Subunit and whole molecule specificity of the anti-bovine casein immune response in recent onset psychosis and schizophrenia

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Abstract

Previous studies show increased antibody levels to bovine casein in some individuals with schizophrenia. The immunogenicity of specific domains of bovine casein varies among people with milk sensitivities and thus could vary among different neuropsychiatric disorders. Using ELISAs and immunoblotting, we characterized IgG class antibody specificity to whole bovine casein and to the αs, β, and κ subunits in individuals with recent onset psychosis (n = 95), long-term schizophrenia (n = 103), and non-psychiatric controls (n = 65). In both patient groups, we found elevated IgG to casein proteins, particularly to whole casein and the αs subunit (p  0.0001). Odds ratios of casein seroprevalence for recent onset psychosis (age-, gender-, race-, smoking-adjusted) were significant for whole casein (8.13, p  0.0001), and the αs (7.89, p  0.0001), β (5.23, p  0.001) and κ (5.70, p  0.0001) subunits. Odds ratios for long-term schizophrenia were significant for whole casein (7.85, p  0.0001), and the αs (4.78, p  0.003) and κ (4.92, p  0.004) subunits. Within the recent onset group, odds ratios were particularly significant for a subgroup of people with psychotic disorders that included major depressive disorders (8.22–16.48, p  0.0001). In a different recent onset subgroup (schizophrenia-spectrum disorders), PANSS scores for negative symptoms were correlated with casein antibody levels for the αs and κ subunits (p  0.001–0.01). Immunoblotting patterns also exhibited group specificity, with κ predominant in recent onset and αs in schizophrenia (Fisher's Exact Test, p  0.001). The elevated IgG and unique patterns of antibody specificity to bovine casein among diagnostic groups provide a rationale for clinical trials to evaluate efficacies of dietary modifications in individuals with neuropsychiatric diseases.

Introduction

In individuals with schizophrenia, elevations in IgG and IgA antibodies to casein- and gluten-derived proteins have been reported (Cascella et al., 2009, Dohan et al., 1972, Dohan and Grasberger, 1973, Kinnell et al., 1982, Reichelt et al., 1996, Reichelt and Landmark, 1995, Samaroo et al., 2009, Sugerman et al., 1982). The mechanisms behind this association are not known with certainty but may involve differences in the immune response to circulating antigens or alterations in the proteolytic processing and intestinal absorption of ingested proteins (Dohan, 1966, Dohan, 1979, Dohan et al., 1972, Dohan and Grasberger, 1973).

The casein complex forms a micelle that represents approximately 80% of the total protein content found in milk (Farrell et al., 2004). There are four subunits (αs1, αs2, β, κ) of casein, but how these subunits interact in a tertiary structure has not yet been definitively proven (Johansson et al., 2009). Understanding the three-dimensional arrangement of the casein micelle is an active research area, because industrialized milk processing is known to change the structure and hence the immunogenicity of different parts of the milk molecule (Nentwich et al., 2004). The immunogenic potential of specific domains of the bovine casein molecule varies among people with milk sensitivities and allergies (Lin et al., 2009, Sletten et al., 2007a, Sletten et al., 2007b). If people with neuropsychiatric diseases have a greater immune reaction against bovine casein than do non-psychiatric controls, it would be helpful to identify if it is the whole casein molecule or a specific region or subunit that is particularly immunogenic. In turn, processes applied to milk formulations could be further refined to possibly eliminate or modify amino acid sequences that represent immunogenic components.

We developed immunoassays and quantified IgG antibody levels to whole bovine casein and to the αs, β, and κ subunits in individuals with a recent onset of psychosis, long-term schizophrenia, and controls who had no history of psychiatric disorder. Our approach also included a qualitative immunoblotting component that allowed visualization of immunoreactivity to the purified subunits of bovine casein as well as to peptide fragments related to each subunit. The identification of immunoreactive peptide derivatives of the main subunit proteins would be informative for determining if additional breakdown products may contribute to the anti-bovine casein immune response.

Section snippets

Study participants

Ninety-five individuals with a recent onset of psychosis, 103 individuals with long-term schizophrenia and 65 individuals who had no history of psychiatric disorders were recruited for this study. The methods for identifying and characterizing individuals of the diagnostic groups according to criteria defined by DSM-IV have been previously described (Dickerson et al., 2003, Dickerson et al., 2007, Dickerson et al., 2008, Severance et al., 2009).

For individuals with a recent onset of psychosis,

Results

We measured the levels of IgG antibodies to whole casein and to three casein subunits in 95 individuals with recent onset psychosis, 103 individuals with long-term schizophrenia and 65 non-psychiatric controls. The results of these assays are depicted in Fig. 1. We found that the three diagnostic groups differed significantly in antibody levels against whole casein (ANOVA F-stat = 17.17, df = 262, p  0.00001), the αs subunit (ANOVA F-stat = 9.17, df = 262, p  0.0001), the β subunit (ANOVA F-stat = 4.93, df =

Discussion

In this study, we documented significantly increased levels of antibodies to bovine casein and casein subunits in individuals with recent onset psychosis and long-term schizophrenia. This anti-bovine casein immune response is particularly robust in a subgroup of patients, and epitopes on different casein subunits are recognized. The intact casein molecule proved especially immunogenic in the ELISA studies, followed in intensity by the αs and κ subunits, and this finding was consistent for both

Role of funding source

Funding for this study was provided by the Stanley Medical Research Institute. The funding source had no involvement in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Contributors

E. Severance and R. Yolken designed the study with input from F. Dickerson, I. Bossis, and J.C. Xiao. All authors were involved in data acquisition, analyses and interpretation. E. Severance wrote the first draft of the manuscript with input from F. Dickerson and R. Yolken. All authors contributed to and have approved the final manuscript.

Conflicts of interest

All of the authors declare that they have no conflicts of interest.

Acknowledgements

The authors thank Ann Cusic for administrative support.

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