Increased peripheral CD4⁺ lymphocytes promote ketamine-induced abnormal behaviors in mice

Ketamine (Ket) is a globally widely used injectable anesthetic and recreational drug that can lead to persistent behavioral deficits and induce psychotic states. Immune pathogenesis is believed to play a pivotal role in psychological symptoms and abnormal behavior. However, the role of the immune system, particularly peripheral immune changes, in ketamine-induced behavioral deficits and even psychotic symptoms remains largely elusive. This study aimed to explore the potential role of the peripheral immune system in ketamine-induced behavioral abnormalities in mice. Continuous administration of high-dose ketamine in C57/B6J mice induced abnormalities representative of anxiety-depressive-like behavior or memory-cognitive behavior, accompanied by morphological changes, elevated levels of inflammatory cytokines, and enhanced expression of markers representing astrocyte activity in the hippocampus and prefrontal cortex. Furthermore, flow cytometry was used to analyze changes in the number and composition of immune cells in the peripheral blood of mice after high-dose ketamine administration. The results showed a significant increase in peripheral T lymphocytes, especially CD4⁺ lymphocytes, while NK cells and B lymphocytes did not exhibit significant changes. Additionally, there was a significant increase of CD4⁺ lymphocytes in the hippocampus and prefrontal cortex of the mice. Based on these findings, in vivo neutralization of CD4⁺ lymphocytes surprisingly reversed the anxiety-depressive-like behavior or memory-cognitive behavior of the mice and partially or fully restored brain tissue morphology and the expression of astrocyte activity molecules. Our results indicate that peripheral CD4⁺ lymphocytes play a crucial role in ketamine-induced behavioral abnormalities, and the presence of CD4⁺ lymphocytes may participate in and promote ketamine-induced anxiety, depressive-like behavior, and memory-cognitive dysfunction.