Contribution of innate and adaptive immune cells to the elimination ofSalmonella entericaserotype Enteritidis infection in young broiler chickens
Authors: Meijerink Nathalie , van den Biggelaar Robin H.G.A. , van Haarlem Daphne A. , Stegeman J. Arjan , Rutten Victor P.M.G. , Jansen Christine A. 
Published: January 2021

Salmonella entericaserotype Enteritidis (SE) is a zoonotic pathogen which causes foodborne diseases in humans through contaminated poultry products, as well as severe disease symptoms in young chickens. More insight in innate and adaptive immune responses of chickens to SE infection is needed to understand elimination of SE. Seven-day-old broiler chickens were experimentally challenged with SE and numbers and responsiveness of innate immune cells including natural killer (NK) cells, macrophages and dendritic cells (DCs) were assessed during 21 days post-infection (dpi). In parallel, numbers and function of γδ T cells, CD8+and CD4+T cells as well as antibody titres were determined. SE was observed in the intestine and spleen of SE-infected chickens at 7 dpi. NK and T cells responded first to SE at 1 and 3 dpi as indicated by increased numbers of intestinal IL-2Rα+and 20E5+NK cells, in addition to enhanced activation of intestinal and splenic NK cells. At 7 dpi in the spleen, the presence of macrophages and the expression of activation markers on DCs was increased. At 21 dpi, an increase in intestinal γδ and CD8+T cell numbers was observed. Furthermore, SE-specific proliferation of splenic CD4+and CD8+T cells was observed and SE-specific antibodies were detected in all blood samples of SE-infected chickens. In conclusion, SE results in enhanced numbers and activation of innate cells during early stages of infection and it is hypothesized that in concert with subsequent specific T cell and antibody responses, reduction of SE in infected chickens is achieved. A better understanding of innate and adaptive immune responses important in the elimination of SE will aid in developing immune-modulation strategies, which may increase resistance and prevent SE infection and colonization in young broiler chickens and hence increase food safety for humans.

Author summary

Salmonella entericaserotype Enteritidis (SE) causes foodborne zoonotic diseases in humans, as well as a severe disease in young chickens. As a consequence of which health and welfare of humans and chickens are affected, resulting in substantial economic losses. To enable development of immune-mediated prevention strategies in chickens, more insight in the immune responses to SE is needed to understand how the infection is eliminated. For this purpose, we investigated non-specific and specific immune responses upon experimental SE infection in young broiler chickens. In this study, we found SE in the intestine and spleen of SE-infected chickens at 7 days post-infection (dpi). We show that natural killer (NK) cells respond first by enhanced presence and activation, followed by increased presence of macrophages and activation of dendritic cells. These early responses are hypothesized to stimulate the observed subsequent specific T cell and antibody responses. Better understanding of immune responses important in the elimination of SE will aid in developing immune-modulation strategies, which may increase resistance and prevent SE infection and colonization in young chickens and hence reduce SE-related foodborne illness in humans.