Specific depression of delayed hypersensitivity to purified proteins, with relation to production of circulating antibody

In guinea pigs sensitized in the footpads with a purified protein, such as hen egg albumin or diphtheria toxoid, in incomplete Freund's adjuvant, delayed hypersensitivity precedes the appearance of circulating antibody. This expression of delayed hypersensitivity by skin-test declines sharply the day before circulating antibody is detected. Adoptive transfer of spleen and peritoneal exudate cells from guinea pigs showing this decline suppresses the expression of delayed hypersensitivity in already sensitized recipients. This suppression of delayed hypersensitivity is immunologically specific. The intensity of this suppression does not correlate directly with the dose of sensitizing antigen, nor does it depend directly on the amount of circulating antibody.