Protective Immunity and Vaccine Potential of IL-4–Expressing Eimeria mitis Against Homologous Challenge in Chickens

Live Eimeria-based vaccines are still considered one of the best methods of managing avian coccidiosis, but the safety, pathogenicity, and environmental pollution have restricted their wider use. Modification of Eimeria species to express host cytokines is a new method of enhancing the effectiveness of a vaccine and minimizing biological risk. The protective immunity and vaccine potential of an interleukin-4 (IL-4)-expressing transgenic Eimeria mitis (E. mitis) strain in chicken were assessed in this research against homologous challenge. The IL-4 expressing E. mitis strain was immunized in chickens and later challenged by the wild-type E. mitis. Protective efficacy was determined through observing the oocyst shedding, clinical signs, and host performance indicators after the challenge. The transgenic strain immunized birds showed a significant decrease in oocyst production at the time of challenge as compared to non-immunized controls, which showed a positive result that the immunization induced successful protective immunity. Besides, there were milder clinical outcomes and more stable physiological parameters of immunized birds, which is consistent with improved immune response. The IL-4 E. mitis strain showed a beneficial ratio between attenuation and immunogenicity. There was less fecundity and slower shedding, which minimized environmental contamination, and the growth of parasites was a guarantee of strong immune stimulation. The findings demonstrate that IL-4 gene expression improves the vaccine capacity of E. mitis through protective immunity with reduced host pathology.