schizophrenia (PWS) are still minimal, and the study location involves only a few countries with different results. Therefore, this study aims to examine the effect of interleukin-2 -330 T/G polymorphisms in people with schizophrenia among the Batak and Javanese ethnic groups in Indonesia, particularly in North Sumatra.

Method

This study used purposive non-probability sampling to recruit people with schizophrenia with 120 Batak and 120 Javanese subjects who were hospitalized at Prof. M. Ildrem Mental Hospital, Medan, Indonesia. The interleukin-2 -330 T/G polymorphism was examined by the PCR method.

Result

The results showed that the genotype frequency of the Batak people with schizophrenia is as follows: GG 11.7%, TG 53.3% and TT 35%. Furthermore, the group of Javanese people with schizophrenia is as follows: GG 23.3%, TG 44.2% and TT 32.5%. The OR for the genotypic comparison of GG was found to be 2.154 with 95% CI 0.992-4.678, p=0.053, while that of the TG genotype was 0.892 with 95% CI 0.505-1.574 and p=0.693. The T allele was higher than the G allele in Batak and Javanese ethnic groups, as demonstrated by p=0.713, OR=0.919 with 95% CI 0.641-1.318.

Conclusion

There is no statistically significant difference between the occurrence frequency of alleles. In addition, there is no significant relationship between the GG and the TG genotype of the interleukin-2 - 330T/G polymorphism in people with schizophrenia among the Batak and the Javanese ethnic groups.

Identification of potential biomarkers and their correlation with immune infiltration cells in schizophrenia using combinative bioinformatics strategy

Many studies have identified changes in gene expression in brains of schizophrenia patients and their altered molecular processes, but the findings in different datasets were inconsistent and diverse. Here we performed the most comprehensive analysis of gene expression patterns to explore the underlying mechanisms and the potential biomarkers for early diagnosis in schizophrenia. We focused on 10 gene expression datasets in post-mortem human brain samples of schizophrenia downloaded from gene expression omnibus (GEO) database using the integrated bioinformatics analyses including robust rank aggregation (RRA) algorithm, Weighted gene co-expression network analysis (WGCNA) and CIBERSORT. Machine learning algorithm was used to construct the risk prediction model for early diagnosis of schizophrenia. We identified 15 key genes (SLC1A3, AQP4, GJA1, ALDH1L1, SOX9, SLC4A4, EGR1, NOTCH2, PVALB, ID4, ABCG2, METTL7A, ARC, F3 and EMX2) in schizophrenia by performing multiple bioinformatics analysis algorithms. Moreover, the interesting part of the study is that there is a correlation between the expression of hub genes and the immune infiltrating cells estimated by CIBERSORT. Besides, the risk prediction model was constructed by using both these genes and the immune cells with a high accuracy of 0.83 in the training set, and achieved a high AUC of 0.77 for the test set. Our study identified several potential biomarkers for diagnosis of SCZ based on multiple bioinformatics algorithms, and the constructed risk prediction model using these biomarkers achieved high accuracy. The results provide evidence for an improved understanding of the molecular mechanism of schizophrenia.

Identification of potential blood biomarkers for early diagnosis of schizophrenia through RNA sequencing analysis

Schizophrenia (SCZ) is a highly heritable, polygenic complex mental disorder with imprecise diagnostic boundaries. Finding sensitive and specific novel biomarkers to improve the biological homogeneity of SCZ diagnosis is still one of the research hotspots. To identify the blood specific diagnostic biomarkers of SCZ, we performed RNA sequencing (RNA-seq) on 30 peripheral blood samples from 15 first-episode drug-naïve SCZ patients and 15 healthy controls (CTL). By performing multiple bioinformatics analysis algorithms based on RNA-seq data and microarray datasets, including differential expression genes (DEGs) analysis, WGCNA and CIBERSORT, we first identified 6 specific key genes (TOMM7, SNRPG, KRT1, AQP10, TMEM14B and CLEC12A) in SCZ. Moreover, we found that the proportions of lymphocyte, monocyte and neutrophils were significantly distinct in SCZ patients with CTL samples. Therefore, combining various features including age, sex and the novel blood biomarkers, we constructed the risk prediction model with three classifiers (RF: Random Forest; SVM: support vector machine; DT: decision tree) through repeated k-fold cross validation ensuring better generalizability. Finest result of Area under Receiver Operating Characteristic (AUROC) score of 0.91 was achieved by RF classifier and with a comparable good performance of AUROC 0.77 in external validation dataset. A lower AUROC of 0.63 was demonstrated when it was further applied to a Bipolar disorder (BPD) cohort. In conclusion, the study identified three peripheral core immunocytes and six key genes associated with the occurrence of SCZ, and further studies are required to test and validate these novel biomarkers for early diagnosis and treatment of SCZ.

