Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2008
Publication Date: December 1, 2008
Citation: Konjufca, V., Jenkins, M.C., Wang, S., Juarez-Rodrigues, M.D., Curtiss, R. 2008. Immunogenicity of recombinant attenuated Salmonella enterica serovar Typhimurium vaccine strains carrying a gene that encodes Eimeria tenella antigen S07. Infection and Immunity. 76:5745-5763.
Interpretive Summary: Avian coccidiosis is an intestinal disease of broilers caused by protozoa in the genus Eimeria. The disease is prevalent world-wide, and causes an annual loss of over $ 350 million to the U.S. poultry industry because of weight loss and poor feed utilization in infected chickens. The disease has been controlled for decades by anticoccidial medication of feed with ionophore drugs or synthetic chemicals. In recent years, the use of coccidiosis vaccines based on low doses of live Eimeria oocysts have gained popularity in controlling this protozoan disease because of parasite drug resistance and increased consumer emphasis on drug-free broilers. Although live oocyst vaccines are effective, they are somewhat expensive to produce and require the absence of anti-coccidial drugs during grow-out. A subunit vaccine based on one to several proteins of Eimeria is an ideal, yet presently unavailable approach to vaccination. The purpose of the present study was to test the expression and immunogenicity of an Eimeria antigen, termed S07, in a harmless Salmonella vector. It was found that Salmonella can express Eimeria S07 antigen in a variety of vectors, colonize intestinal tissue and induce an immune response in inoculated chickens. Tissue colonization and humoral immune responses were dependent on Salmonella plasmid vector used in primary and booster immunization. These findings indicate that recombinant Eimeria antigen can be delivered to the chicken immune system, which may induce protective immunity against coccidiosis infection.
In an attempt to develop an efficacious vaccine against avian coccidiosis, research was conducted using Type III Secretion System (TTSS) of Salmonella to deliver Eimeria antigens into the cytoplasm of host cells. Once delivered, recombinant protein may enter the MHC I antigen processing pathway for induction of antigen-specific CTL responses that would result in protection against this parasite. The Eimeria tenella gene encoding a sporozoite antigen SO7 antigen was fused to the 80 amino acid (aa) translocation domain of Salmonella enterica Serovar Typhimurium gene sopE in the parental pYA3868 and pYA3870 vectors to generate pYA4156 and pYA4157,and was found to be secreted by TTSS of Salmonella. Newly constructed TTSS vectors were introduced into the host strain '8879 ('phoP233 'sptP1033::xylE 'asdA16), an attenuated derivative of the highly virulent UK-1 strain. Vector pYA4184 was constructed for delivery of the SO7 via the Type II '-lactamase secretion system of Salmonella. However, SO7 protein was toxic to Salmonella when expressed at higher amounts; thus we placed the synthesis of this protein under control of the lacI repressor gene, whose expression in turn is dependent on the amount of available arabinose in the media. Vector pYA4184 was introduced into the host strain '9242 ('phoP233 'asdA16 'araBAD23 'relA198::araC PBAD lacI TT). In vivo studies reveal that the RASVs colonize the intestinal tract of one and two week-old chickens and induce strong antigen–specific antibody titers.