Published Online: March 15, 2013
Several studies have found high baseline serum tryptase levels to be predictive of a higher risk for an anaphylactic response following a Hymenoptera (insects including bees, wasps, and ants) sting. Baseline serum tryptase levels are a parameter of mast cell load, a high baseline serum level may indicate the presence of mastocytosis. Mastocytosis is a rare disorder characterized by a high mast cell load and frequent anaphylactic reactions to Hymenoptera stings, with sometimes lethal consequences. Given these relations, it is tempting to speculate that the high mast cell load is at least partially responsible for the high prevalence of anaphylactic reactions to Hymenoptera venom in mastocytosis.
In a recent issue of The Journal of Allergy and Clinical Immunology, van Anrooij et al. examined the relationship between mast cell load and anaphylactic reactions to Hymenoptera venom in 329 mastocytosis patients, revealing a surprising dichotomous relationship. Mast cell load was assessed using the mast cell load parameters baseline serum tryptase, in addition to the less well known histamine metabolites urinary methylimidazole acetic acid and urinary methylhistamine. Seventy-five of the patients had developed an anaphylactic reaction following a Hymenoptera sting, and the data from these patients revealed a surprising association with mast cell load. Initially, the risk of anaphylaxis increased with mast cell load, as demonstrated in other studies. However, after reaching a plateau the risk declined with further rising of the mast cell load. Because nearly all of the patients with a positive history for an anaphylactic reaction to Hymenoptera venom suffered from the indolent systemic form of mastocytosis, these patients were further investigated. In this group, nearly half of the patients with adult exposure to Hymenoptera venom developed an anaphylactic reaction. Multivariate logistic regression revealed that mast cell load (both tryptase as well as urinary histamine metabolites) turned out to be an independent predictor associated with a lower risk for an anaphylactic reaction to Hymenoptera venom.
The authors’ findings demonstrate a hitherto unknown protective association between mast cell load and the risk for an anaphylactic reaction to Hymenoptera venom. The mechanisms governing this association require further research, but the authors speculate on multiple pathways through which high mast cell load could modulate immunity. The authors suggest that the manner in which mast cell load parameters (such as the often used baseline serum tryptase), should be interpreted as risk factors for an anaphylactic response depend on the presence of an underlying mast cell disorder such as mastocytosis. This study demonstrates that the idea that the higher the tryptase the higher the risk of anaphylaxis is too simple. If an underlying mast cell disorder is present a high tryptase is associated with a lower risk.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.