:: The IXth International Coccidiosis Conference ::

Contributed Papers: Oral Presentations
Vaccines

In Ovo and Dietary Modulation of Host Intestinal Immunity and its Subsequent Effects on Coccidiosis

Rami A. Dalloul,1,2,* Hyun S. Lillehoj1,# and John A. Doerr2
1Animal Parasitic Diseases Laboratory, Animal and Natural Resources Institute, USDA-ARS, Beltsville, MD 20705, USA
2College of Agriculture and Natural Resources, University of Maryland, College Park, MD 20742, USA

ABSTRACT
Various agents of known influence on the mucosal immune system were evaluated as immunomodulators in poultry in response to coccidial infections. These included vitamin A, probiotics, and synthetic CpG oligodeoxynucleotides (ODNs). Vitamin A deficiency impaired the gut immune defenses of broiler chickens, which are best characterized by alteration in intraepithelial lymphocyte (IEL) subpopulations, mainly CD4+ T cells, resulting in increased susceptibility to coccidiosis. Conversely, supplementing broiler diets with a Lactobacillus-based probiotic stimulated the local immune system and improved resistance to Eimeria, as shown in a 4-fold reduction in oocyst shedding. Further investigation on the probiotic effects demonstrated that probiotic-fed chickens shed fewer oocysts than chickens without probiotic even in vitamin A-deficient birds, thus confirming improved resistance to coccidiosis. Studies with other immunoprotective agents involved in vitro, in vivo, and in ovo testing of a number of CpG ODNs. Several CpG ODNs including D19 and 2006 induced strong IL-6 and nitric oxide secretion by HD11 cells. Intracellular killing of Salmonella enteritidis was also increased in ODN 2006-activated HD11 cells. Also, in vivo CpG treatment with ODN 2006 enhanced birds’ resistance to coccidiosis in a normally susceptible chicken strain (TK), as shown by reduced oocyst shedding and improved weight gain during E. acervulina infection. Further, in ovo vaccination with CpG ODNs and an Eimeria recombinant microneme protein (MIC2), alone or in combination, showed positive effects on susceptibility to coccidiosis. In ovo injection of ODNs D19 and 2006 alone reduced oocyst shedding, but did not affect weight gain during E. acervulina infection. When co-administered with MIC2, both ODNs reduced oocyst shedding; however, only ODN D19 plus MIC2 consistently improved weight gain. Also, vaccinating with ODN 2006 or MIC2 protein curtailed oocyst shedding, but did not enhance weight gain in E. tenella-infected birds. Collectively, these agents demonstrated immunoenhancing and adjuvant effects during Eimeria infections. However, regulation of immune responses is extremely complex and complete knowledge of how the immune system responds to Eimeria infections requires more research.