Variation in the major histocompatibility complex [MHC] gene family in schizophrenia: associations and functional implications

Narcolepsy and psychiatric disorders: A bidirectional Mendelian randomization study

Since the introduction of the concept of narcolepsy, there has been a proliferation of discussions about its association with psychiatry. To elucidate the causal role of narcolepsy in the three psychiatric disorders [i.e., schizophrenia (SCZ), major depressive disorder (MDD), and attention-deficit hyperactivity disorder (ADHD)], we applied a bidirectional Mendelian randomization study using two stages (discovery stage and validation stage) and data from three different genome-wide association studies of narcolepsy. The estimates from different stages were combined using fixed-effects meta-analysis. Our findings suggest that narcolepsy is associated with an increased risk of SCZ. Conversely, MDD may be causally related to narcolepsy. A causal relationship between narcolepsy and ADHD was excluded.

Peripheral cytokine levels across psychiatric disorders: A systematic review and network meta-analysis

Immune dysregulated cytokine production is involved in mental diseases. However, the results are inconsistent and the pattern of cytokine alterations has not been compared across disorders. We performed a network impact analysis of cytokine levels for different psychiatric disorders including schizophrenia, major depressive disorder, bipolar disorder, panic disorder, post-traumatic stress disorder and obsessive compressive disorder to evaluate their clinical impact across conditions. Studies were identified by searching the electronic databases up to 31/05/2022. A total of eight cytokines, together with (high-sensitivity) C-reactive proteins (hsCRP/CRP) were included in the network meta-analysis. The levels of proinflammatory cytokines, hsCRP/CRP and interleukin 6 (IL-6) were significantly increased in patients with psychiatric disorders when compared to controls. IL-6 showed no significant difference among comparisons between disorders according to the network meta-analysis. Interleukin 10 (IL-10) is significantly increased in patients with bipolar disorder compared to major depressive disorder. Further, the level of interleukin-1 beta (IL-1β) was significantly increased in major depressive disorder as compared to bipolar disorder. The level of interleukin 8 (IL-8) varied among these psychiatric disorders based on the network meta-analysis result. Overall, abnormal cytokine levels were found in psychiatric disorders, and some of the cytokines displayed differential characteristics in these disorders, especially IL-8, pointing to a role as potential biomarkers for general and differential diagnosis.

Variants of Th17 pathway-related genes influence brain morphometric changes and the risk of schizophrenia through epistatic interactions

OBJECTIVE

T helper 17 (Th17) pathway has been reported to be abnormal in schizophrenia; however, it is not known whether variation within genes of this pathway has any impact on schizophrenia. Herein, the impact of genetic variations and gene-gene interactions of Th17 pathway-related genes on the risk, psychopathology, and brain volume was examined in schizophrenia patients.

METHODS

Functional polymorphisms within interleukin 6 ( IL6 )(rs1800795 and rs1800797), IL10 (rs1800872 and rs1800896), IL17A (rs2275913 and rs8193036), IL22 (rs2227484 and rs2227485), IL23R (rs1884444), and IL27 (rs153109 and rs181206) genes were studied in 224 schizophrenia patients and 226 healthy controls. These variants were correlated with the brain morphometry, analyzed using MRI in a subset of patients ( n = 117) and controls ( n = 137).

RESULTS

Patients carrying CC genotype of rs2227484 of IL22 gene had significantly higher apathy total score [ F (1,183) = 5.60; P = 0.019; partial ɳ 2 = 0.030]. Significant epistatic interactions between IL6 (rs1800797) and IL17A (rs2275913) genes were observed in schizophrenia patients. GG genotype of rs2275913 of IL17A gene was associated with reduced right middle occipital gyrus volume in schizophrenia patients ( T = 4.56; P < 0.001).

CONCLUSION

Interactions between genes of Th17 pathway impact the risk for schizophrenia. The variants of Th17 pathway-related genes seem to have a determining effect on psychopathology and brain morphometric changes in schizophrenia.

Changes in peripheral blood compounds following psychopharmacological treatment in drug-naïve first-episode patients with either schizophrenia or major depressive disorder: a meta-analysis

BACKGROUND

This meta-analysis on peripheral blood compounds in drug-naïve first-episode patients with either schizophrenia or major depressive disorder (MDD) examined which compounds change following psychopharmacological treatment.

METHODS

The Embase, PubMed and PsycINFO databases were systematically searched for longitudinal studies reporting measurements of blood compounds in drug-naïve first-episode schizophrenia or MDD.

RESULTS

For this random-effects meta-analysis, we retrieved a total of 31 studies comprising 1818 schizophrenia patients, and 14 studies comprising 469 MDD patients. Brain-derived neurotrophic factor (BDNF) increased following treatment in schizophrenia (Hedges' g (g): 0.55; 95% confidence interval (CI) 0.39-0.70; p < 0.001) and MDD (g: 0.51; CI 0.06-0.96; p = 0.027). Interleukin (IL)-6 levels decreased in schizophrenia (g: -0.48; CI -0.85 to -0.11; p = 0.011), and for MDD a trend of decreased IL-6 levels was observed (g: -0.39; CI -0.87 to 0.09; p = 0.115). Tumor necrosis factor alpha (TNFα) also decreased in schizophrenia (g: -0.34; CI -0.68 to -0.01; p = 0.047) and in MDD (g: -1.02; CI -1.79 to -0.25; p = 0.009). Fasting glucose levels increased only in schizophrenia (g: 0.26; CI 0.07-0.44; p = 0.007), but not in MDD. No changes were found for C-reactive protein, IL-1β, IL-2 and IL-4.

CONCLUSIONS

Psychopharmacological treatment has modulating effects on BDNF and TNFα in drug-naïve first-episode patients with either schizophrenia or MDD. These findings support efforts for further research into transdiagnostic preventive strategies and augmentation therapy for those with immune dysfunctions.

