Dynamics of the avian inflammatory response to Salmonella following administration of the Toll-like receptor 5 agonist flagellin.

Previous work has shown that flagellin (FGN) is a potent stimulator in vitro of phagocytic cell functions of chickens. The purpose of this study was to define the effects of FGN on the inflammatory response to Salmonella enteritidis (SE) in chickens. Intra-abdominal (IA) FGN administration caused significant increases in peripheral blood leukocytes (PBL) compared with SE-injected controls at 4 and 8 h postinjection (P<or=0.05). The heterophil (PMN) was the predominant cell responsible for the increased numbers of leukocytes in the peripheral blood. In the abdominal cavity, leukocyte infiltrates were significantly greater in FGN-injected (8 h) and SE/FGN-injected (4 and 24 h) birds than in the SE-injected control birds. Again, the predominant leukocyte infiltrating the abdominal cavity was the PMN. Bovine serum albumin (BSA)-injected protein control birds showed no increases in PBL or in abdominal cell leukocyte infiltrates over saline-injected controls. In IA challenge studies, FGN reduced SE-associated mortality (26%) compared with mortality of 51% in the SE group (P<or=0.05). BSA-injected/SE-challenged chicks had mortality similar to that of the SE group. The data suggest that FGN is a potent stimulator of a heterophil-mediated innate immune response in vivo, protecting against bacterial infections in chickens.