Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2000
Publication Date: N/A
Interpretive Summary: Coccidiosis is a major parasitic disease of poultry which costs a significant economic loss to the poultry industry worldwide. The ability to develop a vaccine for coccidiosis would significantly reduce production losses due to this parasite and enhance US economy. In this study, ARS scientists studied intestinal lymphocyte responses following coccidia infection to understand the nature of protective host immune response to this parasite. The results showed that coccidia infection induces changes in the percentages of thymus-derived lymphocytes in the intestine. There was a significant increase of interferon-gamma production and CD4 cells at the time of parasite reduction indicating that these types of host immune responses are important in the elimination of coccidia parasites. These results also indicate the importance of studying intestinal responses to understand host immunity to coccidiosis. This study provides information on the nature of host protective immunity to avian coccidiosis and will enhance the possibility of developing immunological control strategy against this infection.
Kinetic differences between systemic vs. intestinal and humoral vs. cellular immune responses were elucidated in chickens experimentally infected with Eimeria maxima by comparing IFN-gamma and parasite-specific antibody levels in the intestine and serum during the course of infection. The level of serum IFN-gamma correlated significantly with fecal oocyst shedding (r2 = 0.97) thereby establishing the importance of cell-mediated immunity in coccidia infection. Moreover, intestinal IFN-gamma levels increased sooner than those in sera (4 vs. 6 days post-infection) and both were observed prior to the appearance of parasite-specific antibodies (8 - 10 days post-infection), again indicating the importance of intestinal cellular immunity in coccidiosis. Although IgG, IgA and IgM immunoglobulin isotypes of the antigen-specific antibody response increased significantly in both the intestine and serum following E. maxima infection, intestinal IgA-specific antibodies showed the most dramatic increase. However, the relevance of this observation in the context of primary Eimeria infection is unclear since the coccidia parasites have reached the final stages of their life cycle by this time. These results thus demonstrate the importance of T cell immune responses against coccidia, characterized by local IFN-gamma secretion in the intestine, in controlling parasite infection.