Pathological Study On Immunoprotective Mechanism Of E.acervulina Immune-enhancing DNA Vaccine

Chicken coccidiosis is the major parasitic disease, which is caused by Eimeria parasitizing the intestine of chicken. So far, the preventive method of this disease is application of chemicals. However, drug resistance to coccidia restrained the effectiveness of their utilization, and outbreak of coccidiosis often appeared and caused serious economic loss in poultry industry. Recently, vaccine becomed a main method to prevent coccidiosis. The development of coccidiosis vaccine by genetic engineering technique, such as the DNA vaccine, gets more and more important. This study was carried out to study the pathological changes of immunoprotective mechanism of utilization of immune-enhancing DNA vaccine of E. acervulina in chicken. The experiment contents and results were as follows:1. With routine pathological methods, the pathological changes of chickens infected with E. acervulina oocyst were observed. Chickens infected with E. acervlina sporulated oocysts showed depression, loss of appetite and not likely to drink, discharge of white mucuous feces. Under the microscope, small intestine appeared hyperemia, the epithelial cells showed degeneration and necrosis. At different times, there are different stages of parasite could be observed in the intestinal cells.2. Using immunoperoxidase staining, the attacking path and infected location of E. acervulina were studied. The results showed E. acervulina entered small intestine epithelial cells at the beginning, and then got into the intestinal gland cells in the submucuous layer. After development and multiplication, infected and dispersed into the total area of the intestinal villi.3. The four kinds of eukaryotic recombinant expression plasmids of E. acervulina DNA vaccine was constructed, and were used respectively to immunize SPF chickens at 14-day-old with 100μg of plasmid by injection intramuscularly into thigh muscle. Immunization was boosted at 21-day-old. Chickens in each group were challenged with 5×104 E. acervulina sporulated oocysts at 28-day-old The pathological changes of experimental chickens at different times were observed. The results showed that, in the non-immunized but infected group chickens (group H), spleenic and thymic lymphocyte arranged losely and lymphocyte number decreased, small intestine injured seriously, epithelial cells degenerated and necroses, intestinal villi broken with obvious haemorrhage. however, in the group of 3-1E-IL-15 (group S), 3-1E+cIL-15 (group C), 3-1E+NIL-15 (group N), 3-1E (group E), spleenic and thymic lymphocyte increased with closely arrangement, the pathological changes of intestine decreased in degree and kept its entire structure. Furthermore, the number of parasite in different stages decreased. The results demonstrated that the utilization of four kinds of DNA vaccine (groups S,C,N,E) could provided certain degrees of protection against E. acervulina challenge.