Molecular cloning and functional characterization of porcine MyD88 essential for TLR signaling.

We isolated cDNA encoding porcine MyD88 (poMyD88) from Peyer's patches (Pps) of GALT. The complete open reading frame (ORF) of poMyD88 contains 879 bp encoding a deduced 293 aa residues. The amino acid sequence of poMyD88 was characterized by N-terminal death, intermediate and C-terminal Toll/IL-1 receptor (TIR) domains. The putative poMyD88 protein shares a higher level of homology with its human (87.2% amino acid identity) than with its mouse (77.4% amino acid identity) counterpart. Overexpression of poMyD88 participated in the further enhanced activation of NF-kappaB in human embryonic kidney (HEK) 293 cells expressing porcine TLR2 and porcine TLR4/MD-2, but not porcine RP105/MD-1 after stimulation with the corresponding ligands. The expression levels of MyD88 were highest in the spleen and mesenteric lymph nodes (MLNs), and lower in digestive tissues of newborn swine. In adult swine, the expression levels in the digestive tissues were lower than those in MLNs and the spleen. These results suggest that an MyD88-dependent signaling pathway is present in newborn as well as in adult swine and that it is involved in the innate immune system of these animals.