Toll-like receptor and antimicrobial peptide expression in the bovine endometrium

Darren Davies,Cliona O'Farrelly,P David Eckersall,R Steven Conlan,Shan Herath,Deyarina Gonzalez,I Martin Sheldon,Kieran G Meade,John O White

doi:10.1186/1477-7827-6-53

Abstract

BackgroundThe endometrium is commonly infected with bacteria leading to severe disease of the uterus in cattle and humans. The endometrial epithelium is the first line of defence for this mucosal surface against bacteria and Toll-like receptors (TLRs) are a critical component of the innate immune system for detection of pathogen associated molecular patterns (PAMPs). Antimicrobial peptides, acute phase proteins and Mucin-1 (MUC-1) also provide non-specific defences against microbes on mucosal surfaces. The present study examined the expression of innate immune defences in the bovine endometrium and tested the hypothesis that endometrial epithelial cells express functional receptors of the TLR family and the non-specific effector molecules for defence against bacteria.MethodsBovine endometrial tissue and purified populations of primary epithelial and stromal cells were examined using RT-PCR for gene expression of TLRs, antimicrobial peptides and MUC-1. Functional responses were tested by evaluating the secretion of prostaglandin E2 and acute phase proteins when cells were treated with bacterial PAMPs such as bacterial lipopolysaccharide (LPS) and lipoproteins.ResultsThe endometrium expressed TLRs 1 to 10, whilst purified populations of epithelial cells expressed TLRs 1 to 7 and 9, and stromal cells expressed TLRs 1 to 4, 6, 7, 9 and 10. The TLRs appear to be functional as epithelial cells secreted prostaglandin E2 in response to bacterial PAMPs. In addition, the epithelial cells expressed antimicrobial peptides, such as Tracheal and Lingual Antimicrobial Peptides (TAP and LAP) and MUC-1, which were upregulated when the cells were treated with LPS. However, the epithelial cells did not express appreciable amounts of the acute phase proteins haptoglobin or serum amyloid A.ConclusionEpithelial cells have an essential role in the orchestration of innate immune defence of the bovine endometrium and are likely to be the key to prevention of endometrial infection with bacteria.

Highlights

The endometrium is commonly infected with bacteria leading to severe disease of the uterus in cattle and humans
Endometrium contains endothelial, immune and blood cells, so the expression of Toll-like receptors (TLRs) was examined in purified populations of epithelial and stromal cells, which were free of immune cell contamination as determined by the absence of mRNA for the pan-leukocyte marker CD45 [14]
The secretion of prostaglandin E2 was maximal for the O55:B5 LPS and this was greater than O111:B4 LPS (P < 0.05), so subsequent experiments used O55:B5 E. coli LPS as the standard pathogen associated molecular patterns (PAMPs) to challenge cells

Summary

Introduction

The endometrium is commonly infected with bacteria leading to severe disease of the uterus in cattle and humans. The endometrial epithelium is the first line of defence for this mucosal surface against bacteria and Toll-like receptors (TLRs) are a critical component of the innate immune system for detection of pathogen associated molecular patterns (PAMPs). The present study examined the expression of innate immune defences in the bovine endometrium and tested the hypothesis that endometrial epithelial cells express functional receptors of the TLR family and the non-specific effector molecules for defence against bacteria. Bos taurus is a biologically relevant model to study female genital tract disease because infections are ubiquitous after parturition, often leading to uterine disease. The initial defence of the endometrium against microbes is dependent on innate immune systems, including Toll-like receptors (TLRs), antimicrobial peptides (AMPs), and acute phase proteins (APPs) [7,8]. Bos taurus endometrium presents an advantage over human or mouse models for studying innate immunity because it is possible to obtain purified populations of epithelial or stromal cells that are not contaminated by other immune cells [10]

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