Progressive splenomegaly with increasing extramedullary haematopoiesis in subcutaneous 9L-glioma bearing rats.

We have succeeded in inducing progressive splenomegaly by inoculating 9L-glioma cells into the back subcutaneous regions of Fischer rats. The progressive splenomegaly was histologically characterized by progressively increased extramedullary haematopoiesis. Immunohistochemically Leu 7 positive cells were present in the enlarged spleen, suggesting that the spleen possessed natural killer (NK) cells. However, the splenic NK cell activity obtained in a 4h-51Cr release assay at 5 weeks after inoculation was below 5%, suggesting that the cytotoxic function of the NK cells was depressed. Bone marrow morphologically appeared not to be suppressed. Although the exact cause and mechanism of the progressive splenomegaly with prominent extramedullary haematopoiesis and severe suppression of the splenic NK cell activity remains speculative at present, it could be a unique manifestation of a systemic host-reaction reflected by the 9L-glioma continuously growing in the subcutaneous regions. This experiment could be a useful approach to the study of splenic and other reticuloendothelial roles in host-immunity in the tumour bearing state.