title: Inflammatory cytokine alterations in schizophrenia: a systematic quantitative review.
abstract: BACKGROUND
  Cytokines play an important role in infection and inflammation and are crucial mediators of the cross-talk between the brain and the immune system. Schizophrenia would be associated with an imbalance in inflammatory cytokines, leading to a decrease in Th1 and an increase in Th2 cytokine secretion. However, data published so far have been inconsistent. The primary objective of the present meta-analysis was to verify whether the cytokine imbalance hypothesis of schizophrenia is substantiated by evidence.
  
  
  METHODS
  Cross-sectional studies were included if they assessed in vivo plasma or serum cytokine concentrations and/or in vitro secretion of cytokines by peripheral blood leukocytes from schizophrenia patients and healthy volunteers.
  
  
  RESULTS
  Data from 62 studies involving a total sample size of 2298 schizophrenia patients and 1858 healthy volunteers remained for analysis. Ten cytokines were assessed, including the prototypic Th1 and Th2 cytokines gamma interferon (IFN-gamma) and interleukin 4 (IL-4) as well as IL-2, soluble IL-2 receptor (sIL-2R), IL-1beta, IL-1 receptor antagonist (IL-1RA), tumor necrosis factor-alpha (TNF-alpha), IL-6, soluble IL-6 receptor (sIL-6R), and IL-10. The results show that an increase occurs in in vivo IL-1RA, sIL-2R, and IL-6 and a decrease occurs in in vitro IL-2 in schizophrenia. No significant effect sizes were obtained for the other cytokines.
  
  
  CONCLUSIONS
  These findings provide the first evidence of establishment of an inflammatory syndrome in schizophrenia, which refutes the current hypothesis of a Th2 slant. Caveats are presented to data interpretation, including the role of stress and the effect of weight gain that develops in schizophrenia.
authors.affiliation: Department of Psychiatry, Faculty of Medicine, University of Montreal, Fernand-Seguin Research Center, Louis-H Lafontaine Hospital, Montreal, Quebec, Canada.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Potvin
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Stip
authors.forename: Amir A
authors.initials: AA
authors.lastname: Sepehry
authors.forename: Alain
authors.initials: A
authors.lastname: Gendron
authors.forename: Ramatoulaye
authors.initials: R
authors.lastname: Bah
authors.forename: Edouard
authors.initials: E
authors.lastname: Kouassi
mesh_terms: D020274:Autoimmune Diseases of the Nervous System / Q000175:diagnosis / Q000276:immunology; D016207:Cytokines / Q000097:blood*; D006801:Humans; D018836:Inflammation Mediators / Q000097:blood*; D012016:Reference Values; D012559:Schizophrenia / Q000175:diagnosis / Q000276:immunology*; D018417:Th1 Cells / Q000276:immunology; D018418:Th2 Cells / Q000276:immunology
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators