Prophylactic Effect of Propolis against Tumor Growth in Mice through Stimulation of the Immune System

Propolis (bee glue), a natural product derived from plant resins and collected by honeybees, has numerous biological activities including antibiotic, anti-microbial, antiinflammatory and immunomodulatory properties. The purpose of the present study is to examine the effect of propolis on tumor in mice induced by Ehrlich ascites tumor (EAT) cell line and its possible anti-tumor mechanism of action. Peroral treatment of propolis (0.1, 1 or 10 mg/ 100 g BW) every other day for 4 weeks before the intraperitoneal inoculation of 1x10 EAT cells increased the number of total peritoneal exudate cells (PECs), as well as the absolute number of both macrophages and lymphocytes. The phagocytic function, as determined with carbon clearance assay, was significantly increased. When acquired immune response was evaluated by rosetteforming and plaque-forming assays, a dosedependent increase in both T and B cell activities was observed in propolis-pretreated mice as compared with the tumor-bearing control mice. In vitro studies revealed that propolis with doses (0.01, 0.1 and 1.0 mg/ ml) significantly increased the proliferation of spleen cells in the presence of concanavalin A mitogen. Furthermore, propolis pretreatment effectively decreased the proliferation of EAT cells in the peritoneal fluid, and decreased the viability of EAT cells in vitro. The size of solid Ehrlich tumor was significantly decreased, as measured morphologically and examined histologically. In conclusion, the present findings imply that propolis has a strong inhibitory activity against tumors in mice. The anti-tumor activity of propolis may enhance the host resistance in EAT model through increasing the activities of macrophages, T cells and B cells.