title: Antitumor activity with nontoxic doses of protein A.
abstract: This report confirms our previous observation that IV inoculation of purified protein A causes regression of rat mammary adenocarcinomas. In treated tumors, we have obtained histological evidence of changes indicating tumor cell destruction. Protein A treatment does not cause reduction in the body weight or organ weights of rats; nor does it cause any decrease in activity of the enzymes of the microsomal mixed function oxidase system in the liver. Protein A stimulates peripheral white cell counts in normal rats, but not in tumor-bearing rats. We found that protein A infusion reduced (P less than 0.0005) the level of circulating plasma immune complex concentration. A homing study with 125I-labeled protein A indicated that liver, spleen, and kidney tissues are the major sites of protein A accumulation. Therefore, protein A seemed to exert its antitumor effects without causing any generalized toxicity to the system. It is postulated that the action of protein A may be related to its ability to cause a drastic reduction in circulating plasma immune complex concentration, thus potentiating the immune reactivity of the host observed earlier.
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology / Q000628:therapy*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D005260:Female; D007167:Immunotherapy; D008325:Mammary Neoplasms, Experimental / Q000473:pathology / Q000628:therapy*; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D013205:Staphylococcal Protein A / Q000627:therapeutic use*
chemical_list: D013205:Staphylococcal Protein A