Reduced total complement haemolytic activity in schizophrenic patients

The role of Toll-like receptors in neuropsychiatric disorders: Immunopathology, treatment, and management

Neuropsychiatric disorders denote a broad range of illnesses involving neurology and psychiatry. These disorders include depressive disorders, anxiety, schizophrenia, bipolar disorder, attention deficit hyperactivity disorder, autism spectrum disorders, headaches, and epilepsy. In addition to their main neuropathology that lies in the central nervous system (CNS), lately, studies have highlighted the role of immunity and neuroinflammation in neuropsychiatric disorders. Toll-like receptors (TLRs) are innate receptors that act as a bridge between the innate and adaptive immune systems via adaptor proteins (e.g., MYD88) and downstream elements; TLRs are classified into 13 families that are involved in normal function and illnesses of the CNS. TLRs expression affects the course of neuropsychiatric disorders, and is influenced during their pharmacotherapy; For example, the expression of multiple TLRs is normalized during the major depressive disorder pharmacotherapy. Here, the role of TLRs in neuroimmunology, treatment, and management of neuropsychiatric disorders is discussed. We recommend longitudinal studies to comparatively assess the cell-type-specific expression of TLRs during treatment, illness progression, and remission. Also, further research should explore molecular insights into TLRs regulation and related pathways.

The plasma level of complement component 4A decreases with aripiprazole treatment in patients with early psychosis

The complement component 4 (C4) gene has been reported to be significantly associated with schizophrenia, and C4A RNA expression was found to increase in postmortem brains of schizophrenia patients. This study aimed to examine the plasma levels of C4A and C4B proteins in patients with early psychosis and their changes following aripiprazole treatment. We recruited 45 patients, including 17 patients with ultra-high-risk and 28 patients with first-episode psychosis, and 45 age-matched and sex-matched controls. All patients received aripiprazole treatment for 4 weeks. Each patient received symptom evaluation before and after the treatment period. We measured the plasma levels of C4A and C4B in the pretreatment and posttreatment stages of patients and controls using an enzyme-linked immunosorbent assay. We found no significant differences in C4A and C4B levels between patients and controls, but the C4A level decreased significantly with aripiprazole treatment. Multivariate analysis showed that the decrease rate of C4A was significantly associated with the treatment response of the positive symptom dimension. In summary, we found that the plasma level of C4A decreased with aripiprazole treatment, and the decrease rate was associated with the treatment response of the positive dimension in patients with early psychosis. This mechanism deserves further clarification.

Plasma complement component 4 alterations in patients with schizophrenia before and after antipsychotic treatment

This study was performed to investigate the plasma C4 level and the influence of antipsychotic medication in schizophrenic patients. Thirty-six schizophrenic patients were followed-up for a mean of four weeks. The plasma level of C4 in schizophrenia was significantly higher than that in healthy controls at baseline, and was significantly decreased after antipsychotic treatment. CRP at both baseline and follow-up in patients were comparable to that in healthy controls. Our findings indicate that the plasma level of C4 is increased in schizophrenia patients at the acute stage of illness and can be decreased by antipsychotic medication.

Peripheral complement is increased in schizophrenia and inversely related to cortical thickness

BACKGROUND

There is growing evidence for complement system involvement in the pathophysiology of schizophrenia, although the extent and magnitude of complement factor disturbances has not been fully reported. It also remains unclear whether complement abnormalities are characteristic of all patients with schizophrenia or whether they are representative of a subgroup of patients who show signs of heightened inflammation. The aim of the present study was to quantify and compare the levels of a range of complement factors, receptors and regulators in healthy controls and people with schizophrenia and to determine the extent to which the levels of these peripheral molecules relate to measures of brain structure, particularly cortical thickness.

METHOD

Seventy-five healthy controls and 90 patients with schizophrenia or schizoaffective disorder were included in the study. Peripheral blood samples were collected from all participants and mRNA expression was quantified in 20 complement related genes, four complement proteins, as well as for four cytokines. T1-weighted structural MRI scans were acquired and analysed to determine cortical thickness measures.

