Demonstration of accelerated and increased migration inhibition factor release in vivo in a PPD retest reaction.

Sites at which positive skin-test reactions have been elicited exhibit an accelerated (so-called 'retest') reaction upon local reinjection of the antigen used for primary skin testing. When using a peritoneal cavity inflammation model in guinea pigs, local migration inhibition factor (MIF) release in vivo was studied in both primary and retest reactions to purified protein derivative. Increased retest reactivity could be demonstrated to coincide with an instantaneous and intense local MIF release. Estimation of both the absolute number of the antigen specificity of lymphocytes present in the peritoneal cavity at the time of retesting (170 h after primary testing) showed that the early burst of MIF release is primarily due to nonspecific local retention of increased numbers of lymphocytes.