Macrophages and lymphoid tissues in mice with concomitant tumour immunity.

The growth in mice of subcutaneous isografts of any of 5 methylcholanthrene-induced fibrosarcomas was associated with macrophage stimulation, reflected in an increased incidence of DNA-synthesizing cells among marcophages in the uninjected peritoneal cavity. This occurred at some stage with 4 tumours that induced concomitant immunity and one that did not. Some degree of splenomegaly also occurred with all 5 tumours. The spleens of all the tumour-bearing mice showed histological evidence of increased haemopoietic activity. Histological changes in the lymphoid elements of the spleen were very different with different tumours, ranging from lymphoid stimulation to lymphoid atrophy. The lymph nodes draining the sites of primary isografts which induced concomitant immunity showed signs of stimulation in the paracortical areas, followed by plasmacytopoiesis in the medullary areas. Stimulation of the paracortical areas was not detected in the nodes draining sites of injection of a tumour not inducing concomitant immunity. Nodes draining the sites of challenge isografts in mice exhibiting concomitant immunity showed plasmacytopiesis.