RESULTS

There were significant increases in peripheral mRNA encoding receptors (C5ar1, CR1, CR3a), regulators (CD55, C59) and protein concentrations (C3, C3b, C4) in people with schizophrenia relative to healthy controls. C4a expression was significantly increased in a subgroup of patients displaying elevated peripheral cytokine levels. A higher inflammation index score derived from mRNA expression patterns predicted reductions in cortical thickness in the temporal lobe (superior temporal gyrus, transverse temporal gyrus, fusiform gyrus, insula) in patients with schizophrenia and healthy controls.

CONCLUSIONS

Analysis of all three major complement pathways supports increased complement activity in schizophrenia and also shows that peripheral C4a up-regulation is related to increased peripheral pro-inflammatory cytokines in healthy controls. Our region-specific, neuroimaging findings linked to an increased peripheral complement mRNA expression pattern suggests a role for complement in cortical thinning. Further studies are required to further clarify clinical and neurobiological consequences of aberrant complement levels in schizophrenia and related psychoses.

Levels of lymphocyte-associated regulators of complement system CD55 and CD59 are changed in schizophrenia patients

OBJECTIVE

Although pathological mechanisms of schizophrenia are unknown, evidence in the literature suggests that the immune system might be involved in the pathogenesis. Complement is an important part of the immune system and it has been suggested to play role in the pathogenesis of schizophrenia. We aimed to investigate the potential involvement of the complement system in schizophrenia by the determination of peripheral concentrations of certain complement proteins and their regulators in patients.

METHODS

Plasma concentrations of complement C3, C4, and C1 inhibitory protein were measured by chemiluminescence in 41 schizophrenia patients and 39 healthy controls. Expression of CD55, CD59, and CD46 proteins on peripheral blood mononuclear cells were determined by flow cytometry in the same groups.

RESULTS

Frequencies of peripheral immune cells expressing CD55 were determined to be significantly higher in schizophrenia patients than in healthy people (p = 0.020). Frequencies of peripheral immune cells expressing CD59 was determined to be significantly higher in healthy people than in schizophrenia patients (p = 0.012). The expression level of CD55 per cell was measured to be significantly elevated in patients compared to healthy controls (p = 0.026).

CONCLUSIONS

Our data clearly demonstrate an elevated complement activity in schizophrenia and points to a possible complement association in the pathogenesis.Key pointsIncreased the expression level, and frequency of CD55 in schizophrenia patients.Decreased frequency of CD59 in schizophrenia patients.No difference in the expression level of CD59; the expression level, and frequency of CD46; frequency of complement C3, C4, and C1 inhibitory protein.

Aberrant Complement System Activation in Neurological Disorders

The complement system is an assembly of proteins that collectively participate in the functions of the healthy and diseased brain. The complement system plays an important role in the maintenance of uninjured (healthy) brain homeostasis, contributing to the clearance of invading pathogens and apoptotic cells, and limiting the inflammatory immune response. However, overactivation or underregulation of the entire complement cascade within the brain may lead to neuronal damage and disturbances in brain function. During the last decade, there has been a growing interest in the role that this cascading pathway plays in the neuropathology of a diverse array of brain disorders (e.g., acute neurotraumatic insult, chronic neurodegenerative diseases, and psychiatric disturbances) in which interruption of neuronal homeostasis triggers complement activation. Dysfunction of the complement promotes a disease-specific response that may have either beneficial or detrimental effects. Despite recent advances, the explicit link between complement component regulation and brain disorders remains unclear. Therefore, a comprehensible understanding of such relationships at different stages of diseases could provide new insight into potential therapeutic targets to ameliorate or slow progression of currently intractable disorders in the nervous system. Hence, the aim of this review is to provide a summary of the literature on the emerging role of the complement system in certain brain disorders.

