Background: Immunoglobulin (Ig) E–mediated reactions to honeybee venom can cause severe anaphylaxis, sometimes with fatal consequences. Detailed knowledge of the allergic potential of all venom components is necessary to ensure proper diagnosis and treatment of allergy and to gain a better understanding of the allergological mechanisms of insect venoms.

Objective: Our objective was to undertake an immunochemical and structural evaluation of the putative low-molecular-weight serine protease inhibitor Api m 6, a component of honeybee venom.

Methods: We recombinantly produced Api m 6 as a soluble protein in Escherichia coli and in Spodoptera frugiperda (Sf9) insect cells. We also assessed specific IgE reactivity of venom-sensitized patients with 2 prokaryotically produced Api m 6 variants using enzyme-linked immunosorbent assay. Moreover, we built a structural model of Api m 6 and compared it with other protease inhibitor structures to gain insights into the function of Api m 6.

Results: In a population of 31 honeybee venom–allergic patients, 26% showed specific IgE reactivity with prokaryotically produced Api m 6, showing it to be a minor but relevant allergen. Molecular modeling of Api m 6 revealed a typical fold of canonical protease inhibitors, supporting the putative function of this venom allergen. Although Api m 6 has a highly variant surface charge, its epitope distribution appears to be similar to that of related proteins.

Conclusion: Api m 6 is a honeybee venom component with IgE-sensitizing potential in a fraction of venom-allergic patients. Recombinant Api m 6 can help elucidate individual component-resolved reactivity profiles and increase our understanding of immune responses to low-molecular-weight allergens.

Key words: Api m 6. Apis mellifera. Honeybee venom. Hymenoptera venom. Insect venom allergy. Protease inhibitor. Recombinant allergen. sIgE.