Surface membrane changes of T cells induced by syngeneic tumour cells. I. Formation and uptake of complexes of Ig and tumour antigens by T cells.

A large dose of tumour cells (10(7)) from two different tumours produced a significant increase of Ig-bearing spleen cells 6 h after intraperitoneal administration in syngeneic mice, like conventional antigens previously tested. Incubation of normal spleen cells in serum taken 6 h after administration of tumour cells reproduced in vitro the changes observed in the spleen cell population of the serum donors, demonstrating the presence of a cytophilic Ig, which was shown to be taken up by T cells. Serum collected 6 h after tumour cell inoculation contains also a 4S factor which can generate in vitro cytophilic Ig for T cells in the presence of a foreign soluble protein or tumour antigen. Extracts obtained from tumours cells, which were shown to contain tumour antigens, were labelled with 125I and mixed with the 4S factor and normal 7S Ig. Upon fractionation of the mixture, high molecular weight material containing radioactivity and 7S Ig were eluted in the void volume, well ahead of the position of both the tumour cell preparation and the 7S Ig. This material contained Ig cytophilic for splenic T cells and it is likely that it represents cytophilic complexes of Ig and tumour antigens. It is postulated that the cytophilic Ig detected in the serum of animals 6 h after injection of a large number of tumour cells represents cytophilic complexes of Ig and tumour antigens formed through the mediation of a soluble factor.