The possible reasons were as follows: 1) Th17 cells secreted interleukin-17A, which enhanced the release of neurotransmitters in the medial prefrontal cortex, leading to brain injury by inducing the structural remodeling of microglia and promoting a continuous inflammatory reaction, thus causing anxiety and depression (28,29); or 2) Th17 cells might regulate cognitive function by regulating hippocampal neurogenesis, neuroinflammation, etc. (30,31). The gene discussed is IL17A; the disease is major depressive disorder.