Priority communicationStudies characterizing 60 kda autoantibodies in subjects with schizophrenia
Introduction
Schizophrenia is a heterogeneous syndrome most likely caused by a variety of different etiopathogenic mechanisms. Our current diagnosis is based on categorizing the signs and symptoms of the syndrome, which limits our ability to reliably identify biological findings for schizophrenia and to develop specific treatments for the syndrome. Therefore, identifying biological markers that categorize a subset of subjects in a consistent fashion might facilitate future investigations of the pathogenesis of this syndrome and might enhance our ability to treat some subjects with schizophrenia.
Studies attempting to link immune dysregulation to schizophrenia have been ongoing for more than a century Ganguli et al 1993, Ganguli et al 1994, Kirch 1993, Muller et al 2000, Noy et al 1994, Yolken and Torrey 1995. As our understanding of the immune system has progressed, the sophistication of these investigations has changed dramatically. Many of the earlier studies were surveys of lymphocyte counts from psychiatric subjects. These studies suggested that there might be a lymphocytosis associated with acute psychosis Bruce and Peebles 1903, Bruce and Peebles 1904, Jankovic 1985, Kim et al 2001. There were also some initial studies suggesting that autoantibodies that react with the brain may be present in the serum of some subjects with schizophrenia Henneberg et al 1994, Jankovic and Djordjijevic 1991, Lehmann-Facius 1937, Mukherjee et al 1994, Teplizki et al 1992, Yang et al 1994. Studies of immune activation and schizophrenia were further complicated by the advent of antipsychotic medication, because the phenothiazine and clozapine medications modulate immune function Rapaport et al 1991, Zarrabi et al 1979. Recent studies have employed more sophisticated methodologies, such as flow cytometry, enzyme linked immunoassays (ELISAs), and other molecular biological techniques to investigate blood samples and cerebrospinal fluid (CSF). These techniques have facilitated the evaluation of different components of the immune system, including cytokines, cytokine receptor levels, adhesion molecules, and activation factors Delrahim and Rapaport 2001, Muller et al 2000, Rapaport and Muller 2001.
One of the most extensively investigated components of this interface between the immune system and psychiatry research has been the search for autoantibodies in subjects with schizophrenia. These serum and CSF investigations frequently attempted to determine whether subjects with schizophrenia had an increased prevalence of antibodies directed against proteins extracted from cell lines, animal brain tissue, or viral antigens. As would be expected in research investigating a complex syndrome, the findings are equivocal Henneberg et al 1993, Henneberg et al 1994, Klyushnik et al 1999, Leonardi and Cocito 1982, Mazeh et al 1998, Pandey et al 1981, Rimon et al 1986, Teplizki et al 1992, Torrey et al 1978, Zarrabi et al 1979. We were intrigued by a report by Kilidireas et al (1992) suggesting that there was an increased prevalence of antibodies directed against 60-kilodalton (kDa) heat shock protein (HSP60) in the serum of subjects with schizophrenia. Although the initially reported high prevalence rate could not be replicated by either Kilidireas and colleagues or Schwarz and colleagues, groups continued to report the presence of anti-HSP60 antibodies in the serum of subjects with schizophrenia Kilidireas et al 1992, Kim et al 2001, Schwarz et al 1999. Leykin and colleagues have also used HSP60 as an adjuvant in lymphocyte cultures and found that schizophrenic subjects had greater immune stimulation (Leykin et al 1999), thus suggesting again that the presence of this molecular chaperone may be immunogenic for some subjects with schizophrenia.
Our conceptual framework is based on the antigen-driven hypothesis of autoimmunity (Tan 1991). We believe that the increased prevalence of antibodies in the serum binding to the 60 kDa region is caused by the aberrant expression of these proteins in some individuals with schizophrenia. At this point we do not know whether these proteins are being expressed as a stress response against an ongoing pathologic process or as a response to the stress of psychosis in a subset of subjects. For example, antibodies directed against molecular chaperones, such as the heat shock protein family, may be indicative of a subgroup of subjects with schizophrenia who, in response to their illness, elicit this innate protective effect. The presence of antibodies to these heat shock proteins might then serve as useful biological markers for a subgroup of subjects with schizophrenia. Therefore, we hypothesized that there would be an increased prevalence of antibodies in the serum of subjects with schizophrenia that bind to proteins migrating at 60 kDa when compared with matched normal volunteers. We further postulated that there would be a specific increase in the prevalence of anti-HSP60 antibodies in subjects with schizophrenia. An additional goal of this project was to identify and characterize other potential antigens that migrate at 60 kDa.
Section snippets
Human subjects
The study was approved by the Institutional Review Board of the Human Research Protections Program at the University of California, San Diego. Written, informed consent was obtained from each human subject participating in this study after the study procedures had been fully explained by research staff. In the case of subjects who were under a conservatorship, informed consent was also obtained from the conservator. Each schizophrenic subject received a complete psychiatric assessment and
Results
Fifteen percent (17/117) of sera from the schizophrenic subjects but only 3% (2/62) of sera from the normal volunteers showed reactivity with a 60 kDa protein band on Western blotting [χ2(1) = 4.4, p = .037]. Figure 1 shows the reactivity to the 60 kDa proteins of some representative sera from subjects with schizophrenia (lanes 1–6) and normal volunteers (lanes 7–9). Western blotting analysis using recombinant HSP60 was carried out to verify that the 60 kDa target protein observed in this study
Discussion
One of the major challenges faced by immunologic investigations of schizophrenia has been reproducibility. In this study, we attempted to replicate and extend the work of Kilidireas et al (1992) with a large sample of well-defined schizophrenic subjects and normal volunteers. We demonstrated that schizophrenic subjects are more likely to have antibodies that bind to proteins migrating at 60 kDa (15%) than are normal volunteers (3%). Using purified recombinant human heat shock protein as
Acknowledgements
This work was supported by a National Alliance for Research on Schizophrenia and Depression Independent Investigator Award; a National Institute on Mental Health Schizophrenia and Immune Activation Grant (MH49746–05); a Veterans Affairs Medical Research Service Merit Review Grant; and a Stanley Foundation Grant.
This work was presented as a poster at the Society for Biological Psychiatry meeting in 2000; and has been discussed at the seventh International Meeting on Psychoneuroimmunology in
References (52)
- et al.
A restricted cytoplasmic region of IL-2 receptor beta chain is essential for growth signal transduction but not for ligand binding and internalization
Cell
(1989) - et al.
Increased prevalence of antibrain antibodies in the sera from schizophrenic patients
Schizophr Res
(1994) - et al.
Proteins of the Myc networkEssential regulators of cell growth and differentiation
Adv Cancer Res
(1996) From immunoneurology to immunopsychiatryNeuromodulating activity of anti-brain antibodies
Int Rev Neurobiol
(1985)- et al.
Antibodies to the human 60 kDa heat-shock protein in patients with schizophrenia
Lancet
(1992) - et al.
Identification of antibodies to heat shock proteins 90 kDa and 70 kDa in patients with schizophrenia
Schizophr Res
(2001) - et al.
The effects of psychological stress on humansIncreased production of pro-inflammatory cytokines and a Th1-like response in stress-induced anxiety
Cytokine
(1998) - et al.
Antibodies to neuroblastoma cell line proteins in patients with schizophrenia
J Neuroimmunol
(1998) - et al.
Three distinct IL-2 signaling pathways mediated by bcl-2, c-myc, and lck cooperate in hematopoietic cell proliferation
Cell
(1995) - et al.
Serum antibodies to nicotinic acetylcholine receptors in schizophrenic patients
Schizophr Res
(1994)