Protective effect of ClpP fusion protein against invasive infection of different serotype Streptococcus pneumoniae in routine models
Objective To evaluate the protective effects elicited by ClpP fusion protein in animal protection tests. Methods Pneumococcal antigens were purified from recombinant Escherichia coli express-ing CIpP cloned gene. 6- to 8-week-old female BALB/c mice were immunized intraperitoneally with either ClpP or PBS plus alum. Every mouse received three doses of 20 μg antigen or PBS in 100 mg of alum adju-vant at 14 d intervals. Sera were collected from mice and analyzed by ELISA 1 week after the third immuni-zation, Intraperitoneal-challenge experiments with 12 different serotypes of Streptococcus pneumoniae were carried out 2 weeks after the third immunization, and we compared their median survival times and survival rates respectively by Mann Whitney U test and Fisher exact test. Results ELISA analysis demonstrated high titer specific antibody responses to ClpP. The median survival times for mice immunized with ClpP pro-tein antigens in adjuvant were significantly longer than those for mice that received the adjuvants alone. Con-clusion A highly expressed recombinant ClpP protein has been successfully obtained and proved to exert the protection against invasive pneumococcal infection without relation of serotype, suggesting ClpP can be a promising candidate vaccine. 
 
Key words: 
Streptococcus pneumoniae;  Vaccine;  ClpP fusion protein