CD4 and infection: In addition, after infection with T. gondii, CD4+ T cells and CD8+ T cells secrete inflammatory factors such as TNF-α and IL-1 to stimulate microglia, and interfere with gamma-aminobutyric acid (GABA) and 5-hydroxytryptamine (5-HT) synthesis via the KYNA pathway (Mukhopadhyay et al., 2020; Yin et al., 2022).