Role of Polyinosinic:Polycytidylic Acid-Induced Maternal Immune Activation and Subsequent Immune Challenge in the Behaviour and Microglial Cell Trajectory in Adult Offspring: A Study of the Neurodevelopmental Model of Schizophrenia

Multiple lines of evidence support the pathogenic role of maternal immune activation (MIA) in the occurrence of the schizophrenia-like disturbances in offspring. While in the brain the homeostatic role of neuron-microglia protein systems is well documented, the participation of the CX3CL1-CX3CR1 and CD200-CD200R dyads in the adverse impact of MIA often goes under-recognized. Therefore, in the present study, we examined the effect of MIA induced by polyinosinic:polycytidylic acid (Poly I:C) on the CX3CL1-CX3CR1 and CD200-CD200R axes, microglial trajectory (MhcII, Cd40, iNos, Il-1β, Tnf-α, Il-6, Arg1, Igf-1, Tgf-β and Il-4), and schizophrenia-like behaviour in adult male offspring of Sprague-Dawley rats. Additionally, according to the “two-hit” hypothesis of schizophrenia, we evaluated the influence of acute challenge with Poly I:C in adult prenatally MIA-exposed animals on the above parameters. In the present study, MIA evoked by Poly I:C injection in the late period of gestation led to the appearance of schizophrenia-like disturbances in adult offspring. Our results revealed the deficits manifested as a diminished number of aggressive interactions, presence of depressive-like episodes, and increase of exploratory activity, as well as a dichotomy in the sensorimotor gating in the prepulse inhibition (PPI) test expressed as two behavioural phenotypes (MIA_PPI-low and MIA_PPI-high). Furthermore, in the offspring rats subjected to a prenatal challenge (i.e., MIA) we noticed the lack of modulation of behavioural changes after the additional acute immune stimulus (Poly I:C) in adulthood. The important finding reported in this article is that MIA affects the expression and levels of the neuron-microglia proteins in the frontal cortex and hippocampus of adult offspring. We found that the changes in the CX3CL1-CX3CR1 axis could affect microglial trajectory, including decreased hippocampal mRNA level of MhcII and elevated cortical expression of Igf-1 in the MIA_PPI-high animals and/or could cause the up-regulation of an inflammatory response (Il-6, Tnf-α, iNos) after the “second hit” in both examined brain regions and, at least in part, might differentiate behavioural disturbances in adult offspring. Consequently, the future effort to identify the biological background of these interactions in the Poly I:C-induced MIA model in Sprague-Dawley rats is desirable to unequivocally clarify this issue.

Altered peripheral blood compounds in drug-naïve first-episode patients with either schizophrenia or major depressive disorder: a meta-analysis

IMPORTANCE

Schizophrenia and major depressive disorder (MDD) are associated with increased risks of immunologic disease and metabolic syndrome. It is unclear to what extent growth, immune or glucose dysregulations are similarly present in these disorders without the influence of treatment or chronicity.

OBJECTIVE

To conduct a meta-analysis investigating whether there are altered peripheral growth, immune or glucose metabolism compounds in drug-naïve first-episode patients with schizophrenia or MDD compared with controls.

DATA SOURCES AND STUDY SELECTION

Case-control studies reporting compound measures in drug-naïve first-episode patients with schizophrenia or MDD compared with controls in the Embase, PubMed and PsycINFO databases.

DATA EXTRACTION AND SYNTHESIS

Two independent authors extracted data for a random-effects meta-analysis.

MAIN OUTCOMES AND MEASURES

Peripheral growth, immune or glucose metabolism compounds in schizophrenia or MDD compared with controls. Standardized mean differences were quantified with Hedges' g (g).

RESULTS

74 studies were retrieved comprising 3453 drug-naïve first-episode schizophrenia patients and 4152 controls, and 29 studies were retrieved comprising 1095 drug-naïve first-episode MDD patients and 1399 controls. Growth factors: brain-derived neurotrophic factor (BDNF) (g = -0.77, P < .001) and nerve growth factor (NGF) (g = -2.51, P = .03) were decreased in schizophrenia. For MDD, we observed a trend toward decreased BDNF (g = -0.47, P = .19) and NGF (g = -0.33, P = .08) levels, and elevated vascular endothelial growth factor levels (g = 0.40, P = .03). Immune factors: interleukin (IL)-6 (g = 0.95, P < .001), IL-8 (g = 0.59, P = .001) and tumor necrosis factor alpha (TNFα) (g = 0.48, P = .002) were elevated in schizophrenia. For C-reactive protein (CRP) (g = 0.57, P = .09), IL-4 (g = 0.44, P = .10) and interferon gamma (g = 0.33, P = .11) we observed a trend toward elevated levels in schizophrenia. In MDD, IL-6 (g = 0.62, P = .007), TNFα (g = 1.21, P < .001), CRP (g = 0.53, P < .001), IL-1β (g = 1.52, P = .009) and IL-2 (g = 4.41, P = .04) were elevated, whereas IL-8 (g = -0.84, P = .01) was decreased. The fasting glucose metabolism factors glucose (g = 0.24, P = .003) and insulin (g = 0.38, P = .003) were elevated in schizophrenia.

CONCLUSIONS AND RELEVANCE

Both schizophrenia and MDD show alterations in growth and immune factors from disease onset. An altered glucose metabolism seems to be present from onset in schizophrenia. These findings support efforts for further research into transdiagnostic preventive strategies and augmentation therapy for those with immune or metabolic dysfunctions.

Integrating genome-wide association study and methylation functional annotation data identified candidate genes and pathways for schizophrenia

BACKGROUND

Schizophrenia (SCZ) is a severe mental disorder. Both environmental and genetic factors contribute to the development of SCZ. The estimated heritability of SCZ is about 80%. Previous genetic studies of SCZ mainly focused on the genetic variations associated the risk of SCZ. Limited efforts are paid to explore the roles and biological mechanism of nuclear acid methylation implicated in the pathogenesis of SCZ.

METHODS

A two-stage integrative analysis of SCZ GWAS and nuclear acid methylation functional annotation data (including meQTLs and m6A) was performed in this study. First, the discovery GWAS of SCZ was aligned with genomic meQTLs and m6A annotation data to identify the candidate genes associated with SCZ. Second, another independent replication GWAS dataset of SCZ was applied to validate the discovery results. Furthermore, the functional relevance of identified candidate genes with SCZ were validated by the mRNA expression profiling of SCZ brain tissues. Gene ontology (GO) and pathway enrichment analysis of identified candidate genes was performed by the DAVID tool.

RESULTS

The two-stage integrative analysis detected 106 meQTLs related candidate genes for SCZ. After comparing with the differentially expressed genes in SCZ brain tissues, 49 overlapped genes were identified for meQTLs, such as ZSCAN12, BTN3A2 and HLA-DQA1. Besides, for meQTLs, 29 SCZ associated pathways and 56 SCZ associated GO terms were detected, such as cell adhesion molecules and asthma. For m6A, 25 candidate genes were detected by the two-stage integrative analysis for SCZ, such as ZSCAN12, HLA-DQA1 and SNX19. Furthermore, 17 of the 25 genes were detected in the mRNA expression profiling of SCZ brain tissues.

CONCLUSION

This study identified multiple SCZ associated genes and pathways, supporting the implication of nuclear acid methylation in the pathogenesis of SCZ.

Comorbidity of Narcolepsy and Psychotic Disorders: A Nationwide Population-Based Study in Taiwan

BACKGROUND

Narcolepsy is a chronic sleep disorder that is likely to have neuropsychiatric comorbidities. Psychotic disorders are characterized by delusion, hallucination, and reality impairments. This study investigates the relationship between narcolepsy and psychotic disorders.

