Scientific Study

Background: The underlying mechanisms of an immediate food-induced allergic reaction involve mast-cell degranulation and recruitment of other effector cells, such as lymphocytes, eosinophils, and basophils. How the interaction of various mediators and cells results in anaphylaxis is not fully understood. Objective: To evaluate changes in platelet-activating factor (PAF), platelet-activating factor acetylhydrolase (PAF-AH), tryptase, eosinophils, basophils, and eosinophil cationic protein (ECP) in cashew nut-induced anaphylaxis. Methods: Open cashew nut challenges were performed on 106 children (aged 1-16 years), sensitized to cashew nut, with earlier allergic reaction to cashew nut or no known exposure. PAF, PAF-AH, tryptase, ECP, eosinophils, and basophils were measured at four timepoints. Results: 34/72 (47%) positive challenges were defined as anaphylactic. Eosinophil count decreased progressively during an anaphylactic reaction at all four timepoints (P< .005*) compared to baseline. Although significant PAF elevation was observed 1 hour from moderate-to-severe reaction (P= .039*), PAF seemed to peak especially in anaphylaxis but did not achieve statistical significance. PAF peak ratio (peak PAF/baseline PAF) was significantly greater in anaphylactic reactions compared to the no-anaphylaxis group (P= .008*). Maximal percentage change in eosinophils revealed negative correlation to severity score and PAF peak ratio (Spearman's rho -0.424 and -0.516, respectively). Basophils decreased significantly in moderate-to-severe reactions and in anaphylaxis (P< .05*) compared to baseline. Delta-tryptase (peak tryptase minus baseline) did not differ significantly between anaphylaxis and the no-anaphylaxis subgroups (P= .05). Conclusion: PAF is a specific anaphylaxis biomarker. Marked decline of eosinophils during anaphylaxis may be related to robust secretion of PAF reflecting migration of eosinophils to target tissues. https://doi.org/10.1016/j.anai.2023.04.014