Attempts to Abrogate Immunity to the Brown-Pearce Carcinoma*

The cells of the reticuloendothelial system are often regarded as barriers against the development and growth of malignant tumors. Experimental substantiation of this has been obtained by attempts to suppress the functions of these cells by so called blockade methods, and by stimulation of these Cells for the purpose of increasing their functional activity. The former procedure is considered to decrease, and the latter to increase resistance to tumor growth. Blockade of the reticuloendothelial system has been accomplished by the administration of substances that are readily taken up by these cells, such as trypan blue, India ink, etc. Foulds (3) found that the treatment of rabbits with trypan blue before inoculation of the Brown-Pearce carcinoma resulted in a definite increase in the percentage of tumors in the lungs, liver, and spleen. Ludford (6) obtained similar results with a mouse tumor. Stern and Willheim (8) stimulated the reticuloendothelial system in rats by subcutaneous injections of carotin. The treatment was followed by the disappearance of the Flexner-Jobling rat carcinoma and the Jensen rat sarcoma. The following experiment was designed to determine whether or not interference with reticuloendothelial function could break down acquired resistance to tumor growth. For this purpose, animals that had been rendered immune to the Brown-Pearce carcinoma were used. The Brown-Pearce carcinoma is a malignant tumor of the testicle of the rabbit, which, following intratesticular transplantation, grows and metastasizes rapidly and usually kills the animal within 4 to 6 weeks. As has been shown on many occasions (1, 2, 7), intradermal transplantation in the rabbit produces a tumor that increases in size for 3 to 4 weeks, attains its maximum dimensions, and then regresses completely. Following regression of the skin tumor the animals