DESIGN AND METHODS

This study involves patients who were diagnosed with narcolepsy between January 2002 and December 2011 (n = 258) and age- and gender-matched controls (n = 2580) from Taiwan's National Health Insurance database. Both the patients and the controls were monitored from January 1, 2002 to December 31, 2011 to identify any occurrence of a psychotic disorder. Drugs that have been approved for treating narcolepsy: immediate-release methylphenidate (IR-MPH), osmotic controlled-release formulations of methylphenidate (OROS-MPH), and modafinil, were analyzed. A multivariate logistic regression model was used to evaluate the potential comorbidity of narcolepsy with psychotic disorders.

RESULTS

During the study period, 8.1% of the narcoleptic patients exhibited comorbidity with a psychotic disorder, whereas only 1.5% of the control subjects (1.5%) had psychotic disorders (aOR, 4.07; 95% CI, 2.21-7.47). Of the narcolepsy patients, 41.5, 5.4, and 13.2% were treated with MPH-IR, MPH-OROS, and modafinil, accordingly. Pharmacotherapy for narcolepsy did not significantly affect the risk of exhibiting a psychotic disorder.

CONCLUSIONS

This nationwide study revealed that narcolepsy and psychotic disorders commonly co-occur. Pharmacotherapy for narcolepsy was not associated with the risk of psychotic disorders. Our findings serve as a reminder that clinicians must consider the comorbidity of narcolepsy and psychosis.

An update on the efficacy of anti-inflammatory agents for patients with schizophrenia: a meta-analysis

BACKGROUND

Accumulating evidence shows that a propensity towards a pro-inflammatory status in the brain plays an important role in schizophrenia. Anti-inflammatory drugs might compensate this propensity. This study provides an update regarding the efficacy of agents with some anti-inflammatory actions for schizophrenia symptoms tested in randomized controlled trials (RCTs).

METHODS

PubMed, Embase, the National Institutes of Health website (http://www.clinicaltrials.gov), and the Cochrane Database of Systematic Reviews were systematically searched for RCTs that investigated clinical outcomes.

RESULTS

Our search yielded 56 studies that provided information on the efficacy of the following components on symptom severity: aspirin, bexarotene, celecoxib, davunetide, dextromethorphan, estrogens, fatty acids, melatonin, minocycline, N-acetylcysteine (NAC), pioglitazone, piracetam, pregnenolone, statins, varenicline, and withania somnifera extract. The results of aspirin [mean weighted effect size (ES): 0.30; n = 270; 95% CI (CI) 0.06-0.54], estrogens (ES: 0.78; n = 723; CI 0.36-1.19), minocycline (ES: 0.40; n = 946; CI 0.11-0.68), and NAC (ES: 1.00; n = 442; CI 0.60-1.41) were significant in meta-analysis of at least two studies. Subgroup analysis yielded larger positive effects for first-episode psychosis (FEP) or early-phase schizophrenia studies. Bexarotene, celecoxib, davunetide, dextromethorphan, fatty acids, pregnenolone, statins, and varenicline showed no significant effect.

CONCLUSIONS

Some, but not all agents with anti-inflammatory properties showed efficacy. Effective agents were aspirin, estrogens, minocycline, and NAC. We observed greater beneficial results on symptom severity in FEP or early-phase schizophrenia.

Reduced cortical thickness related to single nucleotide polymorphisms in the major histocompatibility complex region in antipsychotic-naive schizophrenia

The aim of this study was to explore the relationships between changes in cortical thickness and single nucleotide polymorphisms (SNPs) in the major histocompatibility complex (MHC) region in a group of antipsychotic-naive schizophrenia (AN-SCZ) patients. Methods Twenty-five AN-SCZ patients and 51 healthy controls (HCs) participated in this study. General linear models were used to identify associations between the average cortical thicknesses of each brain region (N = 68) and each of the 11 SNPs in the MHC region in the AN-SCZ patients and HCs. Next, we performed independent-sample t tests to investigate whether cortical thickness was significantly lower in the AN-SCZ patients than in HCs in the brain regions that were significantly associated with the SNPs. Finally, we examined the correlations between clinical symptoms and cortical thickness in the above brain areas in the whole AN-SCZ group using Pearson correlation tests. Results Seven of the 11 SNPs within the MHC region were significantly associated with cortical thickness only in the AN-SCZ patients; these included rs1635, rs1736913, rs2021722, rs204999, rs2523722, rs3131296, and rs9272105. The AN-SCZ patients had significantly thinner cortical thicknesses in the above brain regions, especially the prefrontal cortex. Furthermore, the left entorhinal region was negatively correlated with Positive and Negative Symptom Scale (PANSS) activation scores in the AN-SCZ group (r = -0.601, p = 0.03). Conclusions This study provides evidence demonstrating the potential effects of MHC risk variants in cortical thickness deficits in AN-SCZ. These data also support the notion that the immune system plays critical roles in the pathology of schizophrenia, which is mediated via the modulation of the development of cerebral cortical structures.

Association Studies of HSPA1A and HSPA1L Gene Polymorphisms With Schizophrenia

BACKGROUND

Schizophrenia is a severe psychiatric disorder with a strong genetic component. The HSP70 chaperones are particularly interesting in terms of schizophrenia, especially with regard to neurodevelopmental hypothesis, because they are critical regulators in normal neural physiological function as well as in cell stress responses.

AIM OF THE STUDY

The present study aimed to determine whether genetic variants in the HSPA1A (rs1008438, rs562047) and HSPA1L (rs2075800) genes are associated with the risk of paranoid schizophrenia and the clinical presentation of the disease.

METHODS

A total of 1080 unrelated Polish subjects of Caucasian origin (401 schizophrenia cases and 679 healthy controls) were recruited. Three single nucleotide polymorphisms (SNP) were genotyped using PCR-RFLP (rs562047) or TaqMan (rs1008438, rs2075800) assays. All analyses were conducted for the full sample and within subgroups stratified by gender.

RESULTS

There were no statistically significant differences in genotype or allele distributions of all polymorphisms tested between the schizophrenia and control groups. We also failed to find any schizophrenia predisposing haplotype in the whole group. A sex-stratified analysis revealed haplotypic association with paranoid schizophrenia in men, albeit the risk effect was contributed only by a rare haplotypes. More importantly, rs562047 variant was significantly associated with PANSS total and PANSS negative scores in schizophrenia.

CONCLUSIONS

Our results support previously reported associations between HSPA1A and HSPA1B SNPs and schizophrenia symptomatology. Further population-based prospective studies with larger sample sizes from different ethnic groups should be performed to clarify the role of different HSP70 genes in the pathogenesis of schizophrenia.

