Serum factor levels during the growth of rat hepatoma nodules in the lungs

The levels of tumour-specific antigen, antibody and specific immune complexes in the sera of rats bearing lung nodules of a chemically induced rat hepatoma, produced by intravenous inoculation of viable tumour cells, have been examined and compared with the levels of serum factors in animals actively immunized by intravenous inoculation of mixed tumour cells and BCG. Animals inoculated with cells alone developed multiple lung nodules which slowly grew, until on day 24 the remaining animals had to be killed due to respiratory distress. In contrast, the animals receiving a mixed inoculum of BCG and tumour cells developed no visible lung nodules and were capable of rejecting a further challenge of tumour cells. Tumour-specific antigen could be detected in the sera of both groups of rats at different times. In actively immunized animals free antigen could be detected from day 3 to day 10 after inoculation of cells BCG whereas in animals receiving cells alone, free antigen could not be detected until day 14 and persisted until the termination of the experiment. Free tumour-specific antibody, however, was found in the sera of rats actively immunized with tumour cells and BCG from day 10 onwards, although in the other group of animals it could not be detected. Conversely, immune complexes of tumour-specific antigen and antibody could be detected from day 10 in rats receiving cells alone and only at day 10 in actively immunized rats. The relevance of these findings in relation to what is known about serum factor levels during tumour growth and regression is discussed.