The immunomodulatory effect of CpG motifs-rich plasmids on immunity developed against Salmonella enterica serovar Enteritidis vaccine in chickens

Abstract

In the present study the dose-dependent immunomodulatory effect of CpG ODN on Salmonella Enteritidis bacterin in broiler chickens was investigated by recording the intestinal colonization, cellular responses, mucosal and systemic immune responses of challenged chicks. A total of 200 one-day-old broiler chicks, divided into 5 groups, were used in this study, 40 chicks per group. Three groups were immunized with Salmonella Enteritidis bacterin adjuvanted with different doses of CpG ODN (50µg, 100µg and 200µg). Two control groups included a group that was immunized with Salmonella Enteritidis bacterin adjuvanted with aluminum hydroxide(40 one-day-old broiler chicks) and a non-immunized group (40 one-day-old broiler chicks) . The intestinal colonization, cellular responses, mucosal and systemic immune responses of immunized chickens was measured at different intervals, until 42 days of age. Two weeks post-immunization, 20 chicks from each group were orally challenged by Salmonella Enteritidis fresh bacterial culture (1.2x108 CFU/ml). The survival rates and the pathological changes of challenged chickens in the different groups were monitored for extra 10 days post challenge. Compared to the aluminum hydroxide adjuvanted bacterin the CpG-ODN adjuvant bacterin induced significant protection and improved survival rate of challenged chickens. Also Salmonella Enteritidis was not recovered from the intestinal tract of vaccinated challenged groups. There was a significant dose-dependent immunostimulatory effect of CPG-ODN on the level of secretory IgA and the induced mucosal responses. The chicken group that received 200-CpG ODN showed the highest IgA response followed by 100-CpG ODN group then the 50-CpG ODN and the aluminum hydroxide groups (P < 0.05). Also, cellular interactions were remarkably reduced in the liver and intestine of CpG ODN-treated chickens. No inflammatory cellular infiltrations were seen in the liver and intestine of 200-CpG ODN treated chickens.