Evidence that the elevated levels of proteinase activity in the plasma of melanoma-bearing mice may be of host origin

C57B1/6 mice bearing the B16-F1 melanoma, an invasive variant (BL6) or a highly 'metastatic' variant (B16-F10) were found to develop elevated levels (200-300% of control) of neutral proteinase activity in their plasma during the progression of the disease. The magnitude of the level of proteinase activity detected was not dependent on tumor burden. Similar elevations in activity were detected with all 3 variants when they were transplanted either subcutaneously or intraperitoneally. However, transplantation of the B16-F10 line to the anterior chamber of the eye did not induce elevated plasma proteinase activity. Animals bearing intraocular tumors developed splenomegaly and lived the same length of time as animals bearing intraperitoneal or subcutaneous tumors. The development of increased levels of activity appeared to occur equally in male and female mice and was not dependent on the presence of a spleen, which undergoes enlargement during the disease process. These various lines of evidence support the hypothesis that the elevated level of plasma proteinase activity observed in melanoma-bearing mice is regulated by the host.