Antitumor activity of cell walls from Brucella abortus

The ip inoculation of inactivated Brucella abortus, strain B19 R, protected mice against a subsequent graft of an ascites lymphoma. The bacterial components responsible for this effect were investigated. Centrifugation supernatants of sonicated bacteria supposed to contain mainly cytoplasmic products did not offer protection against the lymphoma. Cell walls (CW's) prepared by enzyme digestion of pellets of lysed bacteria and checked for purity by electron microscopy prolonged survival of mice and induced cytotoxic macrophages in their peritoneal cavities. CW peptidoglycan (PG) did not seem to play an important part in this effect. Enzyme digestion of CW, in particular by lysozyme, was found to reduce a PG characteristic component (diaminopimelic acid) without altering CW antitumor activity. Conversely, a purified PG preparation did not influence tumor growth. Extraction of CW by an ether:water mixture did not alter its antitumor activity, while incubation in NaOH abolished its activity almost completely. All CW preparations were found to elicit hypersensitivity reactions in Brucella-infected animals.