Serum IL-17A and CCL20 levels and their correlation with obsessive-compulsive disorder and suicidality in schizophrenia and bipolar mood disorder

BACKGROUND: IL-17A and CCL20 are key inflammatory mediators involved in neuroinflammation linked to schizophrenia (SCZ) and bipolar mood disorder (BMD), influencing disease severity and representing potential biomarkers and therapeutic targets. This study aimed to assess serum IL-17A and CCL20 levels in SCZ and BMD patients and explore their associations with obsessive-compulsive disorder (OCD) symptoms and suicidality. METHODS: A cross-sectional study was conducted in 2024 at Ibn Sina Psychiatric Hospital, Mashhad, Iran, involving inpatients diagnosed with SCZ or BMD during acute episodes. Consecutive sampling was used to enroll eligible patients aged 18 to 65 who met the inclusion criteria, excluding those with substance use disorders, autoimmune diseases, recent infections, or on immunosuppressive therapy. Demographic and clinical data, including OCD and suicidality status, were collected via interviews and medical records. Serum IL-17A and CCL20 levels were measured using ELISA kits after overnight fasting. Statistical analyses included t-tests, Mann-Whitney U, chi-square, logistic regression, and generalized linear model tree (GLMtree) models, considering a p-value of less than 0.05 as statistically significant. RESULTS: The study included patients with a mean age of 39.81 ± 10.36 years. BMD patients showed greater employment rates and more suicidal thoughts (p < 0.001). Serum IL-17A and CCL20 levels did not differ significantly between SCZ and BMD groups. Logistic regression revealed a probability inverse association between IL-17A and suicidal thoughts in BMD patients (β = -0.406). GLMtree analysis demonstrated that increased IL-17A was probably associate with greater OCD severity in females and a complex interaction with electroconvulsive therapy (ECT) history, while seemingly IL-17A's association with suicidal thoughts differed by diagnosis, ethnicity, and medication use (p < 0.05). CONCLUSION: The study found that suicidal thoughts and suicide cases were more common in BMD patients. Although serum IL-17A and CCL20 levels did not differ between SCZ and BMD groups, lower IL-17A were associated with greater suicidality in BMD. The relationship between IL-17A, OCD, and suicidal ideation was maybe influenced by gender, ethnicity, treatment, and diagnosis, underscoring the complex immune-psychiatric interactions in these disorders.