The booster injection of antigen during active sensitization of guinea‐pig modifies the anti‐anaphylactic activity of the PAF antagonist WEB 2086

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Abstract
1 Serum IgG levels of sensitized guinea-pigs bled at various times after the booster injection were evaluated and its capacity to sensitize passively lung strips from normal guinea-pigs assessed. Following the booster injection, both serum IgG and the ability to sensitize passively lung strips increased during the first week and decreased slowly thereafter. 2 The PAF antagonist WEB 2086 (3 mg kg−1, i.v.) blocked the anaphylactic bronchoconstriction induced by intravenous administration of ovalbumin (1 mg kg−1) when guinea-pigs were challenged 2 and 4 days after the booster injection, but became ineffective when tested in guinea-pigs challenged 7, 28 and 56 days after the booster injection. 3 The ability of WEB 2086 to reduce anaphylactic bronchoconstriction of guinea-pigs challenged 2 and 4 days after the booster injection was unrelated to either the selective involvement of one type of immunoglobulin, low IgG titres in sera or a reduced sensitizing capacity. 4 The booster injection, which accounts for the loss of efficacy of WEB 2086 from the fourth day thereafter, probably operates as a PAF-independent inflammatory challenge. 5 The protocol for immunisation and the day of experiment after the booster injection determines the sensitivity of the anaphylactic bronchoconstriction to inhibition by PAF antagonists.

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