SELECTED ARTICLES FROM THE RECENT LITERATURE 2003

12/15/03

Elevated serum tryptase levels predispose to anaphylaxis reactions to insect stings

Summary
The degree of systemic allergic reactions to hymenoptera insect stings varies considerably among venom-allergic individuals. The amount of venom injected by the insect and degree of IgE anti-venom sensitivity in the stung person are thought to determine the severity of such reactions. However, this study by Haeberli et al of Spital Bern Ziegler in Bern, Switzerland suggested that another mechanism may also play a role. They obtained basal serum levels of mast cell-specific enzyme tryptase in a large group of individuals allergic to hymenoptera venom. In 19 of the 259 study subjects, the basal serum tryptase levels were elevated above the normal range. There was skin biopsy evidence suggestive of mastocytosis in 3of such individuals. They found a strong correlation between the serum tryptase level and the reported severity of the previous allergic reaction to the previous sting. In 41 of 161 sting -challenged subjects, an allergic reaction was manifested, The latter was seen disproportionately in those with increased serum tryptase levels in the case of the Vespid-allergic individuals (i.e. - Hornet, wasp) but not in the case of the honeybee venom-allergic patients. The authors suggested that venom immunotherapy has to be carried out cautiously and perhaps for a longer duration in those with increased basal serum tryptase levels because of their increased tendency to manifest anaphylactic reactions.

Reference
Clin Exp Allergy 2003; 33:1216-20

Editor's Comments
The extensive studies by Schwartz's group in Richmond, VA have shown that the total serum tryptase levels (composed of both alpha and beta types of tryptase) generally reflect the "mast cell content" of an individual with serum levels >20 found mainly in those with systemic mastocytosis. Serum levels of the beta-tryptase alone are more reflective of mast cell activation and mediator release seen during systemic allergic reactions such as anaphylaxis. I assume that the assay used in the study described above measured total tryptase reflecting the frequency of mast cells in tissues. It is conceivable
that those with a high frequency of mast cells could manifest a greater total release of mast cell mediators such as histamine with more likelihood of more prominent allergic reactions to a hymenoptera insect sting. However, it is unclear why the bee venom subjects did not fit into that paradigm.
 

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