Adjuvant effect of Vernonia amygdalina leaf extract on host immune response to hepatitis B virus subunit vaccine.

Aim of the study: Adjuvants can increase the efficiency and reduce the number of required doses for hepatitis B vaccination. Thus the study was designed to investigate whether V. amygdalina leaf extract may be used as an adjuvant to the conventional hepatitis B surface antigen-based vaccine through humoral response analyses. Methodology: The toxicity/safety margin of V. amygdalina was determined using Lorke's method. Immunization was carried out in mice in two phases, phase 1 employed a 3-times vaccination schedule while phase 2 tested 2-times vaccination schedule. The humoral immune response was determined using ELISA test. The total white blood count, different white blood count, aspartate aminotransferase level, alanine aminotransferase level were determined and the body weight of the mice periodically monitored. Results: Our data show that V. amygdalina was not toxic up to the dose of 5000 mg/kg bodyweight (bw). At a concentration of 250 mg/kg bw as an adjuvant in a three times vaccination schedule, it increased IgM, IgG1 and IgA antibody responses. In a 2-times vaccination schedule, 1000 mg/kg of V. amygdalina as an adjuvant to hepatitis B vaccine was able to elicit effective antibody production (0.174±0.002) significantly (P <0.05) higher than the conventional hepatitis B vaccine group (0.109±0.002) which received 3-times vaccine dose. It equally enhanced innate cell-mediated immune response by increasing total white blood cell, neutrophil and lymphocyte counts. The adjuvant-vaccine combination did not produce side effects as the aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were within the normal ranges. The liver excised from the sacrificed mice at the end of the vaccination series showed no sign of congestion, inflammation or colour change. Periodic mice body weight monitoring showed similar growth pattern between the treatment and control groups. Conclusion: Results obtained suggest that V. amygdalina may serve as an effective adjuvant to hepatitis B virus vaccine.