Maternal Immune Activation and Schizophrenia-Evidence for an Immune Priming Disorder

Schizophrenia is a complex neurodevelopmental disorder affecting around 19. 8 million people worldwide. The etiology of the disorder is due to many interacting genetic and environmental factors, with no one element causing the full spectrum of disease symptoms. Amongst these factors, maternal immune activation (MIA) acting during specific gestational timings has been implicated in increasing schizophrenia risk in offspring. Epidemiological studies have provided the rationale for this link with prevalence of maternal infection correlating to increased risk, but these studies have been unable to prove causality due to lack of control of confounding factors like genetic susceptibility and inability to identify specific cellular and molecular mechanisms. Animal models have proved significantly more useful in establishing the extent to which MIA can predispose an individual to schizophrenia, displaying how maternal infection alone can directly result in behavioral abnormalities in rodent offspring. Alongside information from genome wide association studies (GWAS), animal models have been able to identify the role of complement proteins, particularly C4, and display how alterations in this system can cause development of schizophrenia-associated neuropathology and behavior. This article will review the current literature in order to assess whether schizophrenia can, therefore, be viewed as an immune priming disorder.

Peripheral complement proteins in schizophrenia: A systematic review and meta-analysis of serological studies

BACKGROUND

There is renewed focus on the complement system in the pathogenesis of schizophrenia. In addition to providing aetiological insights, consistently dysregulated complement proteins in serum or plasma may have clinical utility as biomarkers.

METHODS

We performed a systematic literature review searching PubMed, Embase and PsycINFO for studies measuring complement system activity or complement protein concentrations in serum or plasma from patients with schizophrenia compared to controls. Random-effects meta-analyses were performed to calculate pooled effect estimates (Hedges' g standardised mean difference [SMD]) for complement proteins whose concentrations were measured in three or more studies. The review was pre-registered on the PROSPERO database (CRD42018109012).

RESULTS

Database searching identified 1146 records. Fifty-eight full-text articles were assessed for eligibility and 24 studies included. Seven studies measured complement system activity. Activity of the classical pathway did not differ between cases and controls in four of six studies, and conflicting results were noted in two studies of alternative pathway activity. Twenty studies quantified complement protein concentrations of which complement components 3 (C3) and 4 (C4) were measured in more than three studies. Meta-analyses showed no evidence of significant differences between cases and controls for 11 studies of C3 (SMD 0.04, 95% confidence interval [CI] -0.29-0.36) and 10 studies of C4 (SMD 0.10, 95% CI -0.21-0.41).

CONCLUSIONS

Serological studies provide mixed evidence regarding dysregulation of the complement system in schizophrenia. Larger studies of a longitudinal nature, focusing on early phenotypes, could provide further insights regarding the potential role of the complement system in psychotic disorders.

Complement System in Brain Architecture and Neurodevelopmental Disorders

Current evidence indicates that certain immune molecules such as components of the complement system are directly involved in neurobiological processes related to brain development, including neurogenesis, neuronal migration, synaptic remodeling, and response to prenatal or early postnatal brain insults. Consequently, complement system dysfunction has been increasingly implicated in disorders of neurodevelopmental origin, such as schizophrenia, autism spectrum disorder (ASD) and Rett syndrome. However, the mechanistic evidence for a causal relationship between impaired complement regulation and these disorders varies depending on the disease involved. Also, it is still unclear to what extent altered complement expression plays a role in these disorders through inflammation-independent or -dependent mechanisms. Furthermore, pathogenic mutations in specific complement components have been implicated in the etiology of 3MC syndrome, a rare autosomal recessive developmental disorder. The aims of this review are to discuss the current knowledge on the roles of the complement system in sculpting brain architecture and function during normal development as well as after specific inflammatory insults, such as maternal immune activation (MIA) during pregnancy, and to evaluate the existing evidence associating aberrant complement with developmental brain disorders.

The complement system in schizophrenia: where are we now and what's next?

