Immunodepression, ascites tumour and lactate dehydrogenase virus.

The delayed hypersensitivity (DH) response to picryl chloride was studied in Ehrlich ascites tumour-bearing and normal control mice. A significant depression of the DH response was found in the tumour-bearing mice, which was associated with a marked elevation of serum lactate dehydrogenase (LDH). Depression of DH was also observed in mice receiving cell-free ascitic fluid. These mice also showed an elevated serum LDH which is assumed to be associated with the lactate dehydrogenase virus. A method for assaying DH in vivo is described.