Effect of frequency of plasma adsorption over protein A-containing Staphylococcus aureus on regression of rat mammary adenocarcinomas: modification of antitumor immune response and tumor histopathology.

Adsorption of the plasma of Sprague-Dawley rats having 7, 12-dimethylbenzanthracene (DMBA)-induced primary mammary adenocarcinomas with protein A-containing Staphylococcus aureus Cowan I (SAC) and reinfusion of the adsorbed plasma caused significant (p less than 0.05) regression of mammary adenocarcinomas. Adsorption of plasma was done at different intervals--weekly, biweekly, and on alternate days. Of these protocols, alternate-day adsorptions induced very fast (within a week) tumor regression (p less than 0.001). Other protocols also produced tumor regression; however, the effect was delayed. In long-term studies, the responding animals showed fewer tumor nodules than did the untreated controls. The plasma of the treated animals showed (a) a reduction in blocking activity, (b) an increase in antibody- and complement-mediated cytotoxicity, and (c) potentiation of the cytotoxic activity of peripheral blood mononuclear cells (PBMCs). Histopathological analyses of biopsied sections of tumors from treated animals showed (a) disruption of tumor cell architecture, (b) loss of glandular structure, (c) shrinkage of epithelial cells, and (d) moderate mononuclear cell infiltration. Thus, adsorption of the plasma of DMBA tumor-bearing rats with SAC allows an indigenous immune mechanism to function against autochthonous tumors to control their growth and cause regression.