Change in the role of the spleen from protective to harmful following tumor progression in AKR lymphoma.

Tumor progression has been reported to be often accompanied by a loss of sensitivity to various elements of the immune system. In the present study, three variants of malignancy of AKR lymphoma were compared as to the host reaction they elicit. Splenectomy caused an acceleration of growth of the low-metastasizing tumor, slightly inhibited the growth of the tumor of intermediate malignancy and significantly inhibited the development of the high-metastasizing lymphoma. These results suggest that splenic elements exert an inhibitory effect on the low-metastasizing tumor and a growth-stimulatory effect on the more malignant ones. While decreased sensitivity to various host defense mechanisms following tumor progression has been amply documented, the present study shows a more severe phenomenon: increased malignancy can be accompanied by a deviation of the host immune reaction from tumor growth inhibition to growth stimulation.