Schizophrenia is a serious neuropsychiatric disease of uncertain etiology. We investigated the seropositivity rate for anti-Toxoplasma IgG and IgM antibodies by enzyme-linked immunosorbent assay (ELISA) in patients with schizophrenia to ascertain a possible relationship between Toxoplasma gondii and schizophrenia. We selected 100 patients with schizophrenia, 50 with depressive disorder, and 50 healthy volunteers to investigate the seropositivity rate of anti-Toxoplasma antibodies by ELISA. The seropositivity rate for anti-Toxoplasma IgG antibodies among schizophrenia patients (66%) was significantly higher than among patients with depressive disorder or healthy volunteers (P < .01). Thus, there might be a causal relationship between toxoplasmosis and the etiology of schizophrenia.

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Schizophrenia is one of the most severe psychiatric disorders, with a worldwide incidence of 1%. Immunological abnormalities have been found to be associated with schizophrenia for decades. Cytokines are key proteins involved in the immune system activation. Interleukin-10 (IL-10), an important immunoregulatory cytokine, is located on chromosome 1q31-32, a region previously reported to be linked to schizophrenia in genetic studies. In the present study it was aimed to examine the IL-10 gene promoter region's polymorphic variants in patients with schizophrenia in a population of the Elazig Region of East Anatolia, Turkey. Polymorphisms at position -1082, -819 and-592 in the IL-10 promoter region were determined in 171 Turkish patients who were diagnosed with schizophrenia, based on the DSM-IV, and 168 healthy controls, by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP). We analyzed allele, genotype, and haplotype distributions using a case-control association study. Genotyping was performed by RFLP. Statistically significant differences were observed in both allelic and genotypic frequencies of the-592A/C polymorphism (Allele, P=0.034, OR = 1.26, 95% CI 1.02-1.56; Genotype, P=0.048), while the other two polymorphisms in distribution of the alleles and genotypes in patients with schizophrenia were not significantly different from those of controls (P>0.05). Our results show a significant increase of GTA homozygotes (the high IL-10-producing haplotype) in schizophrenic patients compared to control subjects (P=0.0001). These data suggest that the IL-10 gene promoter polymorphism may be one of the susceptibility factors to develop schizophrenia in the Turkish population, and apparently in all humans.

Aims:  It has been hypothesized that the activation of the immune system may be involved in the neuropathological changes occurring in the central nervous system of schizophrenic patients. Cytokines play a key role in the activation of the immune system. Moreover, they strongly influence the dopaminergic, noradrenergic and serotonergic neurotransmission. To the best of our knowledge, in schizophrenic patients, plasma levels of interleukin (IL)‐12 were investigated only in one study, where deregulation of IL‐12 was determined. However, genotypical variations of the IL‐12B (p40) gene have not been investigated for schizophrenic patients yet. Therefore, in the present study, we aimed to examine polymorphic variants of IL‐12B (p40) gene promoter region in patients with schizophrenia in a population of the Elazig Region of East Anatolia, Turkey. Methods:  One hundred Turkish patients diagnosed with schizophrenia based on the Diagnostic and Statistical Manual of Mental Disorders (DSM‐IV), and 116 healthy control subjects participated in the present study. The genotype characteristics were determined by polymerase chain reaction‐based restriction fragment length polymorphism method using DNA extracted from peripheral blood. Results:  Significant differences in both the genotype and allele frequencies were found between schizophrenia patients and control groups (P < 0.01). Conclusions:  These findings may support the hypothesis that activation of the inflammatory response system and in particular, of Th‐1 cells, is involved in the pathophysiology of schizophrenia. We think that this study is the first trial associated with IL‐12 cytokine at the molecular genetic level on immune mechanisms for neuropsychiatric disorders including schizophrenia, and this perspective and the role of the cytokines in the pathogenesis of schizophrenia may constitute a reasonable target for the present and future treatment strategies and prognosis.