In situ imaging of honeybee (Apis mellifera) venom components from aqueous and aluminium hydroxide adsorbed venom immunotherapy preparations

Background: Treatment with aqueous and aluminium hydroxide (Al(OH)3)-adsorbed purified honeybee (Apis mellifera) venom (HBV) preparations can reduce incidence of side effects associated to venom immunotherapy (VIT). Objective: The aim of the present study was to assess these purified HBV immunotherapy preparations in situ. Methods: Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) was used to visualize the distribution of HBV components. The preparations were administered on the back leg of naïve Wistar rats. The rats were sacrificed and cryosectioned tissue sections were subjected to hematoxilyn & eosin (H&E) staining and MALDI MSI analyses. Results: Low density maps of tissue distribution of HBV peptides such as secapin, mast cell degranulating peptide (MCD) and mellitin (Api m 4) were detected in the tissue after administration of HBV immunotherapy preparations. In addition, release of biogenic amines, cytokines and leukotrienes was observed and distribution of HBV allergens such as Api m 1 and Api m 2 was shown. At the 24 hour time point the major HBV allergen, Api m 1 was still detected at site of Al(OH)3 –adsorbed HVB injection whereas in the case of aqueous HBV preparation all the allergens as well as most of the biogenic amines were cleared at 24 hr time point.