CCR9 and infection: The KEGG pathway analysis identified eight significant signaling pathways with a p value < 0.05 (Figure 4B), among which the cytokine–cytokine receptor interaction (including CXCR3, CXCR6, CCR4, CCR5, CCR7, CCR9), chemokine signaling (including Src, Tiam1, PLCβ, RasGRP2), T cell receptor signaling (including CD247, CD3d, CD3e, CD3g, CTLA4, LCK, PLG2) and natural killer (NK) cell mediated cytotoxicity (including FASLG, SH2D1A, SH2D1B, GZMB, TNFSF10, ZAP70) were directly related to infection and immune response.