A SYSTEMS BIOLOGY APPROACH TO UNDERSTANDING THE SALMONELLA-HOST INTERACTOME IN POULTRY AND SWINE
Location: Food and Feed Safety Research
Title: Gene expression analysis of toll-like receptor pathways in heterophils from genetic chicken lines that differ in their susceptibility to Salmonella enteritidis
Submitted to: Frontiers in Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 14, 2012
Publication Date: July 4, 2012
Citation: Kogut, M.H., Chiang, H., Swaggerty, C.L., Pevzner, I.Y., Zhou, H. 2012. Gene expression analysis of toll-like receptor pathways in heterophils from genetic chicken lines that differ in their susceptibility to Salmonella enteritidis. Frontiers in Genetics. 3:1-10.
Interpretive Summary: During the first week of life after hatching, the baby chick must fight off bacterial infections such as Salmonella. We do not know how the chicks are able to see the bacteria and start their immune system to fight these germs. The objective of this experiment was to look at a specific white blood cell of the chicken called the heterophil and determine how the cells recognize bacteria and start their immune system. We found the heterophils have chemical structures on their surfaces that feel the presence of bacteria. Once they know the bacteria are present, the cells produce a series chemical that tell their immune system that the bacteria are there and help is needed. The results of this experiment are important to the pharmaceutical industry in the United States because we now know which chemicals are produced (or not) by the baby chick’s cells of the immune system when they see Salmonella. Thus, we can now see if there are ways for us to get the baby chick to make these chemicals which will help the chick fight Salmonella infections.
Previously conducted studies using two chicken lines (A and B) show that line A birds have increased resistance to a number of bacterial and protozoan challenges and that heterophils isolated from line A birds are functionally more responsive. Furthermore, when stimulated with toll-like receptor (TLR) agonists, heterophils from line A expressed a totally different cytokine and chemokine mRNA expression pattern than heterophils from line B. A large-scale gene expression profile using an Agilent 44K microarray on heterophils isolated from line A and line B also revealed significantly differential expression in many immune-related genes following Salmonella enteritidis (SE) stimulation, which included genes involved in the TLR pathway. Therefore, we hypothesize the differences between the lines result from distinctive TLR pathway signaling cascades that mediate heterophil function and thus innate immune responsiveness to SE. Using quantitative RT-PCR on mRNA from heterophils isolated from control and SE-stimulated heterophils of each line, we profiled the expression of all chicken homologous genes identified in a reference TLR pathway. Several differentially expressed genes found were involved in the TLR-induced My88-dependent pathway, showing higher gene expression in line A than line B heterophils following SE stimulation. These genes included the toll-like receptor genes TLR4, TLR15, TLR21, MD2, the adaptor proteins toll-interleukin 1 receptor domain containing adaptor protein (TIRAP), tumor necrosis factor-receptor associated factor 3 (TRAF3), the I'B kinases TGF-ß-activating kinase 1 (TAK1), IKKe and IKKa, the transcription factors NFkB2 and interferon regulatory factor 7 (IRF7), phosphoinositol-3 kinase (PI-3K), and the mitogen-activated protein kinase (MAPK) p38. These results indicate that higher expression of TLR signaling activation of both MyD88-dependent and TRIF-dependent pathways are more beneficial to avian heterophil-mediated innate immunity, and a complicated regulation of down-stream adaptors is involved in stronger induction of a TLR-mediated innate response in the resistant line A. These findings identify new targets for genetic selection of chickens to increase resistance to bacterial infections.