Complement-Fixation Tests on Rabbits with Brown-Pearce Carcinoma.∗

The recent paper by Cheever1on complement fixing antibodies in rabbits bearing Brown-Pearce tumors, observed by Kidd,2prompts the publication of a similar study carried out in the Spring of 1939 in which similarly positive results were obtained at first, but appeared questionable after the introduction of more rigid controls.The tumor strain was provided by Dr. J. B. Murphy and Mr. Ernest Sturm. Rabbits were inoculated by intratesticular injection. Antigens were prepared and the complement fixation tests carried out as described by Kidd.2aTwenty-five rabbits in all were tested after inoculation with tumor. In the early tests on some 14 rabbits, sera of 3 out of 6 rabbits in which tumors were rapidly developing with many metastases showed definite complement fixation, as compared with 10 negative normal sera used for control. Two other sera were doubtful and one negative. Of 5 animals with small tumors all were negative; and of 3 animals in which tumors indubitably grew and then regressed, all were negative. It may be of interest to note that in 2 of these latter animals kidney metastases appeared to have attained a size of from 3 to 6 mm or larger and subsequently regressed.However, difficulties were encountered in attempts to repeat this experiment. A considerable capacity of some normal sera to fix complement was observed under these conditions, and it was noted that the tumor extracts used as antigen also varied markedly in their complement fixing properties. Prolonged centrifugation, filtration through a Mandler filter, or simply passage of time reduced this tendency to fix complement. Attempts to distinguish more clearly between the sera of the normal and tumor-bearing rabbits by altering the strength of the antigen by dilution were unsuccessful, since a dilution of antigen which eliminated all reactions with normal sera usually also obliterated reactions with the sera of tumor-bearing rabbits.