Delayed Hypersensitivity and the Anamnestic Response

Delayed hypersensitivity developed in the absence of detectable antibody in guinea pigs injected in the footpads with either 0.1 Lf diphtheria toxoid or 0.5 μg egg albumin in physiologic saline. A secondary injection of specific antigen into animals with delayed hypersensitivity but no circulating antibody produced an anamnestic response. The anamnestic response, as determined by the length of the induction period, was at its peak about the time delayed hypersensitivity was at a maximum. Injection of only 0.0001 Lf induced slight, questionable delayed hypersensitivity, and a slight anamnestic response after a secondary injection of toxoid. Total body irradiation with 200 r 18 hr before either primary or secondary sensitization did not inhibit the anamnestic response.