Activation profile of THP-1 derived dendritic cells stimulated by allergen Mal f 1 beyond its IgE-binding ability

Mal f 1, the first allergen cloned from Malassezia furfur, has positive IgE reactivity in sera from atopic dermatitis (AD) patients. The mechanism by which Mal f 1 induces the maturation of human dendritic cells (DCs) and maintains the symptoms of AD is not well understood.

The present study aims to explore the activation profile of THP-1 derived dendritic cells (TDDCs) stimulated by recombinant Mal f 1, as well as to explore the IgE-binding ability of rMal f 1 and its correlation with IgE-binding activity of complete allergens of M. furfur.

rMal f 1 was produced by expression in E. coli and purification with affinity chromatography. The ability of rMal f 1 and ImmunoCAP complete allergens of M. furfur to bind to serum specific IgE was assayed in parallel by ELISA and immunoblotting. Immature TDDCs were stimulated with rMal f 1 or an enzyme-digested product of rMal f 1. The expression levels of markers, CD83, CD80, CD86, and HLA-DR, were investigated by flow cytometry. The levels of interleukin (IL)-6, IL-10, IL-12p70 and tumor necrosis factor (TNF)-α in culture supernatants were determined by ELISA.

Eighteen patient sera were identified that reacted positively to the complete allergens of M. furfur as determined by ImmunoCAP and also showed positive responses to rMal f 1. Five patient sera were identified that had no reaction to ImmunoCAP complete allergens of M. furfur and also exhibited negative response to rMal f 1. All sera, except for one, had no reaction to the unrelated allergen Bet v 1. rMal f 1 upregulated the maturation surface marker CD83 on TDDCs. In addition, rMal f 1 also induced high levels of CD80 and CD86. Increased expression of HLA-DR, a first signal for T cell activation, was observed. Secretion of IL-6, TNF-α and IL-10 by TDDCs increased significantly (P < 0.0001 for IL-6, P < 0.01 for TNF-α and P < 0.05 for IL-10) after stimulation by rMal f 1, while the IL-12p70 level was unaltered.

We have shown that rMal f 1 has ideal IgE binding ability and good correlation with binding activity to M. furfur. Moreover, we have revealed a hitherto unknown DC activation profile after rMal f 1 stimulation whereby TNF-α, IL-6, and IL-10 were significantly increased and IL-12 was unaltered, suggesting that rMal f 1 can predispose a DC bias toward the T_H22/T_H17 pathway beyond the routine IgE-dependent T_H2 pathway, thus providing intriguing clues for clinical treatment involving both pathways.