Abstract: Objective To investigate the impact of 4-phenylimidazole(4-PI) combining with aluminum hydroxide as an immunological adjuvant on humoral immune response in mice immunized with live hepatitis A virus (HAV) attenuated live vaccine (HepA-1). Methods Seven experiment groups are set up, with 7 ICR mice per group randomly. Use 1×phosphate buffer saline as negative control group, aluminum adjuvant group (HepA-1 200 μL+Al(OH)₃ 24 μL), antigen group (HepA-1), M4 (HepA-1+4-PI 1 mg) as control, in which mice were injected subcutaneously with 300 μL, immunizing one time. The mice of three groups (M1, M2, M3) were immunized with live hepatitis A vaccine HepA-1 mixed with aluminum hydroxide,4-PI at concentrations of 500 μg, 1 mg, 1.5 mg respectively. The anti-HAV specific IgG antibody levels were tested by indirect ELISA method in the serum of mice after the first 4th, 8th, 12th,16th week of injection. The health condition of mice were observed and record during the whole study. Results HAV-specific IgG levels of all mice were detected at four setting time point except negative control group and reached the maximum at 12th week. The IgG titers of group M2 mice were the highest at all detected time point and showed significant difference with those of antigen group (t=4.449, 3.633, 2.565, 6.809; P<0.05), group M4 (t=6.256,4.796, 4.153, 4.113; P<0.05) and aluminum group at 4th week (t=2.877, P<0.05). The IgGs induced by group M4 was comparable to the antigen group in each test phase. The optimal dosage of 4-PI was 1 mg for each mouse. The physiological indexes in all the groups of mice was normal during the course of experiment. Conclusions The humoral immune responses induced by HepA-l in mice was heightened by 4-PI combined with aluminum hydroxide,which had potential for developing a novel and compound HepA-1 adjuvant.

Key words: 4-Phenylimidazole(4-PI), Aluminum hydroxide, Adjuvant, Hepatitis A virus attenuated live vaccine (HepA-1), Humoral immune