Identification and expression of Toll-like receptors 1–10 in selected bovine and ovine tissues

Members of the Toll-like receptor (TLR) family are vital to immune function through the sensing of pathogenic agents and initiation of an appropriate immune response. More specifically, tissue and cell specific TLR expression patterns have been correlated with the ability to respond to various pathogenic challenges. Bovine sequence exists for 4 of the 10 human TLR Reference Sequences and no ovine TLR sequence has been reported. The main goal of this study was to determine if homologues of human TLRs 1–10 exist within the cattle and sheep. Subsequent to this, quantitative real time PCR assays were to be developed to produce transcript expression profiles in cattle skin and sheep gut-associated lymphoid tissue, as these epithelial tissues are the primary sites of host/pathogen interactions for numerous pathogens. Our findings show that homologues of human TLRs 1–10 do indeed exist within both cattle and sheep, with respective bovine and ovine homologues sharing at least 95% nucleotide sequence identity and 83–90% identity to the corresponding human Reference Sequences. Conservation of the amino acid sequence between homologous ruminant and human TLRs ranged between 84 and 97%. Quantitative real time PCR (qPCR) assays confirmed expression of all 10 TLRs within ovine jejunum, Peyer's patch and mesenteric lymph nodes. While in bovine skin all TLRs apart from TLR6 were detected. The most abundant TLR transcripts within the ovine jejunum were TLRs 3, 5 and 6, while TLRs 6, 7 and 10 were abundant in both ovine Peyer's patch and mesenteric lymph node. In bovine skin TLRs 2 and 7 were most abundant. In all tissues tested TLR4 expression was at the lower limit of detection.