Proinflammatory cytokines and their membrane-bound receptors are altered in the lymphocytes of schizophrenia patients
Introduction
It has been observed that the immune function, in general, and cytokine abnormalities in particular, are associated with the pathophysiology of schizophrenia (SZ) (Drexhage et al., 2010a, Hope et al., 2009, Zakharyan and Boyajyan, 2014). The abnormalities of the immune function in SZ are based on both direct and indirect evidence. For example, the administration of cytokines such as interferon (IFN) to rats causes a constellation of symptoms known as “sickness behavior” that includes cognitive changes, slowed cognitive speed, diminished social interactions, and reduced locomotor activity and executive functions (Dantzer et al., 1999). Also, the administration of cytokines, such as IFN to cancer patients induces symptoms known as sickness behavior (Capuron et al., 2001). Psychiatric side-effects associated with IFN therapy include anxiety, depression, psychosis, mania, and delirium (Cheng et al., 2009, Crane et al., 2003, Hosoda et al., 2000). The development of psychosis with IFN therapy has been reported and reviewed by Cheng et al. (2009).
That inflammatory processes are also involved in SZ (Dean, 2011) are based on the observation that proinflammatory cytokines, which are released from the immune cells as a result of inflammation or stress, are abnormal in the serum of patients with SZ (see reviews and meta-analyses by Modabbernia et al., 2013, Munkholm et al., 2013a, Munkholm et al., 2013b, Potvin et al., 2008). There are several studies, although not always consistent, that report increased levels of proinflammatory cytokines, such as IL-1β, IL-6, and TNF-α, and their soluble receptors in the serum of SZ patients (see review by Potvin et al., 2008).
Whereas proinflammatory cytokines and their soluble receptors are studied in SZ, the membrane-bound receptors, which are involved in mediating the biological and functions effects of cytokines have not been studied in the blood of SZ patients. Therefore, we examined if abnormality in gene expression of proinflammatory cytokines and their membrane-bound receptors may be associated with schizophrenic pathogenesis. We therefore determined the gene expression of the proinflammatory cytokines, IL-1β, IL-6, and TNF-α, and the cytokine receptors IL-1R1, IL-1R2, IL-1R antagonist (IL-1RA), IL-6R, IL-6 signal transducer (IL-6ST), also known as glycoprotein 130 (Gp130), TNFR1, and TNFR2 in the lymphocytes of SZ patients. To examine if changes in the mRNA levels of these proinflammatory cytokines are also associated with abnormalities of their protein expression levels, as reported by some investigators (Munkholm et al., 2013a, Munkholm et al., 2013b), we determined the protein expression levels of these proinflammatory cytokines in the plasma of SZ patients and NC control subjects.
Section snippets
Subjects
These studies were conducted in hospitalized patients with SZ (n = 30) admitted to the Psychiatric Clinical Research Center, a part of the General Clinical Research Center, University of Illinois at Chicago. This study was approved by the Institutional Review Board of the University of Illinois at Chicago. All subjects gave informed consent for the study.
After admission to the research unit, patients were kept drug-free up to two weeks before starting treatment. Blood samples were drawn from the
Demographic and clinical characteristics of SZ patients and NC subjects
The demographic and clinical characteristics of SZ patients and NC subjects are summarized in Table 2. There was no significant difference in the mean age between SZ patients and NC subjects. Gender distribution was similar between the two groups; however, race was not fully matched as there were more blacks in the patient group than in the control group. The mean in-hospital drug-free period was 4.29 ± 3.02 days.
mRNA expression levels of cytokine receptors in the lymphocytes of SZ patients and NC subjects
We determined the mRNA levels of membrane-bound receptors for IL-1, TNFα, and IL-6.
Discussion
In this study we found that the mRNA and protein levels of TNF-α and IL-6, but not IL-1β, were significantly increased in lymphocytes or plasma of SZ patients compared with NC subjects. We also found that the mRNA expression of IL-1R1, TNFR1, and TNFR2 was significantly higher in SZ patients compared with NC subjects, but the gene expression of IL-1R2, IL-1RA, IL-6, and Gp130 was not significantly different in SZ patients from that of NC subjects.
The biological effects of the cytokines are
Limitations
Our studies have some limitations. We do not have available data on body mass index (BMI) or on smoking history of the subjects and hence the effect of these variables on the cytokines and their receptors could not be ascertained. Also, although the samples size is adequate it is not large. This is primarily because we studied patients admitted to the research ward and not the outpatients. The other limitation is that the NC subjects and SZ patients are not very well matched for race.
Conclusions
To our knowledge, this is the first study of membrane-bound cytokine receptors in the blood of SZ patients, as only soluble receptors for these proinflammatory cytokines have been previously studied. Our studies indicate abnormal gene expression of some of these receptor subtypes in SZ patients. Since the functional consequences of proinflammatory cytokines and their soluble receptors are mediated through membrane-bound receptors involved in signaling mechanisms, it is crucial to study the
Role of funding source
This research was supported by a grant RO1-MH-56528 (Dr. Pandey) from the National Institute of Mental Health, Rockville, MD. This agency had no role in the study design, acquisition and interpretation of data or writing of the report.
Contributors
GNP had access to all data (reported and unreported) from the study and had complete freedom to direct its analysis and its reporting, without influence from the funding agency. He further affirms that there was no editorial direction or censorship from the sponsor. He was responsible for the conception of the study, had the lead in the analysis and interpretation of the data, and wrote the manuscript.
XR performed protein analyses of proinflammatory cytokines in plasma from schizophrenia (SZ)
Conflict of interest
All authors declare that they have no financial interests or potential conflicts of interest related directly or indirectly to this work.
Acknowledgments
We thank Runa Bhaumik, Ph.D. for her help with the statistical analyses.
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