Impact of IL-4–Expressing Transgenic Eimeria mitis on Reproductive Performance and Parasite Fecundity

It is crucial to understand the effects of genetic modification on the reproductive biology of species of Eimeria to determine their utility as vectors of live vaccines. This research involved a transgenic Eimeria mitis parasite that had been engineered to produce the gene chicken interleukin-4 (IL-4) via the assessment of its reproduction ability against the wild-type parasite. After the successful establishment of the IL-4 expressing IL-4 line, patterns of oocyst shedding, the periods of maximum shedding, the total reproductive output, and the sporulation phenotypes were studied under regulated experimental conditions. There was a strong decrease in fecundity in the transgenic E. mitis, relative to the wild-type strain. In several experiments the overall oocyst production by the IL-4 expressing line was less by approximately six-fold, and the maximum shedding time was 22-24 hours later than in birds infected with the wild type parasite. Despite the similarity in general morphology and sporulation capacity between the groups, the transgenic line produced significantly fewer oocysts per shedding interval and had a substantially lower cumulative reproductive output. The results indicate that the expression of IL-4 can alter the reproduction of E. mitis by making it a safer and less fecund parasite, which does not stop its functionality to complete the life cycle, though. This weakened phenotype increases the possibility of IL-4 expressing transgenic E. mitis as a live vaccine carrier, both of limited environmental contamination and specific immunomodulatory effects.