Tumor-specific changes in mouse serum during Ehrlich carcinoma growth

Using the method of flow cytofluorometry we found that proteinase activity eliminating antigenic determinants from the surface of tumor cells disappeared from the serum of mice with Ehrlich carcinoma. This activity towards Ehrlich carcinoma cells is present in the sera of mice without tumors and in mice with other transplanted tumors. The serum from mice of one strain with Ehrlich carcinoma showed no protease activity against Ehrlich carcinoma cells in mice of other strain. Hence, Ehrlich carcinoma growth is associated with tumor-specific changes in the serum resulting in disappearance of specific protease activity of the serum against tumor cells.