Expression of TCN1 in Blood is Negatively Associated with Verbal Declarative Memory Performance

Memory is indispensable for normal cognitive functioning, and the ability to store and retrieve information is central to mental health and disease. The molecular mechanisms underlying complex memory functions are largely unknown, but multiple genome-wide association studies suggest that gene regulation may play a role in memory dysfunction. We performed a global gene expression analysis using a large and balanced case-control sample (n = 754) consisting of healthy controls and schizophrenia and bipolar disorder patients. Our aim was to discover genes that are differentially expressed in relation to memory performance. Gene expression in blood was measured using Illumina HumanHT-12 v4 Expression BeadChip and memory performance was assessed with the updated California Verbal Learning Test (CVLT-II). We found that elevated expression of the vitamin B12-related gene TCN1 (haptocorrin) was significantly associated with poorer memory performance after correcting for multiple testing (β = −1.50, p = 3.75e-08). This finding was validated by quantitative real-time PCR and followed up with additional analyses adjusting for confounding variables. We also attempted to replicate the finding in an independent case-control sample (n = 578). The relationship between TCN1 expression and memory impairment was comparable to that of important determinants of memory function such as age and sex, suggesting that TCN1 could be a clinically relevant marker of memory performance. Thus, we identify TCN1 as a novel genetic finding associated with poor memory function. This finding may have important implications for the diagnosis and treatment of vitamin B12-related conditions.

The immunogenetics of neurological disease

Genes encoding antigen-presenting molecules within the human major histocompatibility complex (MHC) account for the highest component of genetic risk for many neurological diseases, such as multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. Myriad genetic, immunological and environmental factors may contribute to an individual's susceptibility to neurological disease. Here, we review and discuss the decades long research on the influence of genetic variation at the MHC locus and the role of immunogenetic killer cell immunoglobulin-like receptor (KIR) loci in neurological diseases, including multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. The findings of immunogenetic association studies are consistent with a polygenic model of inheritance in the heterogeneous and multifactorial nature of complex traits in various neurological diseases. Future investigation is highly recommended to evaluate both coding and non-coding variation in immunogenetic loci using high-throughput high-resolution next-generation sequencing technologies in diverse ethnic groups to fully appreciate their role in neurological diseases.

The Major Histocompatibility Complex (MHC) in Schizophrenia: A Review

Epidemiological studies and mouse models suggest that maternal immune activation, induced clinically through prenatal exposure to one of several infectious diseases, is a risk factor in the development of schizophrenia. This is supported by the strong genetic association established by genome wide association studies (GWAS) between the human leukocyte antigen (HLA) locus and schizophrenia. HLA proteins (also known in mice as the major histocompatibility complex; MHC) are mediators of the T-lymphocyte responses, and genetic variability is well-established as a risk factor for autoimmune diseases and susceptibility to infectious diseases. Taken together, the findings strongly suggest that schizophrenia risk in a subgroup of patients is caused by an infectious disease, and/or an autoimmune phenomenon. However, this view may be overly simplistic. First, MHC proteins have a non-immune effect on synaptogenesis by modulating synaptic pruning by microglia and other mechanisms, suggesting that genetic variability could be compromising this physiological process. Second, some GWAS signals in the HLA locus map near non-HLA genes, such as the histone gene cluster. On the other hand, recent GWAS data show association signals near B-lymphocyte enhancers, which lend support for an infectious disease etiology. Thus, although the genetic findings implicating the HLA locus are very robust, how genetic variability in this region leads to schizophrenia remains to be elucidated.

Genome-Wide Association Studies Suggest Limited Immune Gene Enrichment in Schizophrenia Compared to 5 Autoimmune Diseases

There has been intense debate over the immunological basis of schizophrenia, and the potential utility of adjunct immunotherapies. The major histocompatibility complex is consistently the most powerful region of association in genome-wide association studies (GWASs) of schizophrenia and has been interpreted as strong genetic evidence supporting the immune hypothesis. However, global pathway analyses provide inconsistent evidence of immune involvement in schizophrenia, and it remains unclear whether genetic data support an immune etiology per se. Here we empirically test the hypothesis that variation in immune genes contributes to schizophrenia. We show that there is no enrichment of immune loci outside of the MHC region in the largest genetic study of schizophrenia conducted to date, in contrast to 5 diseases of known immune origin. Among 108 regions of the genome previously associated with schizophrenia, we identify 6 immune candidates (DPP4, HSPD1, EGR1, CLU, ESAM, NFATC3) encoding proteins with alternative, nonimmune roles in the brain. While our findings do not refute evidence that has accumulated in support of the immune hypothesis, they suggest that genetically mediated alterations in immune function may not play a major role in schizophrenia susceptibility. Instead, there may be a role for pleiotropic effects of a small number of immune genes that also regulate brain development and plasticity. Whether immune alterations drive schizophrenia progression is an important question to be addressed by future research, especially in light of the growing interest in applying immunotherapies in schizophrenia.

The impact of HLA-G 3' UTR variants and sHLA-G on risk and clinical correlates of schizophrenia

The Major Histocompatibility Complex (MHC)/Human Leukocyte Antigen (HLA) is known to influence the pathogenesis of several complex human diseases resulting from gene-environmental interactions. Recently, it has emerged as one of the risk determinants of schizophrenia. The HLA-G protein (a non-classical MHC class I molecule), encoded by the HLA-G gene, is shown to play important role in embryonic development. Importantly, its genetic variations and aberrant expression have been implicated in pregnancy complications like preeclampsia, inflammation, and autoimmunity. Converging evidence implicates these phenomena as risk mechanisms of schizophrenia. However, the functional implications of HLA-G in schizophrenia are yet to be empirically examined. The impact of two functional polymorphisms [14bp Insertion/Deletion (INDEL) and +3187 A>G] and soluble HLA-G (sHLA-G) levels on schizophrenia risk was evaluated. In this exploratory study, the Ins/Ins genotype of 14bp INDEL was found to confer a strong risk for schizophrenia. Further, low levels of sHLA-G were shown to have a significant impact on Clinical Global Impression (CGI) severity in people with schizophrenia.

Leukocyte Ig-Like Receptors - A Model for MHC Class I Disease Associations

MHC class I (MHC-I) polymorphisms are associated with the outcome of some viral infections and autoimmune diseases. MHC-I proteins present antigenic peptides and are recognized by receptors on natural killer cells and cytotoxic T lymphocytes, thus enabling the immune system to detect self-antigens and eliminate targets lacking self or expressing foreign antigens. Recognition of MHC-I, however, extends beyond receptors on cytotoxic leukocytes. Members of the leukocyte Ig-like receptor (LILR) family are expressed on monocytic cells and can recognize both classical and non-classical MHC-I alleles. Despite their relatively broad specificity when compared to the T cell receptor or killer Ig-like receptors, variations in the strength of LILR binding between different MHC-I alleles have recently been shown to correlate with control of HIV infection. We suggest that LILR recognition may mediate MHC-I disease association in a manner that does not depend on a binary discrimination of self/non-self by cytotoxic cells. Instead, the effects of LILR activity following engagement by MHC-I may represent a “degrees of self” model, whereby strength of binding to different alleles determines the degree of influence exerted by these receptors on immune cell functions. LILRs are expressed by myelomonocytic cells and lymphocytes, extending their influence across antigen-presenting cell subsets including dendritic cells, macrophages, and B cells. They have been identified as important players in the response to infection, inflammatory diseases, and cancer, with recent literature to indicate that MHC-I recognition by these receptors and consequent allelic effects could extend an influence beyond the immune system.

