Isolation of soluble immunosuppressive substance(s) from Ehrlich ascites tumor cell nuclei

A potent immunosuppressive principle was isolated in a soluble form from the nuclei of Ehrlich ascites tumor cells. DNA-free preparation, obtained from the purified nuclei by homogenizing in 2M NaCl-5M urea solution and removing the dissociated DNA with LaCl3-precipitation, revealed strong activity to suppress the development of helper thymus-derived lymphocyte activity in mice. Moreover, almost all of the immunosuppressive activity originally found in the nuclear residue fraction after extraction with sodium citrate solution was recovered in 0.25 N HCl extract which mainly contains proteins. The nuclear components of tumor cells were also detected in the body fluid of tumor-bearing animals, as examined by the reactivity with a rabbit antiserum specific for some nuclear component of Ehrlich tumor cells. These results suggest that the immunosuppressive principle in the nuclei of Ehrlich tumor cells is a histone-like substance, and liberated into the body fluid from tumor cell nuclei in the tumor-bearing state.