Inhibitory effect of honeybee-collected pollen on mast cell degranulation in vivo and in vitro

Bee-collected pollen (bee pollen [BP]) has been used as a folk medicine for centuries against various diseases, including allergy. There is no study elucidating how BP exerts such an anti-allergic effect. Since mast cells play a central role in the pathogenesis of various allergic diseases, we investigated the effect of BP on mast cell activation elicited by the Fc immunoglobulin E (IgE) receptor (Fc epsilon RI)-mediated pathways. The in vivo effect of orally administered BP on cutaneous mast cell activation was examined by passive cutaneous anaphylaxis reaction. In vitro mast cell degranulation and IgE binding to mast cells and the status of protein tyrosine phosphorylation were examined using bone marrow-derived mast cells. Daily oral administration of BP to mice significantly reduced the cutaneous mast cell activation elicited by IgE and specific antigens. BP also reduced in vitro mast cell degranulation and tumor necrosis factor-alpha production by inhibiting IgE binding to Fc epsilon RI on mast cells. The inhibitory effect of BP on mast cell degranulation by preventing IgE binding was confirmed by the reduced levels of protein tyrosine phosphorylation, which occurred as downstream events in activated mast cells via Fc epsilon RI. These results first revealed that the anti-allergic action of BP was exerted by inhibiting the Fc epsilon RI-mediated activation of mast cells, which plays important roles, not only in the early phase, but also in the late phase of allergic reactions.