The complement system is a set of immune proteins involved in first-line defense against pathogens and removal of waste materials. Recent evidence has implicated the complement cascade in diseases involving the central nervous system, including schizophrenia. Here, we provide an up-to-date narrative review and critique of the literature on the relationship between schizophrenia and complement gene polymorphisms, gene expression, protein concentration, and pathway activity. A literature search identified 23 new studies since the first review on this topic in 2008. Overall complement pathway activity appears to be elevated in schizophrenia. Recent studies have identified complement component 4 (C4) and CUB and Sushi Multiple Domains 1 (CSMD1) as potential genetic markers of schizophrenia. In particular, there is some evidence of higher rates of C4B/C4S deficiency, reduced peripheral C4B concentration, and elevated brain C4A mRNA expression in schizophrenia patients compared to controls. To better elucidate the additive effects of multiple complement genotypes, we also conducted gene- and gene-set analysis through MAGMA which supported the role of Human Leukocyte Antigen class (HLA) III genes and, to a lesser extent, CSMD1 in schizophrenia; however, the HLA-schizophrenia association was likely driven by the C4 gene. Lastly, we identified several limitations of the literature on the complement system and schizophrenia, including: small sample sizes, inconsistent methodologies, limited measurements of neural concentrations of complement proteins, little exploration of the link between complement and schizophrenia phenotype, and lack of studies exploring schizophrenia treatment response. Overall, recent findings highlight complement components-in particular, C4 and CSMD1-as potential novel drug targets in schizophrenia. Given the growing availability of complement-targeted therapies, future clinical studies evaluating their efficacy in schizophrenia hold the potential to accelerate treatment advances.

The expression of toll-like receptors in peripheral blood mononuclear cells is altered in schizophrenia

Increasing evidence suggests that in addition to neurochemical abnormalities, various immunological alterations are related to the pathogenesis of schizophrenia. Toll-like receptors (TLRs) actively mediate immune/inflammatory processes and play a pivotal role in damage/danger recognizing. Therefore, the aim of this study was to compare the expression of TLRs in peripheral blood mononuclear cells (PBMCs) in schizophrenic patients with those of healthy subjects. It also measures the metabolic status of the study subjects. Twenty-seven adult European Caucasian patients with paranoid schizophrenia and twenty-nine healthy volunteers were included in this prospective study. qRT-PCR assessed TLR mRNA expression levels. Body composition was measured using two methods: bioimpedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA). The TLR1, TLR2, TLR4, TLR6, and TLR9 expression were down-regulated, in opposite to TLR3 and TLR7 which manifested higher expression in patients with schizophrenia. TLR5 and TLR8 mRNAs did not differ between groups. TLR mRNA expression was highly correlated. Decreased TLR expression may protect against excessive cell stimulation via exogenous and/or endogenous ligands, and may be recognized as a counterbalancing mechanism limiting the excessive development of inflammation.

Neuro-Immune Hemostasis: Homeostasis and Diseases in the Central Nervous System

Coagulation and the immune system interact in several physiological and pathological conditions, including tissue repair, host defense, and homeostatic maintenance. This network plays a key role in diseases of the central nervous system (CNS) by involving several cells (CNS resident cells, platelets, endothelium, and leukocytes) and molecular pathways (protease activity, complement factors, platelet granule content). Endothelial damage prompts platelet activation and the coagulation cascade as the first physiological step to support the rescue of damaged tissues, a flawed rescuing system ultimately producing neuroinflammation. Leukocytes, platelets, and endothelial cells are sensitive to the damage and indeed can release or respond to chemokines and cytokines (platelet factor 4, CXCL4, TNF, interleukins), and growth factors (including platelet-derived growth factor, vascular endothelial growth factor, and brain-derived neurotrophic factor) with platelet activation, change in capillary permeability, migration or differentiation of leukocytes. Thrombin, plasmin, activated complement factors and matrix metalloproteinase-1 (MMP-1), furthermore, activate intracellular transduction through complement or protease-activated receptors. Impairment of the neuro-immune hemostasis network induces acute or chronic CNS pathologies related to the neurovascular unit, either directly or by the systemic activation of its main steps. Neurons, glial cells (astrocytes and microglia) and the extracellular matrix play a crucial function in a “tetrapartite” synaptic model. Taking into account the neurovascular unit, in this review we thoroughly analyzed the influence of neuro-immune hemostasis on these five elements acting as a functional unit (“pentapartite” synapse) in the adaptive and maladaptive plasticity and discuss the relevance of these events in inflammatory, cerebrovascular, Alzheimer, neoplastic and psychiatric diseases. Finally, based on the solid reviewed data, we hypothesize a model of neuro-immune hemostatic network based on protein–protein interactions. In addition, we propose that, to better understand and favor the maintenance of adaptive plasticity, it would be useful to construct predictive molecular models, able to enlighten the regulating logic of the complex molecular network, which belongs to different cellular domains. A modeling approach would help to define how nodes of the network interact with basic cellular functions, such as mitochondrial metabolism, autophagy or apoptosis. It is expected that dynamic systems biology models might help to elucidate the fine structure of molecular events generated by blood coagulation and neuro-immune responses in several CNS diseases, thereby opening the way to more effective treatments.