Absence of NMDA receptor antibodies in the rare association between Type 1 Narcolepsy and Psychosis

Frequency and mechanisms underlying the association between narcolepsy type 1 (NT1) and psychosis remain unclear with potential role for a common immune pathway. We estimated the frequency of psychosis and its characteristics in NT1 at two European sleep centers (France, n = 381; Spain, n = 161) and measured IgG autoantibodies that recognize the GluN1 subunit of the NMDAR in 9 patients with NT1 with psychosis, and 25 NT1 patients without psychosis. Ten NT1 patients (6 in France, 4 in Spain) were diagnosed with comorbid psychosis, a frequency of 1.8%. One patient reported psychotic symptoms few months before narcolepsy onset, two patients few months after onset, and one patient one year after onset but after modafinil introduction. The six remaining patients reported long delays between NT1 and psychosis onset. Half the patients, mostly male adults, reported onset or worsening of psychotic symptoms after medication. We found no IgG antibodies to NR1/NR2B heteromers of the NMDARs in patients with NT1 with or without psychosis. To conclude, psychosis is rare in NT1, with limited evidence for a key impact of stimulants, and no association with anti-NMDAR antibodies. However, dramatic NT1 and schizophrenia exists especially in early onset NT1, which may lead to inappropriate diagnosis and management.

Altered neural signaling and immune pathways in peripheral blood mononuclear cells of schizophrenia patients with cognitive impairment: A transcriptome analysis

Cognitive deficits are a core feature of schizophrenia and contribute significantly to functional disability. We investigated the molecular pathways associated with schizophrenia (SZ; n=47) cases representing both 'cognitive deficit' (CD; n=22) and 'cognitively spared' (CS; n=25) subtypes of schizophrenia (based on latent class analysis of 9 cognitive performance indicators), compared with 49 healthy controls displaying 'normal' cognition. This was accomplished using gene-set analysis of transcriptome data derived from peripheral blood mononuclear cells (PBMCs). We detected 27 significantly altered pathways (19 pathways up-regulated and 8 down-regulated) in the combined SZ group and a further 6 pathways up-regulated in the CS group and 5 altered pathways (4 down-regulated and 1 up-regulated) in the CD group. The transcriptome profiling in SZ and cognitive subtypes were characterized by the up-regulated pathways involved in immune dysfunction (e.g., antigen presentation in SZ), energy metabolism (e.g., oxidative phosphorylation), and down-regulation of the pathways involved in neuronal signaling (e.g., WNT in SZ/CD and ERBB in SZ). When we looked for pathways that differentiated the two cognitive subtypes we found that the WNT signaling was significantly down-regulated (FDR<0.05) in the CD group in accordance with the combined SZ cohort, whereas it was unaffected in the CS group. This suggested suppression of WNT signaling was a defining feature of cognitive decline in schizophrenia. The WNT pathway plays a role in both the development/function of the central nervous system and peripheral tissues, therefore its alteration in PBMCs may be indicative of an important genomic axis relevant to cognition in the neuropathology of schizophrenia.

Omics-Based Biomarkers: Application of Metabolomics in Neuropsychiatric Disorders

One of the major concerns of modern society is to identify putative biomarkers that serve as a valuable early diagnostic tool to identify a subset of patients with increased risk to develop neuropsychiatric disorders. Biomarker identification in neuropsychiatric disorders is proposed to offer a number of important benefits to patient well-being, including prediction of forthcoming disease, diagnostic precision, and a level of disease description that would guide treatment choice. Nowadays, the metabolomics approach has unlocked new possibilities in diagnostics of devastating disorders like neuropsychiatric disorders. Metabolomics-based technologies have the potential to map early biochemical changes in disease and hence provide an opportunity to develop predictive biomarkers that can be used as indicators of pathological abnormalities prior to development of clinical symptoms of neuropsychiatric disorders. This review highlights different -omics strategies for biomarker discovery in neuropsychiatric disorders. We also highlight initial outcomes from metabolomics studies in psychiatric disorders such as schizophrenia, bipolar disorder, and addictive disorders. This review will also present issues and challenges regarding the implementation of the metabolomics approach as a routine diagnostic tool in the clinical laboratory in context with neuropsychiatric disorders.

Genes involved in pruning and inflammation are enriched in a large mega-sample of patients affected by Schizophrenia and Bipolar Disorder and controls

A molecular pathway analysis has been performed in order to complement previous genetic investigations on Schizophrenia. 4486 Schizophrenic patients and 4477 controls served as the investigation sample. 3521 Bipolar patients and 3195 controls served as replication sample. A molecular pathway associated with the neuronal pruning activity was found to be enriched in subjects with Schizophrenia compared to controls. HLA-C and HLA-DRA had more SNPs associated with both Schizophrenia and Bipolar Disorder than expected by chance.

Adaptive Immunity in Schizophrenia: Functional Implications of T Cells in the Etiology, Course and Treatment

Schizophrenia is a severe and highly complex neurodevelopmental disorder with an unknown etiopathology. Recently, immunopathogenesis has emerged as one of the most compelling etiological models of schizophrenia. Over the past few years considerable research has been devoted to the role of innate immune responses in schizophrenia. The findings of such studies have helped to conceptualize schizophrenia as a chronic low-grade inflammatory disorder. Although the contribution of adaptive immune responses has also been emphasized, however, the precise role of T cells in the underlying neurobiological pathways of schizophrenia is yet to be ascertained comprehensively. T cells have the ability to infiltrate brain and mediate neuro-immune cross-talk. Conversely, the central nervous system and the neurotransmitters are capable of regulating the immune system. Neurotransmitter like dopamine, implicated widely in schizophrenia risk and progression can modulate the proliferation, trafficking and functions of T cells. Within brain, T cells activate microglia, induce production of pro-inflammatory cytokines as well as reactive oxygen species and subsequently lead to neuroinflammation. Importantly, such processes contribute to neuronal injury/death and are gradually being implicated as mediators of neuroprogressive changes in schizophrenia. Antipsychotic drugs, commonly used to treat schizophrenia are also known to affect adaptive immune system; interfere with the differentiation and functions of T cells. This understanding suggests a pivotal role of T cells in the etiology, course and treatment of schizophrenia and forms the basis of this review.

DNA methylation differences in monozygotic twin pairs discordant for schizophrenia identifies psychosis related genes and networks

Background

Despite their singular origin, monozygotic twin pairs often display discordance for complex disorders including schizophrenia. It is a common (1%) and often familial disease with a discordance rate of ~50% in monozygotic twins. This high discordance is often explained by the role of yet unknown environmental, random, and epigenetic factors. The involvement of DNA methylation in this disease appears logical, but remains to be established.

