Tube leukocyte adherence inhibition assay for the detection of anti-tumour immunity. II. Monocyte reacts with tumour antigen via cytophilic anti-tumour antibody.

The peripheral blood monocyte is the reactive cell in the tube LAI assay. The monocyte loses its properties of adherence to glass upon exposure to specific antigen. Two different experiments to determine if lymphocytes, when they reacted with tumour, released mediators that were responsible for inhibiting monocyte glass adherence, gave negative results. The mechanism wherby the specific tumour antigen appeared to be recognized was the binding of cytophilic IgG antitumour antibody to receptors on the cell surface of the monocyte. The results of the experiments indicate that normal peripheral blood monocytes could be made specifically reactive ("armed") to the tumour extract by incubating normal peripheral blood leukocytes with serum from a reactive cancer patient. IgG isolated from "arming" sera was shown to have the capacity to sensitize normal leukocytes. Patients with breast cancer or malignant melanoma with limited tumour burdens had free cytophilic anti-tumour antibody in their serum, whereas the serum of patients with large tumour burdens (metastatic cancer), whose leukocytes did not react in the tube LAI assay, did not "arm".