Neuropil contraction in relation to Complement C4 gene copy numbers in independent cohorts of adolescent-onset and young adult-onset schizophrenia patients-a pilot study

A recent report suggested Complement 4 (C4A) gene copy numbers (GCN) as risk factors for schizophrenia. Rodent model showed association of C4 with synaptic pruning suggesting its pathophysiological significance (Sekar, A. et al. (2016)). We, therefore, predicted that C4A GCN would be positively correlated with neuropil contraction in the human brain among schizophrenia patients showing more prominent correlations in ventral regions among young adults and dorsal regions among adolescents since neuromaturation progresses dorsoventrally. Whole-brain, multi-voxel, in vivo phosphorus magnetic resonance spectroscopy (³¹P MRS) assessed neuropil changes by estimating levels of membrane phospholipid (MPL) precursors and catabolites. Increased MPL catabolites and/or decreased MPL precursors indexed neuropil contraction. Digital droplet PCR-based assay was used to estimate C4A and C4B GCN. We evaluated two independent cohorts (young adult-onset early-course schizophrenia (YASZ = 15) and adolescent-onset schizophrenia (AOSZ = 12) patients), and controls matched for each group, n = 22 and 15, respectively. Separate forward stepwise linear regression models with Akaike information Criterion were built for MPL catabolites and precursors. YASZ cohort: Consistent with the rodent model (Sekar, A. et al. 2016)), C4A GCN positively correlated with neuropil contraction (increased pruning/decreased formation) in the inferior frontal cortex and inferior parietal lobule. AOSZ cohort: C4A GCN positively correlated with neuropil contraction in the dorsolateral prefrontal cortex and thalamus. Exploratory analysis of C4B GCN showed positive correlation with neuropil contraction in the cerebellum and superior temporal gyrus among YASZ while AOSZ showed neuropil contraction in the prefrontal and subcortical structures. Thus, C4A and C4B GCN are associated with neuropil contraction in regions often associated with schizophrenia, and may be neuromaturationally dependent.

The complement system: a gateway to gene-environment interactions in schizophrenia pathogenesis

The pathogenesis of schizophrenia is considered to be multi-factorial, with likely gene-environment interactions (GEI). Genetic and environmental risk factors are being identified with increasing frequency, yet their very number vastly increases the scope of possible GEI, making it difficult to identify them with certainty. Accumulating evidence suggests a dysregulated complement pathway among the pathogenic processes of schizophrenia. The complement pathway mediates innate and acquired immunity, and its activation drives the removal of damaged cells, autoantigens and environmentally derived antigens. Abnormalities in complement functions occur in many infectious and autoimmune disorders that have been linked to schizophrenia. Many older reports indicate altered serum complement activity in schizophrenia, though the data are inconclusive. Compellingly, recent genome-wide association studies suggest repeat polymorphisms incorporating the complement 4A (C4A) and 4B (C4B) genes as risk factors for schizophrenia. The C4A/C4B genetic associations have re-ignited interest not only in inflammation-related models for schizophrenia pathogenesis, but also in neurodevelopmental theories, because rodent models indicate a role for complement proteins in synaptic pruning and neurodevelopment. Thus, the complement system could be used as one of the 'staging posts' for a variety of focused studies of schizophrenia pathogenesis. They include GEI studies of the C4A/C4B repeat polymorphisms in relation to inflammation-related or infectious processes, animal model studies and tests of hypotheses linked to autoimmune diseases that can co-segregate with schizophrenia. If they can be replicated, such studies would vastly improve our understanding of pathogenic processes in schizophrenia through GEI analyses and open new avenues for therapy.