Methods

We have used blood DNA from two pairs of monozygotic twins discordant for schizophrenia and their parents in order to assess genome-wide methylation using a NimbleGen Methylation Promoter Microarray.

Results

The genome-wide results show that differentially methylated regions (DMRs) exist between members representing discordant monozygotic twins. Some DMRs are shared with parent(s) and others appear to be de novo. We found twenty-seven genes affected by DMR changes that were shared in the affected member of two discordant monozygotic pairs from unrelated families. Interestingly, the genes affected by pair specific DMRs share specific networks. Specifically, this study has identified two networks; “cell death and survival” and a “cellular movement and immune cell trafficking”. These two networks and the genes affected have been previously implicated in the aetiology of schizophrenia.

Conclusions

The results are compatible with the suggestion that DNA methylation may contribute to the discordance of monozygotic twins for schizophrenia. Also, this may be accomplished by the direct effect of gene specific methylation changes on specific biological networks rather than individual genes. It supports the extensive genetic, epigenetic and phenotypic heterogeneity implicated in schizophrenia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-015-0093-1) contains supplementary material, which is available to authorized users.

Abnormal immune system development and function in schizophrenia helps reconcile diverse findings and suggests new treatment and prevention strategies

Extensive research implicates disturbed immune function and development in the etiology and pathology of schizophrenia. In addition to reviewing evidence for immunological factors in schizophrenia, this paper discusses how an emerging model of atypical immune function and development helps explain a wide variety of well-established - but puzzling - findings about schizophrenia. A number of theorists have presented hypotheses that early immune system programming, disrupted by pre- and perinatal adversity, often combines with abnormal brain development to produce schizophrenia. The present paper focuses on the hypothesis that disruption of early immune system development produces a latent immune vulnerability that manifests more fully after puberty, when changes in immune function and the thymus leave individuals more susceptible to infections and immune dysfunctions that contribute to schizophrenia. Complementing neurodevelopmental models, this hypothesis integrates findings on many contributing factors to schizophrenia, including prenatal adversity, genes, climate, migration, infections, and stress, among others. It helps explain, for example, why (a) schizophrenia onset is typically delayed until years after prenatal adversity, (b) individual risk factors alone often do not lead to schizophrenia, and (c) schizophrenia prevalence rates actually tend to be higher in economically advantaged countries. Here we discuss how the hypothesis explains 10 key findings, and suggests new, potentially highly cost-effective, strategies for treatment and prevention of schizophrenia. Moreover, while most human research linking immune factors to schizophrenia has been correlational, these strategies provide ethical ways to experimentally test in humans theories about immune function and schizophrenia. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Genetic studies of schizophrenia: an update

Schizophrenia (SCZ) is a complex and heterogeneous mental disorder that affects about 1% of global population. In recent years, considerable progress has been made in genetic studies of SCZ. A number of common variants with small effects and rare variants with relatively larger effects have been identified. These variants include risk loci identified by genome-wide association studies, rare copy-number variants identified by comparative genomic analyses, and de novo mutations identified by high-throughput DNA sequencing. Collectively, they contribute to the heterogeneity of the disease. In this review, we update recent discoveries in the field of SCZ genetics, and outline the perspectives of future directions.

Fetal programming of schizophrenia: select mechanisms

Mounting evidence indicates that schizophrenia is associated with adverse intrauterine experiences. An adverse or suboptimal fetal environment can cause irreversible changes in brain that can subsequently exert long-lasting effects through resetting a diverse array of biological systems including endocrine, immune and nervous. It is evident from animal and imaging studies that subtle variations in the intrauterine environment can cause recognizable differences in brain structure and cognitive functions in the offspring. A wide variety of environmental factors may play a role in precipitating the emergent developmental dysregulation and the consequent evolution of psychiatric traits in early adulthood by inducing inflammatory, oxidative and nitrosative stress (IO&NS) pathways, mitochondrial dysfunction, apoptosis, and epigenetic dysregulation. However, the precise mechanisms behind such relationships and the specificity of the risk factors for schizophrenia remain exploratory. Considering the paucity of knowledge on fetal programming of schizophrenia, it is timely to consolidate the recent advances in the field and put forward an integrated overview of the mechanisms associated with fetal origin of schizophrenia.

Excess of homozygosity in the major histocompatibility complex in schizophrenia

Genome-wide association studies (GWAS) in schizophrenia have focused on additive allelic effects to identify disease risk loci. In order to examine potential recessive effects, we applied a novel approach to identify regions of excess homozygosity in an ethnically homogenous cohort: 904 schizophrenia cases and 1640 controls drawn from the Ashkenazi Jewish (AJ) population. Genome-wide examination of runs of homozygosity identified an excess in cases localized to the major histocompatibility complex (MHC). To refine this signal, we used the recently developed GERMLINE algorithm to identify chromosomal segments shared identical-by-descent (IBD) and compared homozygosity at such segments in cases and controls. We found a significant excess of homozygosity in schizophrenia cases compared with controls in the MHC (P-value = 0.003). An independent replication cohort of 548 schizophrenia cases from Japan and 542 matched healthy controls demonstrated similar effects. The strongest case-control recessive effects (P = 8.81 × 10(-8)) were localized to a 53-kb region near HLA-A, in a segment encompassing three poorly annotated genes, TRIM10, TRIM15 and TRIM40. At the same time, an adjacent segment in the Class I MHC demonstrated clear additive effects on schizophrenia risk, demonstrating the complexity of association in the MHC and the ability of our IBD approach to refine localization of broad signals derived from conventional GWAS. In sum, homozygosity in the classical MHC region appears to convey significant risk for schizophrenia, consistent with the ecological literature suggesting that homozygosity at the MHC locus may be associated with vulnerability to disease.

Dual cases of type 1 narcolepsy with schizophrenia and other psychotic disorders

OBJECTIVE

Cases of narcolepsy in association with psychotic features have been reported but never fully characterized. These patients present diagnostic and treatment challenges and may shed new light on immune associations in schizophrenia.

METHOD

Our case series was gathered at two narcolepsy specialty centers over a 9-year period. A questionnaire was created to improve diagnosis of schizophrenia or another psychotic disorder in patients with narcolepsy. Pathophysiological investigations included full HLA Class I and II typing, testing for known systemic and intracellular/synaptic neuronal antibodies, recently described neuronal surface antibodies, and immunocytochemistry on brain sections to detect new antigens.

