Abstract
Uterine infection and endometritis cause infertility and economic losses in the cattle industry. The innate immune response of the endometrium is critical in the elimination of pathogenic organisms that invade the uterus in postpartum cows. This study investigated the response of bovine endometrium to synthetic intracellular ligands which activate innate immunity by stimulating similar receptors to those used to recognise the presence of some viruses. Mixed primary epithelial and stromal cell cultures were treated with 5 μg/ml of CL097 (a TLR7/8 ligand) or 2 μg/ml of poly(dA:dT) (a DNA analogue) for either 6 h or 24 h. Cellular responses were assessed by the mRNA expression of 18 immune-related genes and 3 endogenous reference genes by conventional PCR followed by qRT-PCR from four replicate experiments. Bovine endometrial cells expressed the cytosolic pattern recognition receptors (PRRs) DDX58 (RIG-I), IFIH1 (MDA5) and LRRFIP1 which act as intracellular nucleic acid sensors. Neither ligand altered the expression of the extra-cytosolic pattern recognition receptors (PRRs) TLR3, TLR4, TLR7 or TLR8 whereas poly(dA:dT) treatment increased the expression of IFIH1 and DDX58. Treated cells also responded to CL097 or poly(dA:dT) with a differential up-regulation of genes involved in innate immune response including type I interferon/antiviral response (MX1, IFNAR1), antimicrobial activity (MUC1, SLPI) and cytokine activity (TNF, IL1B, IL8). Bovine endometrial cells therefore express both cytosolic and extra-cytosolic intracellular PRRs and are able to mount an innate immune response upon stimulation with intracellular ligands. This suggests an important role for these cells in the defence against viruses that may be present in the uterus in postpartum cows.
Highlights
Uterine infection and endometritis cause infertility and economic losses in the cattle industry
This study investigated the response of bovine endometrium to synthetic intracellular ligands which activate innate immunity by stimulating similar receptors to those used to recognise the presence of some viruses
Bovine endometrial cells expressed the cytosolic pattern recognition receptors (PRRs) DDX58 (RIG-I), IFIH1 (MDA5) and LRRFIP1 which act as intracellular nucleic acid sensors
Summary
Uterine infection and endometritis cause infertility and economic losses in the cattle industry. Specialised immune cells including macrophages, neutrophils and dendritic cells (DCs) possess pattern recognition receptors (PRRs) such as toll-like receptors (TLRs), nucleotide oligomerisation domain (NOD)-like receptors (NLRs), retinoic acid inducible gene I (RIG-I)-like receptors (RLRs) and cytosolic DNA sensors (CDS). These PRRs have an important role in recognising pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS) and nucleic acids (RNA and DNA) from bacterial and viral pathogens, leading to the activation of an innate immune response [5] [6]. Viral RNA or DNA are either recognised outside the cytoplasm of infected cells by TLRs located in intracellular compartments such as endosomes and endolysosomes, or within the cytoplasm by several DNA sensors and the RLRs such as DExD/H-box helicase 58 (DDX58, known as RIG-I) and interferon induced with helicase C domain 1 (IFIH1, known as MDA5) [6] [7]
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