Despite over 100-year history of research on schizophrenia, its etiology is still not fully understood, which might be due to the significant heterogeneity in terms of both its course, as well as the etiopathogenesis. One of the best-proven mediating mechanisms in the development of schizophrenia is the immuno-inflammatory response, the sources of which are believed to be the dysfunctions of brain-gut axis and pathological processes occurring in the intestines. This paper is a review of the literature on this subject which presents factors both involved in the functioning of brain-gut axis and important for the development of schizophrenia, i.e. 1. intestinal microbiome (intestinal microbiota), 2. permeable intestine (leaky gut syndrome), 3. hypersensitivity to food antigens, including gluten and casein of cow's milk. Research results seem to be very promising and indicate the possibility of improved clinical outcomes in some patients with schizophrenia by modifying diet, use of probiotics, and the implementation of antibiotic therapy of specific treatment groups. However, further research is needed on links between the intestinal microbiome and intestinal function as factors mediating the activation of the immune system and the development and further course of schizophrenia.

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Schizophrenia is a heterogeneous disorder without a fully elucidated etiology and mechanisms. One likely explanation for the development of schizophrenia is low-grade inflammation, possibly caused by processes in the gastrointestinal tract related to gluten sensitivity. The aims of this study were to: (1) compare levels of markers of gluten sensitivity, inflammation and gut permeability, and (2) determine associations between gluten sensitivity, inflammation, and intestinal permeability in patients with first-episode/chronic (FS/CS) schizophrenia and healthy individuals (HC). The total sample comprised 162 individuals (52 FS; 50 CS, and 60 HC). The examination included clinical variables, nutritional assessment, and serum concentrations of: high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), soluble CD14 (sCD14), anti-Saccharomyces cerevisiae antibody (ASCA), antigliadin antibodies (AGA) IgA/IgG, antibodies against tissue transglutaminase 2 (anti-tTG) IgA, anti-deamidated gliadin peptides (anti-DGP) IgG. A significant difference between groups was found in sCD14, ASCA, hs-CRP, IL-6 and AGA IgA levels. AGA IgG/IgA levels were higher in the FS (11.54%; 30.77%) and CS (26%; 20%) groups compared to HC. The association between intestinal permeability and inflammation in the schizophrenic patients only was noted. The risk for developing schizophrenia was odds ratio (OR) = 4.35 (95% confidence interval (CI 1.23–15.39) for AGA IgA and 3.08 (95% CI 1.19–7.99) for positive AGA IgG. Inflammation and food hypersensitivity reactions initiated by increased intestinal permeability may contribute to the pathophysiology of schizophrenia. The immune response to gluten in FS differs from that found in CS.