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 clinical 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 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 significant inverse association between IL-17A and suicidal thoughts in BMD patients (β = -0.406). GLMtree analysis demonstrated that increased IL-17A was linked to greater OCD severity in females and a complex interaction with ECT history, while 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 was significantly linked to increased suicidality in BMD. The relationship between IL-17A, OCD, and suicidal ideation was also influenced by gender, ethnicity, treatment, and diagnosis, underscoring the complex immune-psychiatric interactions in these disorders.