Latent infection, inflammatory markers and suicide attempt history in depressive disorders

Background: Numerous reports have described increased rates of exposure to Toxoplasma gondii levels in individuals with a history of suicide attempts in comparison with well controls, or psychiatrically ill individuals, with no suicide attempt history. Such findings suggest that the behavioral effects this parasite exerts on rodent hosts extends to humans though few studies have searched for underlying mechanisms. Methods: The present study compared 96 patients with an active depressive disorder and a history of at least two suicide attempts to 126 depressed patients with no history of suicide attempts by IgG and IgM levels of Toxoplasma gondii and cytomegalovirus (CMV). The groups were also compared by IL_1b, TNF-alpha, CRP, IL_6, and IL_1ra titers. Results: Toxoplasma gondii IgM levels were higher, and seropositivity more likely, in the suicide attempt group. CMV IgG levels were also higher among suicide attempters. Several of these immunoglobulin measures were more robustly associated with the number of suicide attempts than with the dichotomy of suicide attempter and non-attempter. These two antibody levels were also additive in their association with suicide attempter status. IL_1a levels were lower in suicide attempters and correlated negatively with levels of antibodies to Toxoplasma gondii and CMV. Limitations: These include a sample size insufficient to explore differences across mood disorder diagnoses or demographic groupings. Conclusions: These results indicate that exposure to common infectious agents such as Toxoplasma gondii and CMV are associated with increased risk of suicide attempts but the mechanism of association does not appear to involve the activation of cytokines. Elucidation of the mechanisms which define the relationship between infections and suicide attempts may lead to new methods for the prediction and prevention of suicide attempts.