Submitted to: Epidemiology and Infection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2004
Publication Date: 12/1/2004
Citation: Ferro, P.J., Swaggerty, C.L., Kaiser, P., Pevzner, I.Y., Kogut, M.H. 2004. Heterophils isolated from chickens resistant to extra-intestinal Salmonella enteritidis infection express higher levels of pro-inflammatory cytokine mRNA following infection than heterophils from susceptible chickens. Epidemiology and Infection. 132:1029-1037.
Interpretive Summary: The immune system of a baby chick during the first week of life is not very good at fighting bacterial infections such as Salmonella. There are cells in the blood of baby chicks that help fight infections called heterophils. Earlier studies in our laboratory have shown a difference between the ability of heterophils from four different groups of baby chicks to kill Salmonella. The purpose of the current study was to see if the baby chicks whose heterophils were better at killing bacteria were less likely to get sick when infected with Salmonella. In this study, we found that baby chicks whose heterophils killed more bacteria were less likely to get infected with Salmonella. We also found possible reasons for these differences by identifying cell related chemicals, called cytokines, were different between the baby chicks who got infected and those that didn't. These findings are important to commercial poultry breeders because baby chicks whose cells are better at fighting an infection are more likely to live longer, thus producing more eggs or going to market.
Technical Abstract: Previous studies in our laboratory have shown differences in in vitro heterophil function between two pure lines of broiler chicks and their F1 reciprocal crosses. The objectives of the current study were to 1) determine if the previously reported in vitro differences in heterophil function between the lines translated to an increase in in vivo resistance to extraintestinal infection with Salmonella enteritidis (SE) and 2) to quantitate pro-inflammatory cytokine mRNA expression levels in heterophils isolated from SE-infected chicks from different lines. Day-old chicks from four different lines (pure lines=A and B; line C = male B x female A; line D = male A x female B) were challenged orally with SE. Twenty-four hours post-challenge, livers and spleens were aseptically removed, incubated overnight in tetrathionate enrichment broth, plated and subsequently analyzed for the presence of non-lactose fermenting Salmonella colonies. The two lines reported to have more functionally efficient heterophils (A and D) were less susceptible to extraintestinal SE infections whereas the two lines reported to have functionally less efficient heterophils (B and C) were more susceptible to SE organ invasion. Four hours post-challenge peripheral blood heterophils were isolated from SE-infected and control chicks, total RNA extracted, and analyzed for pro-inflammatory cytokine (IL-1beta, IL-6, IL-8) expression using real-time quantitative RT-PCR. Pro-inflammatory cytokine mRNA expression was significantly up-regulated in heterophils isolated from chicks that were more resistant to SE organ invasion (A and D) when compared to expression in heterophils isolated from the more susceptible lines (B and C). To our knowledge, this is the first report to quantitate IL-1beta, IL-6, and IL-8 mRNA expression levels in heterophils isolated from day-old chicks orally challenged with SE. These results show a relationship between in vitro heterophil function and resistance to organ invasion by SE. These data also indicate that pro-inflammatory cytokine mRNA expression by heterophils contributes, in part, to resistance of day-old chicks to extraintestinal infection by SE.