VIP and infection: The expression of the receptor of VIP, the vasoactive intestinal peptide receptor 1 (VPAC1, NM_214036), was both up-regulated after F4ab and F4ac ETEC separate infection, leading to a down-regulated expression of TLR4. (II) To maintain the homeostasis of the IPEC-J2 cells, some epigenetic mechanisms, like histone deacetylation and DNA methylation, down-regulated the expression of TLR4[49].