The interaction between egg yolk and Escherichia coli in disease pathogenesis during egg yolk peritonitis

Introduction. In the chicken, after misovulation of a yolk-filled follicle into the body cavity or during normal ovarian regression during molt, macrophages clear yolk lipid and transport it back to the liver for disposal in a process that appears to be similar to mammalian reverse cholesterol transport. In the presence of E. coli, yolk clearance fails and egg yolk peritonitis results. The objective of this research was to determine how egg yolk and E. coli interact to cause egg yolk peritonitis.;Overall conclusion. Egg yolk and E. coli interact to cause EYP. This interaction may be caused by the production of contradictory signal cascades within macrophages. In general, macrophages faced with bacterial infection become activated and initiate a robust inflammatory response to induce bacterial clearance. Macrophages faced with egg yolk do not become activated and instead efficiently clear yolk lipid without provoking and inflammatory response from the host. When both yolk and bacteria are present and intermediate response that is not effective at clearing a bacterial infection or removing excess lipid is induced leading to disease.;Results and conclusions. (1) Egg yolk altered the acute phase immune response to E. coli. Pro-inflammatory cytokine expression and blood heterophil levels were reduced, while plasma iron increased and plasma copper decreased. (2) Chicken macrophages grown in the presence of egg yolk and LPS expressed lower levels of pro-inflammatory cytokines (IL-1, IL-8, IFNgamma) and produced less nitric oxide than macrophages grown in the presence of only LPS. However, the expression of anti-inflammatory IL-10 remained unchanged. (3) Three-week old chickens were injected in the wing-web with PBS-control, egg yolk, LPS or egg yolk and LPS. Histopathological examination of the wig-webs revealed that egg yolk caused the local inflammatory response to LPS to be more mononuclear and less suppurative in nature although the magnitude of the cellular response appeared to be unchanged. (4) LPS prevented transport of egg yolk through the bloodstream. (5) LPS probably prevents yolk clearance by inhibiting lipid flux through macrophages.