A DNA vaccine encoding a conserved Eimeria protein induces protective immunity against live Eimeria acervulina challenge

Coccidiosis is caused by several distinct intestinal protozoa of Eimeria sp ., and is responsible for intestinal lesions and severe body weight loss in chickens. To develop a DNA vaccination strategy for coccidiosis, an expres sion vector pMP13 encoding a conserved antigen of Eimeria was constructed b y subcloning 3-1E cDNA into pBK-CMV and used to elicit protective immunity against E. acervulina. One-day-old chickens were immunized intramuscularly (IM) or subcutaneously (SC) with various doses of pMP13 expression vector r anging from 5 to 100 ug two weeks apart and were challenged with 5 x 10(3) E. acervulina. Chickens immunized with 5, 10, 50 or 100 ug of pMP13 plasmid , but not control plasmid, pBK-CMV, showed significantly reduced oocysts fo llowing challenge infection with E. acervulina. Two injections were in gene ral more effective than one injection with higher dose of DNA eliciting bet ter protection. At 10 days post challenge infection, maximum levels of circ ulating antibodies were detected regardless of the routes of injection, alt hough IM injection provided higher levels of serum antibodies compared to S C injection. Serum antibody levels demonstrated a dose-dependent response s howing higher antibody production at higher DNA dose. DNA immunization with pMP13 also induced significant changes in T-cell subpopulations in the spl een and duodenum intraepithelial lymphocytes. At 4 days post DNA immunizati on, pMP13-immunized chickens showed lower CD8, and higher CD4(+) and gamma delta T+ cells in the duodenum compared to the pBK-CMV-immunized chickens. Following challenge infection with E. acervulina, pMP13-immunized chickens showed lower CD8(+) and alpha beta T+ cells, and higher CD4(+) cells than p BK-CMV-immunized chickens in the duodenum. These findings demonstrate that DNA immunization with pMP13 induce Local and systemic host immune responses against Eimeria. Published by Elsevier Science Ltd.