Immunostimulatory effects of oriental plum (Prunus salicina Lindl.) Sung-Hyen Lee a,b , Hyun S. Lillehoj a, * , Soo-Muk Cho b , Hye-Kyung Chun b, ** , Hong-Ju Park b , Chai-Il Lim c , Erik P. Lillehoj d a Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705, USA b National Rural Resources Development Institute, National Institute of Agricultural Science and Technology, Rural Development Administration, Suwon 441-853, South Korea c National Horticultural Research Institute, Rural Development Administration, Suwon 441-706, South Korea d Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD 21201, USA Accepted 1 December 2007 Abstract The fruit of the plum tree (Prunus salicina Lindl.) has been used as a traditional medicinal food in humans to enhance immunity against infectious agents and to treat cancers. However, limited information exists on the mechanisms responsible for its immune enhancing properties. In this study, the immunostimulatory effects of a methanol extract of plum fruit following methanol evaporation and dissolving in PBS were assessed by in vitro lymphocyte proliferation, tumor cell cytotoxicity, and nitric oxide (NO) production. The crude methanol extract stimulated spleen lymphocyte proliferation and NO production by cultured macrophages, and inhibited the viability of tumor cells, significantly greater than media controls. Sequential gel filtration chromatographic separation of the extract on Sephadex G-25 and Sephacryl S-200 gel filtration columns resulted in a more purified preparation that retained the ability to induce lymphoproliferation, tumor killing, and NO production. These results suggest that Prunus www.elsevier.com/locate/cimid Available online at www.sciencedirect.com Comparative Immunology, Microbiology and Infectious Diseases 32 (2009) 407–417 * Corresponding author at: Building 1043, BARC-East, Animal Parasitic Diseases Laboratory, Animal and Natural Resources Institute, United States Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705, USA. Tel.: +1 301 504 8771; fax: +1 301 504 5103. ** Corresponding author. E-mail addresses: hlilleho@anri.barc.usda.gov (H.S. Lillehoj), chunhk@rda.go.kr (H.-K. Chun). 0147-9571/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.cimid.2007.12.001