RESULTS

Ten cases were identified, one with schizoaffective disorder, one with delusional disorder, two with schizophreniform disorder, and 6 with schizophrenia. In all cases, narcolepsy manifested first in childhood or adolescence, followed by psychotic symptoms after a variable interval. These patients had auditory hallucinations, which was the most differentiating clinical feature in comparison to narcolepsy patients without psychosis. Narcolepsy therapy may have played a role in triggering psychotic symptoms but these did not reverse with changes in narcolepsy medications. Response to antipsychotic treatment was variable. Pathophysiological studies did not reveal any known autoantibodies or unusual brain immunostaining pattern. No strong HLA association outside of HLA DQB1*06:02 was found, although increased DRB3*03 and DPA1*02:01 was notable.

CONCLUSION

Narcolepsy can occur in association with schizophrenia, with significant diagnostic and therapeutic challenges. Dual cases maybe under diagnosed, as onset is unusually early, often in childhood. Narcolepsy and psychosis may share an autoimmune pathology; thus, further investigations in larger samples are warranted.

Neuroimmunological aberrations and cerebral asymmetry abnormalities in schizophrenia: select perspectives on pathogenesis

Within the wide-ranging gamut of factors that comprise gene-environment interactions postulated to underlie schizophrenia, the crosstalk between environmental factors and feto-maternal immune components has been put forth as one of the important mechanisms that increase the risk towards schizophrenia in the offspring. Interestingly, immune factors have been shown to critically modulate the brain development during the prenatal stages. Moreover the past many decades, influential theoretical propositions and evidence base (albeit not unequivocally) have compellingly linked prenatal sex hormonal status to critically provoke long lasting immunological changes and subsequently affect developmental programming of cerebral asymmetry in schizophrenia. In this review, we summarize the select perspectives emphasizing the role of neuroimmunoendocrine pathways in anomalous cerebral asymmetry in contemporary understanding of schizophrenia pathogenesis.

Genome-wide association studies: findings at the major histocompatibility complex locus in psychosis

The major histocompatibility complex (MHC) is one of the most intensively investigated, genetically diverse regions of the genome. In its extended form, it encodes more than 400 genes critical to immunity but is also involved in many other functions. In 2009, three simultaneously published genome-wide association studies (GWAS) reported the first compelling evidence for involvement of the MHC in schizophrenia susceptibility. In this review, we describe the structure and function of the MHC, discuss some of the challenges for genetic analysis of the region, and provide an update on findings from GWAS studies before describing potential approaches to interpreting the role of the locus in schizophrenia etiology. The GWAS literature supports involvement of the MHC locus in schizophrenia susceptibility. Current evidence suggests that the MHC plays a more significant role in schizophrenia susceptibility than in other psychiatric disorders. Because of the substantial diversity at the locus, there are differences in the implicated risk variants between ancestral groups, as there are for many other disorders. This is somewhat different than the pattern emerging at other loci. The association findings presently capture large genomic regions, with at least some evidence to suggest that multiple signals may be involved. Based on notable successes in other disorders, we suggest approaches to refining association signals at the locus. Finally, we discuss that these genetic data may be used to understand how the MHC contributes to the complex etiology of schizophrenia.

Major histocompatibility complex I in brain development and schizophrenia

Although the etiology of schizophrenia (SZ) remains unknown, it is increasingly clear that immune dysregulation plays a central role. Genome-wide association studies reproducibly indicate an association of SZ with immune genes within the major histocompatibility complex (MHC). Moreover, environmental factors that increase risk for SZ, such as maternal infection, alter peripheral immune responses as well as the expression of immune molecules in the brain. MHC class I (MHCI) molecules might mediate both genetic and environmental contributions to SZ through direct effects on brain development in addition to mediating immunity. MHCI molecules are expressed on neurons in the central nervous system throughout development and into adulthood, where they regulate many aspects of brain development, including neurite outgrowth, synapse formation and function, long-term and homeostatic plasticity, and activity-dependent synaptic refinement. This review summarizes our current understanding of MHCI expression and function in the developing brain as well as its involvement in maternal immune activation, from the perspective of how these roles for MHCI molecules might contribute to the pathogenesis of SZ.

A critical review of pro-cognitive drug targets in psychosis: convergence on myelination and inflammation

Antipsychotic drugs have thus far focused on dopaminergic antagonism at the D2 receptors, as counteracting the hyperdopaminergia in nigrostriatal and mesolimbic projections has been considered mandatory for the antipsychotic action of the drugs. Current drugs effectively target the positive symptoms of psychosis such as hallucinations and delusions in the majority of patients, whereas effect sizes are smaller for negative symptoms and cognitive dysfunctions. With the understanding that neurocognitive dysfunction associated with schizophrenia have a greater impact on functional outcome than the positive symptoms, the focus in pharmacotherapy for schizophrenia has shifted to the potential effect of future drugs on cognitive enhancement. A major obstacle is, however, that the biological underpinnings of cognitive dysfunction remain largely unknown. With the availability of increasingly sophisticated techniques in molecular biology and brain imaging, this situation is about to change with major advances being made in identifying the neuronal substrates underlying schizophrenia, and putative pro-cognitive drug targets may be revealed. In relation to cognitive effects, this review focuses on evidence from basic neuroscience and clinical studies, taking two separate perspectives. One perspective is the identification of previously under-recognized treatment targets for existing antipsychotic drugs, including myelination and mediators of inflammation. A second perspective is the development of new drugs or novel treatment targets for well-known drugs, which act on recently discovered treatment targets for cognitive enhancement, and which may complement the existing drugs. This might pave the way for personalized treatment regimens for patients with schizophrenia aimed at improved functional outcome. The review also aims at identifying major current constraints for pro-cognitive drug development for patients with schizophrenia.

Narcolepsy-cataplexy and schizophrenia in adolescents

BACKGROUND

Despite advances in the understanding of narcolepsy, little information the on association between narcolepsy and psychosis is available, except for amphetamine-related psychotic reactions. Our case-control study aimed to compare clinical differences and analyze risk factors in children who developed narcolepsy with cataplexy (N-C), schizophrenia, and N-C followed by schizophrenia.

METHODS

Three age- and gender-matched groups of children with N-C schizophrenia (study group), N-C (control group 1), and schizophrenia only (control group 2) were investigated. Subjects filled out sleep questionnaires, sleep diaries, and quality of life scales, followed by polysomnography (PSG), multiple sleep latency tests (MSLT), routine blood tests, HLA typing, genetic analysis of genes of interest, and psychiatric evaluation. The risk factors for schizophrenia also were analyzed.

RESULTS

The study group was significantly overweight when measuring body mass index (BMI) (P=.016), at narcolepsy onset compared to control group 1, and the study group developed schizophrenia after a mean of 2.55±1.8 years. Compared to control group 2, psychotic symptoms were significantly more severe in the study group, with a higher frequency of depressive symptoms and acute ward hospitalization in 8 out of 10 of the subjects. They also had poorer long-term response to treatment, despite multiple treatment trials targeting their florid psychotic symptoms. All subjects with narcolepsy were HLA DQ B1(∗)0602 positive. The study group had a significantly higher frequency of DQ B1(∗)-03:01/06:02 (70%) than the two other groups, without any significant difference in HLA-DR typing, tumor necrosis factor α (TNF-α) levels, hypocretin (orexin) receptor 1 gene, HCRTR1, and the hypocretin (orexin) receptor 2 gene, HCRTR2, or blood infectious titers.

