Epicutaneously applied Der p 2 induces a strong T(H)2-biased antibody response in C57BL/6 mice, independent of functional TLR4

BACKGROUND: The major house dust mite allergen Der p 2 is a structural and functional homologue of MD-2 within the TLR4–CD14–MD-2 complex. An asthma mouse model in TLR4-deficient mice recently suggested that the allergic immune response against Der p 2 is solely dependent on TLR4 signaling. We investigated whether similar mechanisms are important for Der p 2 sensitization via the skin. METHODS: In an epicutaneous sensitization model, the response to recombinant Der p 2 in combination with or without lipopolysaccharide (LPS) was compared between C57BL/6 WT and TLR4-deficient mice. We further analyzed possible adjuvant function of exogenous cysteine proteases. RESULTS: Sensitization with rDer p 2 induced similar levels of allergen-specific IgG1 and IgE antibodies in both mouse strains. LPS increased the systemic (antibody levels, cytokine release by restimulated splenocytes) and local (infiltration of immune cells into the skin) Th2 immune responses, which against our expectations were stronger in the absence of functional TLR4 expression. Barrier disruption by papain, a protease with structural homology to Der p 1, did not enhance the sensitization capacity of rDer p 2. However, the presence of LPS increased the stability of rDer p 2 against the protease. CONCLUSION: Our data suggest that rDer p 2 alone can cause a strong T(H)2-biased response via the skin being enhanced in the presence of LPS. This response is not reliant on functional TLR4, but vice versa TLR4 expression rather protects against epicutaneous sensitization to house dust mite allergen Der p 2.