Multivariate relationships between peripheral inflammatory marker subtypes and cognitive and brain structural measures in psychosis

Elevations in peripheral inflammatory markers have been reported in patients with psychosis. Whether this represents an inflammatory process defined by individual or subgroups of markers is unclear. Further, relationships between peripheral inflammatory marker elevations and brain structure, cognition, and clinical features of psychosis remain unclear. We hypothesized that a pattern of plasma inflammatory markers, and an inflammatory subtype established from this pattern, would be elevated across the psychosis spectrum and associated with cognition and brain structural alterations. Clinically stable psychosis probands (Schizophrenia spectrum, n = 79; Psychotic Bipolar disorder, n = 61) and matched healthy controls (HC, n = 60) were assessed for 15 peripheral inflammatory markers, cortical thickness, subcortical volume, cognition, and symptoms. A combination of unsupervised exploratory factor analysis and hierarchical clustering was used to identify inflammation subtypes. Levels of IL6, TNFα, VEGF, and CRP were significantly higher in psychosis probands compared to HCs, and there were marker-specific differences when comparing diagnostic groups. Individual and/or inflammatory marker patterns were associated with neuroimaging, cognition, and symptom measures. A higher inflammation subgroup was defined by elevations in a group of 7 markers in 36% of Probands and 20% of HCs. Probands in the elevated inflammatory marker group performed significantly worse on cognitive measures of visuo-spatial working memory and response inhibition, displayed elevated hippocampal, amygdala, putamen and thalamus volumes, and evidence of gray matter thickening compared to the proband group with low inflammatory marker levels. These findings specify the nature of peripheral inflammatory marker alterations in psychotic disorders and establish clinical, neurocognitive and neuroanatomic associations with increased inflammatory activation in psychosis. The identification of a specific subgroup of patients with inflammatory alteration provides a potential means for targeting treatment with anti-inflammatory medications.

Neutrophils to lymphocytes ratio and psychosis in 22q11.2 deletion syndrome - Clinical and scientific implications

BACKGROUND

Individuals with 22q11.2 deletion syndrome (22q11.2DS) are at risk for having both psychotic and immune disorders, thus, implying a possible link between the two. The aim of the current study was to evaluate the usefulness of the neutrophiles to leukocytes ratio (NLR), an inflammatory marker, as a bio-marker for overt and prodromal psychotic symptoms in 22q11.2DS.

METHODS

Forty-nine individuals with 22q11.2DS (13 with psychotic disorders and 36 without psychotic disorders) and 30 age- and sex-matched healthy controls underwent psychiatric evaluation using a structured psychiatric interview, the Scale of Prodromal Symptoms (SOPS) and the Global Assessment of Functioning (GAF) scale. Blood samples were collected from all participants on the day of assessment. NLR was calculated, compared among the study groups and correlated with SOPS and GAF scores. The non-psychotic 22q11.2DS group was further divided into high- and low-inflammation groups by NLR values and the analyses were done again.

RESULTS

NLR was higher in the psychotic- and the high-inflammation non-psychotic 22q11.2DS groups compared to the low-inflammation non-psychotic 22q11.2DS group and controls. In the high-inflammation non-psychotic 22q11.2DS group NLR increase was associated with an increase of total negative symptoms scores on SOPS and a decrease in GAF scores.

CONCLUSION

Our results suggest the potential utility of NLR as a bio-marker for psychotic disorders and subthreshold prodromal symptoms in 22q11.2DS. Furthermore, they imply that a disequilibrium between the innate and adaptive arms of the immune system facilitates the progression of psychosis in at risk populations. Further longitudinal studies are warranted to validate our findings, as this was a cross sectional observation.

