Epicutaneously applied <scp>D</scp>er p 2 induces a strong <scp>T_H</scp>2‐biased antibody response in <scp>C</scp>57<scp>BL</scp>/6 mice, independent of functional <scp>TLR</scp>4

Background The major house dust mite allergen D er p 2 is a structural and functional homologue of MD ‐2 within the TLR 4– CD 14– MD‐ 2 complex. An asthma mouse model in TLR 4‐deficient mice recently suggested that the allergic immune response against D er p 2 is solely dependent on TLR 4 signaling. We investigated whether similar mechanisms are important for D er p 2 sensitization via the skin. Methods In an epicutaneous sensitization model, the response to recombinant D er p 2 in combination with or without lipopolysaccharide ( LPS ) was compared between C 57 BL /6 WT and TLR 4‐deficient mice. We further analyzed possible adjuvant function of exogenous cysteine proteases. Results Sensitization with r D er p 2 induced similar levels of allergen‐specific I g G 1 and I g E 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 TLR 4 expression. Barrier disruption by papain, a protease with structural homology to D er p 1, did not enhance the sensitization capacity of rD er p 2. However, the presence of LPS increased the stability of r D er p 2 against the protease. Conclusion Our data suggest that r D er 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 TLR 4, but vice versa TLR 4 expression rather protects against epicutaneous sensitization to house dust mite allergen D er p 2.