The role of complement in neurological and neuropsychiatric diseases

The complement system is a major component of innate immunity and a potent driver of inflammation. It has key roles in host defense against pathogens but can also contribute to pathology by driving inflammation and cell damage in diverse diseases. Complement has emerged as an important factor in the pathogenesis of numerous diseases of the CNS and PNS, including infectious, autoimmune and degenerative disorders, and is increasingly implicated in neuropsychiatric disease. Establishing the roles and relevance of complement in disease pathogenesis has become ever more important in recent years as new drugs targeting the complement system have reached the clinic, and the potential for using complement analytes as disease biomarkers has been recognized. In this brief review, the author summarizes the evidence implicating complement in these diseases and outlines ways in which this new understanding can be used to aid diagnosis and improve outcome.

Bipolar and panic disorders may be associated with hereditary defects in the innate immune system

BACKGROUND

Mannan-binding lectin (MBL) and mannan-binding lectin-associated serine protease-2 (MASP-2) represent important arms of the innate immune system, and different deficiencies may result in infections or autoimmune diseases. Both bipolar and panic disorders are associated with increased inflammatory response, infections and mutual comorbidity. However, associations with MBL, MASP-2 or the gene, MBL2, coding for MBL, have not been investigated thoroughly.

METHODS

One hundred patients with bipolar disorder, 100 with panic disorder and 349 controls were included. Serum concentrations of MBL and MASP-2 were measured and seven single nucleotide polymorphisms (SNPs) influencing these concentrations were genotyped. Disease association with genetic markers and serum levels were investigated.

RESULTS

In panic disorder, we observed a large proportion (30%) of MBL deficient (<100ng/ml) individuals and significantly lower levels of MBL and MASP-2 plus association with the MBL2 YA two-marker haplotype. Bipolar disorder was associated with the MBL2 LXPA haplotype and lower MASP-2 levels.

LIMITATIONS

No information on course or severity of disorders was included, and only MBL and MASP-2 were measured, excluding other components from the complement pathway. Restrictions defined by ethnical committees preclude information of control׳s ethnic origin.

CONCLUSIONS

Significant differences in MBL and MASP-2 concentrations were observed between cohorts, especially an intriguing finding associating panic disorder with MBL deficiency. These differences could not be fully explained by allele or haplotype frequency variations. Since MBL deficiency is highly heterogeneous and associated with both infectious and autoimmune states, more research is needed to identify which complement pathway components could be associated with bipolar respectively panic disorder.

Inflammatory cytokine network in schizophrenia

OBJECTIVES

The purpose of this review is to analyse, sum up and discuss the available literature on the role of inflammation and inflammatory cytokines in the pathogenesis of schizophrenia.

METHODS

An electronic literature search of peer-reviewed English language articles using Pubmed was undertaken. These articles together with those published by us provided the background for the present review.

RESULTS

An overview of the available literature on this issue clearly demonstrated the alterations in mRNA and protein expression levels of several proinflammatory and chemotactic cytokines in patients with schizophrenia. Importantly, some of these changes are genetically determined. It was noteworthy that, depending on the study population, some variations of the data obtained are detected.

CONCLUSIONS

Altered inflammatory cytokine production, both genetically and environmentally determined, is implicated in schizophrenia and contributes to disease-associated low-grade systemic inflammation. Proinflammatory and chemotactic cytokines and their receptors may represent additional therapeutic targets for treatment of schizophrenia.