CONCLUSION

BMI and weight at onset of narcolepsy as well as a higher frequency of DQ B1(∗)-03:01/06:02 antigens were the only significant differences in the N-C children with secondary schizophrenia; such an association is a therapeutic challenge with long-term persistence of severe psychotic symptoms.

Coding and noncoding gene expression biomarkers in mood disorders and schizophrenia

Mood disorders and schizophrenia are common and complex disorders with consistent evidence of genetic and environmental influences on predisposition. It is generally believed that the consequences of disease, gene expression, and allelic heterogeneity may be partly the explanation for the variability observed in treatment response. Correspondingly, while effective treatments are available for some patients, approximately half of the patients fail to respond to current neuropsychiatric treatments. A number of peripheral gene expression studies have been conducted to understand these brain-based disorders and mechanisms of treatment response with the aim of identifying suitable biomarkers and perhaps subgroups of patients based upon molecular fingerprint. In this review, we summarize the results from blood-derived gene expression studies implemented with the aim of discovering biomarkers for treatment response and classification of disorders. We include data from a biomarker study conducted in first-episode subjects with schizophrenia, where the results provide insight into possible individual biological differences that predict antipsychotic response. It is concluded that, while peripheral studies of expression are generating valuable results in pathways involving immune regulation and response, larger studies are required which hopefully will lead to robust biomarkers for treatment response and perhaps underlying variations relevant to these complex disorders.

The spatio-temporal expression of MHC class I molecules during human hippocampal formation development

In the immune system, the major histocompatibility complex (MHC) class I molecules mediate both the innate and adaptive immune responses in vertebrates. There has been a dogma that the central nervous system (CNS) is immune privileged and healthy neurons do not express MHC class I molecules. However, recent studies have indicated that the expression and non-immunobiologic roles of MHC class I in mammalian CNS. But data referring to humans are scarce. In this study we report the expression and cellular localization of MHC class I in the human fetal, early postnatal and adult hippocampal formation. The expression of MHC class I was very low in the hippocampus at 20 (gestational weeks) GW and slowly increased at 27-33 GW. The gradually increased expression in the somata of some granular cells in dentate gyrus (DG) was observed at 30-33 GW. Whereas, a rapid increase in MHC class I molecules expression was found in the subiculum and it reached high levels at 31-33 GW and maintained at postnatal 55 days. No expression of MHC class I was found in hippocampal formation in adult. MHC class I heavy chain and β2 microglobulin (β2M) showed similar expression in some cells of the hippocampal formation at 30-33 GW. Moreover, MHC class I molecules were mainly expressed in neurons and most MHC class I-expressing neurons were glutamatergic. The temporal and spatial patterns of MHC class I expression appeared to follow gradients of pyramidal neurons maturation in the subiculum at prenatal stages and suggested that MHC class I molecules are likely to regulate neuron maturation. This article is part of a Special Issue entitled Priority to Publish.

The TRIPS (Toll-like receptors in immuno-inflammatory pathogenesis) Hypothesis: a novel postulate to understand schizophrenia

Mounting evidence indicates that immune activation and/or immuno-inflammatory reactions during neurodevelopment apparently contribute to the pathogenesis and progression of schizophrenia. One of the important environmental factors that is known to trigger immune activation/inflammatory responses during early pregnancy is prenatal infection. Recent understanding from animal studies suggests that prenatal infection induced maternal immune activation (MIA)/inflammation in congruence with oxidative/nitrosative stress can lead to neurodevelopmental damage and behavioral abnormalities in the offspring. Although the underlying precise mechanistic processes of MIA/inflammation are yet to be completely elucidated, it is being increasingly recognized that Toll-like receptors (TLRs) that form the first line of defense against invading microorganisms could participate in the prenatal infection induced immune insults. Interestingly, some of the TLRs, especially TLR3 and TLR4 that modulate neurodevelopment, neuronal survival and neuronal plasticity by regulating the neuro-immune cross-talk in the developing and adult brain could also be affected by prenatal infection. Importantly, sustained activation of TLR3/TLR4 due to environmental factors including infection and stress has been found to generate excessive reactive oxygen species (ROS)/reactive nitrogen species (RNS) as well as pro-inflammatory mediators during embryogenesis, which result into neuronal damage by necrosis/apoptosis. In recent times, ROS/RNS and immuno-inflammatory mediators are being increasingly linked to progressive brain changes in schizophrenia. Although a significant role of TLR3/TLR4 in neurodegeneration is gaining certainty, their importance in establishing a causal link between prenatal infection and immuno-inflammatory, oxidative and nitrosative stress (IO&NS) responses and influence on adult presentation of schizophrenia is yet to be ascertained. We review here the current knowledge generated from the animal and human studies on the role of TLRs in schizophrenia and finally propose the "TRIPS Hypothesis" (Toll-like receptors in immuno-inflammatory pathogenesis) to elucidate the underlying mechanism(s) of TLR-mediated risk of schizophrenia. Considering the established role of TLR3 and TLR4 in antiviral and antibacterial responses respectively, we believe that in some cases of schizophrenia where IO&NS responses are evident, prenatal infection might lead to neuroprogressive changes in a TLR3/TLR4-dependent way.

Evidence for a dysregulated immune system in the etiology of psychiatric disorders

There is extensive bi-directional communication between the brain and the immune system in both health and disease. In recent years, the role of an altered immune system in the etiology of major psychiatric disorders has become more apparent. Studies have demonstrated that some patients with major psychiatric disorders exhibit characteristic signs of immune dysregulation and that this may be a common pathophysiological mechanism that underlies the development and progression of these disorders. Furthermore, many psychiatric disorders are also often accompanied by chronic medical conditions related to immune dysfunction such as autoimmune diseases, diabetes and atherosclerosis. One of the major psychiatric disorders that has been associated with an altered immune system is schizophrenia, with approximately one third of patients with this disorder showing immunological abnormalities such as an altered cytokine profile in serum and cerebrospinal fluid. An altered cytokine profile is also found in a proportion of patients with major depressive disorder and is thought to be potentially related to the pathophysiology of this disorder. Emerging evidence suggests that altered immune parameters may also be implicated in the neurobiological etiology of autism spectrum disorders. Further support for a role of immune dysregulation in the pathophysiology of these psychiatric disorders comes from studies showing the immunomodulating effects of antipsychotics and antidepressants, and the mood altering effects of anti-inflammatory therapies. This review will not attempt to discuss all of the psychiatric disorders that have been associated with an augmented immune system, but will instead focus on several key disorders where dysregulation of this system has been implicated in their pathophysiology including depression, schizophrenia and autism spectrum disorder.