DIFFERENTIAL INHIBITION BY THE PAF RECEPTOR ANTAGONIST, WEB-2170, OF ALLERGIC INFLAMMATION IN SINGLE SENSITIZED AND BOOSTED MICE

Interference of the PAF antagonist, WEB 2170, with the paw edema induced by antigen in boosted or unboosted sensitized mice was investigated. Edema was triggered by the intraplantar injection of ovalbumin to animals actively sensitized 21 days before and that received (boosted), or did not receive (unboosted), a second immunization after 14 days. There was no difference in the intensity of the response to antigen or to PAF (platelet-activating factor) in boosted or in unboosted animals. Intraperitoneal treatment with WEB 2170 1 h before challenge reduced dose dependently the edema in boosted mice but did not modify the reaction in unboosted mice. It is noteworthy that WEB 2170 was more effective against PAF-induced paw edema in unboosted than in boosted mice, the maximum inhibition of 84% being reached at 16 mg/kg. In addition, topical and selective desensitization to PAF inhibited the edema caused by antigen only in boosted animals. Our findings indicate that the booster injection during the immunization process shifts the anaphylactic mouse paw edema from a PAF-independent to a PAF-dependent reaction.