TLR9 and infection: To further investigate whether HD-13 activates MAPK and NF-κB pathways by accelerating TLR9 expression, thereby activating inflammatory response in 3D4/21 cells, following infection with HD-13 or TLR9 silencing in 3D4/21 cells, Western blot was performed to measure the levels of MAPK pathway-related proteins, including ERK, p-ERK, p38, p-p38, JNK, and p-JNK.