Label-free quantitative proteomic analysis reveals dysfunction of complement pathway in peripheral blood of schizophrenia patients: evidence for the immune hypothesis of schizophrenia

Schizophrenia is a complex mental disease caused by a combination of serial alterations in genetic and environmental factors. Although the brain is usually considered as the most relevant organ in schizophrenia, accumulated evidence suggests that peripheral tissues also contribute to this disease. In particular, abnormalities of the immune system have been identified in the peripheral blood of schizophrenia patients. To screen the serum proteomic signature of schizophrenia patients, we conducted shotgun proteomic analysis on serum samples of schizophrenia patients and healthy controls. High-abundance proteins were eliminated by immunoaffinity before LC-MS/MS analysis. The multivariate statistical test partial least squares-discriminant analysis (PLS-DA) was applied to build models for screening out variable importance in the projection (VIP) and 27 proteins were identified as being responsible for discriminating between the proteomic profiles of schizophrenia patients and healthy controls. Pathway analysis based on these 27 proteins revealed that complement and coagulation cascades was the most significant pathway. ELISA-based activity analyses indicated that the alternative complement pathway was suppressed in schizophrenia patients. Ingenuity pathways analysis was used to conduct the interaction network of 27 proteins. The network exhibited common features such as, nervous system development and function, humoral immune response and inflammatory response, and highlighted some proteins with important roles in the immune system, such as hub nodes. Our findings indicate dysregulation of the alternative complement pathway in schizophrenia patients. The protein interaction network enhances the interpretation of proteomic data and provides evidence that the immune system may contribute to schizophrenia.

Complement C4B protein in schizophrenia

Partial and/or complete deficiency of the complement protein C4 is associated with autoimmune and infectious diseases. Infectious or autoimmune processes may have a role in schizophrenia. Previous reports suggest abnormalities in the complement C4B isotype in schizophrenia and other mental disorders. We assessed C4A and C4B isotypes and serum C4B protein concentration in Armenian schizophrenic patients. Although there was no difference in frequency of C4BQ0, C4B serum protein level was significantly decreased in the schizophrenic patients compared with healthy controls.

The complement system in schizophrenia

Several lines of evidence suggest that immunological factors contribute to schizophrenia. Since 1989, the role of complement, a major effector of innate immunity and an adjuvant of adaptive immunity, has been explored in schizophrenia. Increased activity of C1, C3, C4 complement components in schizophrenia has been reported by two or more groups. Two studies on different subject cohorts showed increased MBL-MASP-2 activity in patients versus controls. More then one report indicated a significant high frequency of FB*F allotype and low prevalence of the FS phenotype of complement factor B in schizophrenia. From the data reported, it is likely that the disorder is accompanied by alterations of the complement classical and lectin pathways, which undergo dynamic changes, depending on the illness course and the state of neuro-immune crosstalk. Recent findings, implicating complement in neurogenesis, synapse remodeling and pruning during brain development, suggest a reexamination of the potential role of complement in neurodevelopmental processes contributing to schizophrenia susceptibility. It is plausible that the multicomponent complement system has more than one dimensional association with schizophrenia susceptibility, pathopsychology and illness course, understanding of which will bring a new perspective for possible immunomodulation and immunocorrection of the disease.

Increased complement classical and mannan-binding lectin pathway activities in schizophrenia

Schizophrenia is a severe mental disorder, with worldwide prevalence of 1-1.5%. Immunological research in schizophrenia indicates that infectious or autoimmune processes might play a role in the etiopathogenesis. The complement system is a major mediator of innate immune defence against infection and contributes to many functions of the immune system including inflammation, opsonization and cell lysis. Mannan-binding lectin (MBL) activates the complement system via the lectin pathway. Inherited MBL deficiency, common in most human populations, predisposes to infectious and autoimmune diseases. We measured total complement activity (CH50), C4 activity (C4 CH50), MBL level and the activities of MBL-associated serine proteases, MASP-1 and MASP-2 in sera of 45 schizophrenic patients and in 62 healthy volunteers. We found that schizophrenic patients and healthy volunteers have statistically similar MBL levels and MASP-1 activity. However, MBL-bound MASP-2 activity and therefore MBL and MASP-2-mediated complement activation capacity is increased in schizophrenic patients compared with healthy volunteers (P<0.01). The increase was accompanied by increased CH50 (P<0.02) and C4 CH50 (P<0.02). Our results support the idea that complement system alterations may be involved in schizophrenia.

