Spatial distribution of alpha-gal in Ixodes ricinus – A histological study

Alpha-gal syndrome is a complex allergic disease in humans that is caused by specific IgE (sIgE) against the carbohydrate galactose-α-1,3-galactose (alpha-gal). Tick saliva contains alpha-gal, and tick bites are considered a major cause of the induction of alpha-gal-sIgE. The origin of alpha-gal in tick saliva remains unclarified. The presence of alpha-gal in tick tissue was visualized in this study to provide an overview of the spatial distribution of alpha-gal and to further elucidate the origin of alpha-gal in tick saliva. Fed and unfed Ixodes ricinus females were examined by histology, immunohistochemistry, immunofluorescence, transmission electron microscopy and immunoelectron microscopy using the alpha-gal-specific monoclonal antibody M86 and Marasmius oreades agglutinin (MOA) lectin. Alpha-gal epitopes were detected in the midgut, hemolymph and salivary glands, and the immunofluorescence analysis revealed signs of the endocytosis of alpha-gal-containing constituents during the process of hematophagy. Alpha-gal epitopes in endosomes of the digestive gut cells of the ticks were observed via immunoelectron microscopy. Alpha-gal epitopes were detected in dried droplets of hemolymph from unfed ticks. Intense staining of alpha-gal epitopes was found in type II granular acini of the salivary glands of fed and unfed ticks. Our data suggest that alpha-gal is not ubiquitously expressed in tick tissue but is present in both fed and unfed ticks. The findings also indicate that both the metabolic incorporation of constituents from a mammalian blood meal and endogenous production contribute to the presence of alpha-gal epitopes in ticks.