Abstract:
Toll-like receptors (TLRs) are well-characterized pattern recognition receptors of innate immunity,
known to induce immune responses against the pathogens by interacting with evolutionarily conserved
pathogen-associated molecular patterns (PAMPs). In this study, a novel TLR homolog from disk abalone
(Haliotis discus discus) was identified and characterized at molecular level. The open reading frame (ORF)
of AbTLR is 3804 bp in length and encodes a 1268 amino acid peptide with a calculated molecular mass of
143.5 kDa. The deduced protein shows typical TLR domain architecture, with leucine rich repeats (LRR)
and the toll-interleukin receptor (TIR) domain. Phylogenetic analysis revealed a close evolutionary
relationship for AbTLR to its invertebrate counterparts, with close clustering to the molluscan homologs.
Quantitative real-time PCR detected ubiquitous transcription of AbTLR in healthy tissues, but with highest
levels in hemocytes. Differential transcriptional modulation of AbTLR was observed in abalone hemocytes
and gills upon immune challenge, whereby Vibrio parahaemolyticus and purified lipopolysaccharide (LPS)
enhanced the transcript level prominently. In addition, the viral hemorrhagic septicemia virus induced
AbTLR transcription in hemocytes and gills, representing the first evidence of viral-induced immune
response in mollusks to date. Collectively, our findings support a putative role for AbTLR in abalone
antiviral and antibacterial defense.
