The potential of exopolysaccharides (EPS) extracted from Chlorella sp. as adjuvant for formalin-killed whole organism of Mannheimia haemolytica A2 (MhA2) vaccine was investigated. Chlorella sp. was cultured in F/2 media and EPS was extracted and characterized using GPC, FTIR and SEM, while its cytotoxicity was tested on RAW 264.7. Sprague Dawley rats were inoculated intranasally with either phosphate-buffered saline (PBS) (Group A), EPS only (Group B), formalin killed whole organism of MhA2 vaccine seed only (Group C) or EPS-MhA2 adjuvanted vaccine (Group D). Serum levels of IgM, IgG, and IgA titers were collected for nine weeks. About 4.8 mg of EPS was obtained in the form of white powder with molecular weight of 2398 Da. The microstructure of EPS was compact and exhibited flakes like structural units and was not toxic to RAW 264.7. EPS-MhA2 group produced significantly higher (p<0.05) IgM, IgG and IgA responses compared to other groups.
