Immunomodulatory Effects of IL-4–Expressing Eimeria mitis on Host Hematology and Systemic Immune Parameters in Chickens

Genetically modified Eimeria species expressing host cytokines represent a promising strategy for developing live vaccines with intrinsic immunomodulatory properties. In this study, the effects of infection with an interleukin-4 (IL-4)–expressing transgenic Eimeria mitis strain on host hematological and systemic immune parameters were evaluated and compared with those induced by wild-type E. mitis. Chickens were experimentally infected with either the transgenic or wild-type parasite, and blood samples were collected at defined time points post-infection to assess changes in red and white blood cell indices, hemoglobin concentration, packed cell volume, and leukocyte profiles. Infection with the IL-4–expressing E. mitis resulted in distinct hematological patterns compared with wild-type infection. Birds infected with the transgenic strain exhibited less pronounced reductions in red blood cell count, hemoglobin concentration, and packed cell volume, indicating reduced physiological stress and milder systemic impact. Additionally, alterations in total leukocyte counts and differential leukocyte populations suggested a modulation of immune responses associated with IL-4 expression. The observed hematological responses indicate that expression of IL-4 by transgenic E. mitis influences host systemic physiology beyond the intestinal site of infection. The combination of reduced parasite fecundity, attenuated pathology, and moderated hematological disturbance supports the concept that IL-4–expressing E. mitis functions as a biologically safer live parasite. These findings provide important evidence that cytokine-expressing Eimeria strains can modulate host immune and physiological responses, reinforcing their potential application as next-generation live vaccine vectors in poultry.