Immunocytochemical localization of allergenic proteins in Parietaria judaica L (Urticaceae) pollen grains

Inhalation of pollen grains and fungal spores leads to allergenic rhinitis and type I asthma mediated by IgE. The etiology of these conditions is due to the presence of substances that can induce anaphylactic processes in susceptible subjects. A combination of transmission electron microscopy with immunocytochemical methods was used to localize allergenic proteins in Parietaria judaica L. (Urticaceae) pollen grains. Germination of pollen grains was induced in vitro for 10 and 30 min to activate proteins in the intine and in material exuded from the pollen grains that are related to pollen-stigma recognition; these activated proteins would be the ones that react with the antibodies. The activation time, labeling intensity and specificity of the antigens depended on whether IgG (rabbit) or IgE (allergenic patient) was used. Abundant, non-specific labeling was observed with rabbit IgG. The labeling observed with human IgE was located more specifically in the intine (oncus) at random points near the apertures. The immunolocalization of allergenic proteins in the intine indicates the presence of proteins related to activation of the pollen grains. This fact confirms the function attributed to the intine in the processes of pollen tube formation and fertilization, and also the possible mechanism that is activated in the pollen grains when these reach the mucosa of sensitive subjects. In the case of P. judaica, the existence of a thickening of the intine below the apertures (oncus) and the release of its contents in an explosive fashion seem to be the main causes of their strong allergenic activity.