Although the highest numbers of studies linking an infectious agent with schizophrenia has involved the parasite Toxoplasma gondii, the mechanistic underpinnings of this correlation has remained unaddressed. Incidentally, CD8 T cells, which play a pivotal role in mediating long-term immunity to Toxoplasma, are downregulated in schizophrenia patients. Recent studies have demonstrated that CD8 response is also impaired during chronic toxoplasmosis in murine models. In light of these new findings, in this article, we discuss the potential role of CD8 T cells in causing altered mental status in Toxoplasma seropositive schizophrenia patients.
Bipolar disorder is the least Studied among the three major psychiatric disorders of schizophrenia, major depression and bipolar disorder. Furthermore, investigations on infection and immunity in bipolar disorder make up only a small portion of the sparse research done on this disorder. However, there are reports that modulation of the immune system and certain infections might be associated with bipolar disorder and that there might be differences between bipolar and the other disorders. The purpose of this paper is to briefly review published data on these issues in bipolar versus the other disorders, and to present an ongoing clinical study on the putative involvement of infection with the parasite Toxoplasma gondii in these three major psychiatric disorders.