Trees within the order Fagales possess particularly potent allergens, e.g. the prototypical Bet v1, the major white birch (Betula verrucosa) pollen antigen.

Eventually, after repeated exposures to pollen antigens have stimulated new antibody production, the mast cells burst, releasing various chemicals, including histamine, that are the ultimate cause of allergic symptoms.

Corinti S, De Palma R, Fontana A, Gagliardi C, Pini C, Sallusto F. MHC independent recognition of a distinctive pollen antigen, most likely a carbohydrate, by human CD8+ T cells.