The antigenicity of an ethylene oxide-treated human serum in humans has been studied. The immune response to the material had many of the characteristics of a delayed cellular skin reaction. Even after repeated immunizations by intradermal skin testing over a period of 1½ years, no detectable antibody could be found in the sera. The antigenicity has been shown to be associated with drastic alteration of the homologous serum proteins as evidenced by (a) the formation of new proteins, and (b) the poor cross-reactions of the modified serum proteins with antisera against normal human serum albumin and normal human gamma globulin.

The delayed hypersensitivity was transferable to normal recipients by either viable or killed leukocytes. The implications of these findings have been discussed with respect to the problem of sterilization of sera, the tuberculin reaction, and autoimmune phenomena.

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