Classical pathway complement activity in schizophrenia

There is considerable evidence to suggest a role for complement in the pathogenesis of schizophrenia, but the data related to the classical pathway complement activity in patients with schizophrenia are conflicting. In the present study, the total hemolytic activity of the complement and the activities of individual complement components, C1, C2, C3 and C4, were determined in the blood serum of schizophrenic patients with positive family history of the disease and healthy subjects. In comparison to the healthy subjects, the mean values of the hemolytic activities of the C1, C3 and C4 complement components in the serum of the schizophrenic patients were significantly higher, and the mean value of the hemolytic activity of the C2 complement component was significantly lower. However, no significant difference was found between the mean values of the total hemolytic activity of complement in schizophrenic patients and healthy subjects. The C3 hemolytic activity was 2.17 times higher in medicated patients than in drug-free patients. Within each group examined no significant difference was found between smokers and non-smokers or between males and females. The results of this study suggest that the pathogenesis of schizophrenia is associated with alterations in activities of complement classical pathway components.

Immunity and schizophrenia: autoimmunity, cytokines, and immune responses

As is evident from the present account, there is no single or persuasive argument that signals emanating from the immune system are directly involved in the etiology of schizophrenia. We do not even know if we are dealing with a single disorder with a single causality; almost certainly we are not. The precise etiology of schizophrenia, as with so many neurological disorders, remains obscure. However, there is abundant evidence in schizophrenia of mutual dysregulation of neuronal function and immune system activity. Although this evidence is not always consistent, a pattern emerges suggesting aspects of immune activity being involved in the pathology of neuronal development that characterizes schizophrenia. Exposure to infective agents, HLA associations, autoimmune associations, disturbances in lymphocyte populations, and cytokine imbalances with a skew toward Th2 activity are supportive of this view. That the evidence is not always consistent is a testament to the complexity and heterogeneity of the disorder, to confounding by antipsychotics that themselves are immunomodulatory, and to the multifaceted nature, with all its checks and balances, of the immune system itself.

Serological observations in patients suffering from acute manic episodes

Although abnormalities of the immune system have been described in depression, information on serological alteration in acutely manic patients has been scarce. The present study undertook to investigate the levels of C-reactive proteins, circulating immune complexes, total immunoglobulins and immunoglobulin subclasses, complement proteins C3, C4, C6 and Factor B in the sera of 45 patients suffering from an acute manic episode. The findings were compared with assessments on the sera of 45 controls. The results demonstrate a number of significant differences between patients and controls. Whilst levels of immunoglobulin D were significantly lower, the levels of total immunoglobulin and immunoglobulin G1, complement proteins C3, C6 and Factor B were raised in the patient group when compared with the controls. Our results suggest a relationship between acute mania and immunological parameters associated with acute phase responses.

Antinuclear autoantibodies in chronic schizophrenia

We determined the presence of antinuclear autoantibodies (ANA), antinative DNA and histone-reactive ANA in 3 groups of chronic schizophrenic patients (n=85): haloperidol-treated patients (for at least 3 months) (n=35), drug-free for at least 3 months (n=35) and neuroleptic-naive patients (n=15). The autoantibody titers were compared with those of healthy controls (n=37). A significantly higher frequency of positive ANA was found among chronic schizophrenic patients (approximately 20%) as compared with the controls (approximately 5%), irrespective of drug treatment, sex and age. No antinative ANA autoantibodies or histone reactive ANA were detected in either schizophrenic patients or controls. Further studies are needed to isolate and characterize in ANA-positive schizophrenic patients a putative specific ANA profile.