Molecular mimicry as the key to the dominance of the house dust mite allergen Der p 2

The majority of complex sources of allergen contain a small number of dominant allergens that bind at least half of the IgE antibodies of allergic subjects. For the house dust mite Dermatophagoides pteronyssinus, these allergens are Der p 1 and Der p 2. There is evidence that the cysteine-protease activity of Der p 1 imparts adjuvant activity to the allergen. It has now been shown that Der p 2 mimics the activity of its fellow ML-domain protein, MD-2, by presenting lipopolysaccharide to Toll-like receptor-4 for the activation of inflammatory genes. In accord with this, Der p 2 presented with lipopolysaccharide also induced enhanced type 1 allergic sensitization of mice, even when they were deficient in MD-2. The mimicry of MD-2 can thus also self adjuvant Der p 2 to enhance it allergenicity. This not only describes an intriguing mechanism for enhancing allergenicity but also, since both of the dominant mite allergens have intrinsic adjuvant activity, exemplifies an important principle for driving allergic sensitization.