Lipopolysaccharide-induced innate immune factors in the bottlenose dolphin (Tursiops truncatus) detected in expression sequence tag analysis.

EST analysis based on the megaclone-megasorting method was performed using leukocytes from the bottlenose dolphin (Tursiops truncatus) with or without LPS stimulation. A total of 849 upregulated and 384 downregulated EST clones were sequenced, annotated, and functionally classified. Ferritin heavy peptide I was the most abundant upregulated transcript, suggesting that LPS stimulation induced high production of reactive oxygen species, which were sequestered in ferritin. Among the immune factors, the transcripts coding for an IL-1Ra, homologs to bovine serum amyloid A3, and canine intercellular adhesion molecule-1 were highly expressed. Markedly downregulated transcripts of immune factors were those for homologs of calcium-binding proteins belonging to the S100 family, S100A12, S100A8, and S100A6. Time-course experiments on the expression of some immune factors including IL-1Ra suggested that these factors interact and control cetacean innate immunity.

Cetacean Toll-like receptor 4 and myeloid differentiation factor 2, and possible cetacean-specific responses against Gram-negative bacteria.

Toll-like receptor 4 (TLR4) and myeloid differentiation factor 2 (MD-2) are essential for recognizing the lipopolysaccharides (LPS) of Gram-negative bacteria. We determined the sequences of cDNAs encoding TLR4 and MD-2 from cetaceans and generated three-dimensional (3D) models for a better understanding of their modes of interaction and LPS recognition. The 3D reconstructions showed that cetacean TLR4 and MD-2 formed a horseshoe-like structure comprised of parallel ß-strands and a ß-cup structure consisting of two anti-parallel ß-sheets, respectively. The (TLR4-MD-2)(2) duplex-heterodimer was shown to form a symmetrical structure. Comparison with the interfaces of the complexes in other mammals revealed that cetacean TLR4s have some amino acid residue substitutions involved in duplex-heterodimer formation and in species variation for LPS recognition. These substitutions in the changed amino acid residues may alter the interaction among TLR4, MD-2, and LPS and modify the TLR4/MD-2 immunological responses.