Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: June 12, 2006
Publication Date: September 9, 2006
Citation: Genovese, K.J., He, H., Kogut, M.H. 2006. In vivo effects of Salmonella flagellin administration to day-old chickens [abstract]. American Society for Microbiology. p. 43. Technical Abstract: Flagellin is a highly evolutionarily conserved bacterial product that has been shown to be recognized by the innate immune system through toll-like receptor (TLR) 5. Previous work has shown that flagellin is a potent stimulator of in vitro phagocytic cell functions of chickens. The purpose of the present studies was to define the effects of flagellin administration to chickens in vivo. Day-old chicks were administered, by intra-abdominal injection, either 2.0 ug flagellin in sterile saline/bird or sterile saline alone. 1 hr after flagellin administration, chicks were challenged by intra-abdominal injection with Salmonella enteritidis [5 x 10**3 colony forming units (CFUs)/bird]. Peripheral blood samples and abdominal leukocyte infiltrates were monitored at 0, 4, 8, and 24 hr post-infection. Chick mortality was recorded over a 72 hour period. Flagellin administration was found to protect chicks from SE– associated mortality, reducing mortality by 50% as compared to the SE infected control group. At 4 hours post-infection, total white blood cells (WBCs) in the peripheral blood showed a significant increase in flagellin, flagellin + SE, and SE alone groups as compared to control birds. At 4, 8, and 24 hr post-infection, chicks in both the flagellin alone and the SE + flagellin groups had significantly higher total WBCs than the SE alone control group. The largest portion of the increase in peripheral blood WBCs was due to a significant increase in heterophils in the SE, SE + flagellin, and flagellin groups, with the flagellin and SE + flagellin groups having a significantly greater increase in the numbers of heterophils in the peripheral blood. Total leukocyte numbers in the abdominal cavity of birds in the flagellin alone group were significantly greater than in the SE alone and SE + flagellin groups at 4 and 8 hours post-injection, then were on the decline by 24 hours post-injection. In the SE + flagellin group, abdominal total leukocytes increased overall, with a slight decrease in numbers at 8 hours post-injection, but were significantly greater than the SE alone group at 4 and 24 hr post-injection. Leukocytes in the abdomen of birds in the SE alone group steadily increased over the 24 hour period. The predominant cell type associated with increasing numbers of leukocytes in the abdominal cavity was the heterophil, with the flagellin and SE + flagellin groups having significantly greater numbers of heterophils in the abdominal cavity than did birds in the SE alone group. The data suggest that the TLR 5 agonist, flagellin, is also a potent stimulator of a heterophil-mediated innate immune response in vivo, with subsequent protective effects on bacterial infections in the chicken and may have applications as an adjuvant in vaccines or as a general prophylactic innate immune enhancing agent in poultry during the first week post-hatch.