Enhancement of resistance to murine osteogenic sarcoma in vivo by an extract of Brucella abortus (Bru-Pel): association with activation of reticuloendothelial system macrophages.

The administration of an aqueous-ether extracted residue of Brucella abortus (Bru-Pel) inhibits development of transplanted osteogenic sarcomas in mice as evidenced by a decrease in mortality. At least one mechanism through which Bru-Pel modulates host resistance is activation of macrophages of the reticuloendothelial system. Peritoneal macrophages harvested from mice receiving Bru-Pel were cytotoxic for osteogenic sarcoma cells in vitro, limited the replication of vaccinia virus in cell cultures, and demonstrated enhanced emittance of chemiluminescence during phagocytosis of zymosan particles of Candida albicans. The concept of reticuloendothelial system activation was further supported by the evidence that administration of Bru-Pel enhanced resistance of mice to challenge with a lethal inoculum of Listeria monocytogenes. These observation support the hypothesis that Bru-Pel shares a number of characteristics with recognized immunomodulating agents and that one mechanism by which it modulates host resistance to tumors, to virus infections, and to challenge with L. monocytogenes is through activation of macrophages.