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.
*Presenting author
#Corresponding author: hlilleho@anri.barc.usda.gov