Cytokines, Oxidative Stress and Cellular Markers of Inflammation in Schizophrenia

In this article, we review current evidence linking immune dysfunction in schizophrenia and related psychotic disorders focusing particularly on circulating cytokines, oxidative stress and cellular markers of inflammation in various stages on illness from drug-naïve first episode psychosis to chronic schizophrenia. Acute psychotic episode is associated with low-grade systemic inflammation in some patients, as reflected by increased concentrations of cytokines and other inflammatory markers in peripheral blood. Evidence from general population-based longitudinal cohort studies reporting an association between elevated inflammatory markers in childhood/adolescence and risk of schizophrenia and related psychosis subsequently in adulthood suggest that inflammation could be a causal risk factor for psychosis rather than simply be a consequence of illness. Mendelian randomization studies also suggest that associations between IL-6, CRP and schizophrenia are likely to be causal. In addition, we discuss evidence for disruptions in oxidative stress markers and CSF cytokine levels in schizophrenia, and potential reasons for reported trans-diagnostic associations for inflammatory cytokines including role of early-life adversity/maltreatment. We argue that low-grade inflammation is a clinically useful feature, because it is associated with poor response to antipsychotic medication in first episode psychosis. We discuss clinical implications for immunological understanding of schizophrenia including scope for clinical trials of anti-inflammatory agents and notable gaps in current knowledge, and offer suggestions for future research.

Immune abnormalities across psychiatric disorders: clinical relevance

It is well established that the immune system can modulate brain functioning and influence behavioural processes. Awareness of communication between the immune and nervous systems has, over the years, progressively heightened interest in the relationship between psychiatric disorders and immune function. By reviewing findings from studies investigating inflammation in the periphery and in the central nervous systems, we summarise here the evidence linking inflammation to the development of depression, schizophrenia and bipolar disorder. We discuss how a pathophysiological role for inflammation has now been recognised across different psychiatric disorders, at least in a significant subpopulation of patients. Finally, we discuss a possible role for these findings in the development of future diagnostic classifications of psychiatric disorders as well as of new treatment strategies.

Interleukin-17 Alteration in First-Episode Psychosis: A Meta-Analysis

Schizophrenia is accompanied with central nervous system and peripheral immune system imbalances. Interleukin-17 (IL-17) is implicated in various immune and inflammatory processes. Aberrant levels of IL-17 have been reported in patients with schizophrenia, whereas the results are not consistent. To clarify the relationship between IL-17 and schizophrenia, we performed a meta-analysis in this study. We carried out a structured literature search in PubMed and Embase database up to April 16, 2017, and retrieved all eligible case-control studies according to the inclusion criteria. Finally, a total of 313 patients with drug-naïve first-episode psychosis and 238 healthy control subjects from 5 studies were included in our meta-analysis. There were no significant differences between first-episode psychosis patients and healthy controls with respect to the levels of IL-17 (p = 0.21), even when we removed 2 studies which were not European samples (p = 0.12). Our findings suggested that IL-17 may not be involved in the pathological mechanism of schizophrenia.

Cytokine function in medication-naive first episode psychosis: a systematic review and meta-analysis

This systematic review sets out to give a comprehensive overview of the cytokine profile at the onset of psychosis un-confounded by medication. We aim to provide insight into the early pathophysiological process of psychosis and areas for future research of potential biomarkers able to chart the extent of illness or effectiveness of treatment. Following PRISMA guidelines, a systematic primary search identified 4638 citations, 4651 studies were retrieved and screened, and 23 studies met the inclusion criteria (published in English before June 2013, patients with neuroleptic naive first episode psychosis, and assessed circulating cytokines). These reported 570 patients, 683 healthy control subjects, and 20 cytokine/cytokine receptors. Papers that contained sufficient stratified data were included in a random-effects pooled effect size meta-analysis. Highly significant effect sizes were found for elevated IL-1β, sIL-2r, IL-6, and TNF-α. Non-significant effect size estimates were obtained for IL-2, IL-4, and IFN-γ. Thus, we found significant elevation in pro-inflammatory cytokine levels in the serum of patients with medication-naive first episode psychosis. This adds to the evidence of a pro-inflammatory immune deregulation in schizophrenia and suggests these cytokines should be the focus for further research in biomarkers of progress and extent of illness. Future studies should focus on the medication-naive group at the early stages of illness with numbers large enough to allow for the control of other potential confounding factors.