Ambrosia artemisiifolia allergen 9 (Amb a 9)

Amb a 9 is a low-molecular-weight (approximately 9 kDa) calcium-binding protein identified in the pollen of short ragweed (Ambrosia artemisiifolia). It belongs to the polcalcin family and contains two EF-hand motifs that facilitate calcium ion binding, a function critical for pollen germination and tube growth. In humans, Amb a 9 acts as an aeroallergen that induces Type I hypersensitivity reactions, contributing to seasonal allergic rhinitis, conjunctivitis, and asthma. It is characterized as a "pan-allergen" due to its high structural homology and IgE cross-reactivity with polcalcins from other taxonomically unrelated plants, such as mugwort and various grasses. Clinically, Amb a 9 is a target for component-resolved allergy diagnostics and allergen-specific immunotherapy (AIT), which aim to induce immune tolerance. Therapeutic strategies involve the use of ragweed pollen extracts to modulate the immune system toward a regulatory T cell response and the production of protective IgG4 antibodies.

Other names

PolcalcinCalcium-binding proteinrAmb a 9Short ragweed calcium-binding protein

Allergen-specific immunotherapy (AIT) utilizes the molecule to induce immunological tolerance by shifting the immune response from Th2-driven inflammation to a Th1/Treg profile and promoting the production of allergen-specific IgG4 antibodies that block IgE-mediated activation.