Atopic dermatitis (AD) is one of the most common inflammatory skin diseases worldwide and Staphylococcus aureus colonization and secondary infections occur in the majority of AD patients. Allergic sensitizations against microbial antigens have been discussed as possible trigger factors of AD. Recently, we reported IgE sensitization against fibronectin‐binding protein 1 (FBP1), an essential virulence component in S. aureus, in a subgroup of patients suffering from AD. To expand these findings by investigating delayed‐type immune reactions, the objective of this study was to detect and phenotypically characterize FBP1‐specific T cells as possible trigger factors in AD.

Immunodominant T‐cell epitopes were mapped by proliferation testing of patient‐derived FBP1‐specific T‐cell lines after stimulation with single 15mer peptides, which were derived from different functional domains of the FBP1 sequence. Major histocompatibility complex class II tetramers carrying immunodominant epitopes successfully stained T helper cells in 8 out of 8 HLA‐matched, IgE‐sensitized AD patients.

Cytokine profiling of multimer‐sorted cells revealed that predominantly the type 2 cytokines IL‐13 and IL‐4 were secreted by these cells. In contrast, IL‐17, the marker cytokine for response to extracellular pathogens, was scarcely detectable.

We demonstrate that FBP1 contains immunodominant peptides that induce a specific pro‐inflammatory T helper cell response with increased Th2 levels that can drive an allergic inflammation in sensitized AD patients.