The plasma level of complement component 4A decreases with aripiprazole treatment in patients with early psychosis

•The plasma level of C4A decreases with aripiprazole treatment in early psychosis.•The decrease rate of C4A is associated with the treatment response of the positive symptom dimension in early psychosis.•The levels of C4A and C4B are not different between early psychosis and controls. The complement component 4 (C4) gene has been reported to be significantly associated with schizophrenia, and C4A RNA expression was found to increase in postmortem brains of schizophrenia patients. This study aimed to examine the plasma levels of C4A and C4B proteins in patients with early psychosis and their changes following aripiprazole treatment. We recruited 45 patients, including 17 patients with ultra-high-risk and 28 patients with first-episode psychosis, and 45 age-matched and sex-matched controls. All patients received aripiprazole treatment for 4 weeks. Each patient received symptom evaluation before and after the treatment period. We measured the plasma levels of C4A and C4B in the pretreatment and posttreatment stages of patients and controls using an enzyme-linked immunosorbent assay. We found no significant differences in C4A and C4B levels between patients and controls, but the C4A level decreased significantly with aripiprazole treatment. Multivariate analysis showed that the decrease rate of C4A was significantly associated with the treatment response of the positive symptom dimension. In summary, we found that the plasma level of C4A decreased with aripiprazole treatment, and the decrease rate was associated with the treatment response of the positive dimension in patients with early psychosis. This mechanism deserves further clarification.