Effect of alum co-adjuvantation of oil adjuvant vaccine on emulsion stability and immune responses against haemorhagic septicaemia in mice

Haemorrhagic septicaemia (HS), caused by Pasteurella multocida, is the most important bacterial disease of cattle and buffaloes in India. Oil adjuvant vaccine (OAV) is the most potent vaccine available for the control of HS. The study aims to evaluate the effect of alum co-adjuvantation of OAV on emulsion stability and immune response. Two different oil adjuvant vaccines viz., standard oil adjuvant vaccine (OAV) and alum precipitated oil adjuvant vaccine (A–OAV) were prepared with Pasteurella multocida antigen. Emulsion stability was tested by centrifugation, storage at 37 oC for 3 months and microscopy. Immune responses were evaluated by ELISA antibody titer, CD4, CD8 T cell populations and survival post challenge by P. multocida in mice. The separation of aqueous and oil phase of emulsion by centrifugation and storage test were 0 and 6.76% in A-OAV as compared to 11.00 and 26.39% in OAV, respectively. The mean droplet size was significantly smaller (p<0.01) in A–OAV as compared to OAV. The A–OAV recorded higher ELISA antibody titer (p<0.05) up to 21st days post vaccination, and higher CD4 (p>0.05) and CD8 T cell (p<0.05) populations compared to OAV. The A–OAV group conferred 100% protection after challenge with both 100 LD50 and 1000 LD50 as compared to 100 and 60% respective protection by OAV group. The results indicates that A–OAV had better emulsion stability, produces higher level of CD4, CD8 T cells and antibody titer with better protection compared to oil adjuvant vaccine.