SteE Enhances the Virulence of Pullorum in Chickens by Regulating the Inflammation Response.

serovar Pullorum (. Pullorum) is a host-specific pathogen, which causes acute gastroenteritis with high mortality in poultry. However, the association between , encoded by type III secretion system 2, and virulence is not well-understood. To elucidate the functions of in . Pullorum, Δ strain was constructed using the λ-Red recombination technology. Compared to that in the wild-type, the deletion of in . Pullorum reduced bacterial invasion, proliferation, and late apoptosis in the infected HD-11 cells. In addition, we analyzed the mRNA expression levels of effector genes and cytokines by qRT-PCR. was associated with the regulation of various effector genes and inflammatory cytokines in HD-11 cells during . Pullorum infection. The wild-type effector promoted the expression of anti-inflammatory cytokines (IL-4 and IL-10) and reduced that of pro-inflammatory cytokines (IL-1β, IL-6, and IL-12) compared to that in the Δ-infected HD-11 cells and chicken spleens. Results from the chicken infection model showed that the deletion of resulted in significantly decreased colonization and long-term survival of the bacteria and alleviated pathological lesions compared to those in the wild-type. Further, increased the virulence of . Pullorum in chickens by regulating the expression of inflammatory cytokines. Our findings provide insights into the persistent infection and autoimmunity associated with in . Pullorum.