Translational research presented at EAACI 2026 upends conventional understanding of allergic contact dermatitis (ACD). The study indicates B cells, long considered scarce and irrelevant in type IV hypersensitivity, play a key role in shaping skin inflammation and tolerance to contact allergens.
Investigators analyzed circulating B cells from healthy controls, patients allergic to the hair dye allergen p-phenylenediamine (PPD), and PPD-tolerant individuals. Single-cell RNA sequencing revealed distinct transcriptional signatures between allergic and tolerant groups. In vitro studies showed differential B-cell proliferation and cytokine responses based on clinical phenotype.
A parallel murine model offered mechanistic clarity. Mice in a PPD-induced ACD model underwent tolerance induction using the vitamin D analogue MC903. Tolerance correlated with regulatory-like B-cell states, while allergies showed inflammatory B-cell profiles. Crucially, B-cell depletion led to exaggerated and prolonged skin inflammation. MC903-driven tolerance promoted dermal infiltration of regulatory B cells.
The findings establish B cells as active contributors to the balance between inflammation and tolerance in ACD. The data suggest combining allergen exposure with immunomodulatory signals could reprogram B cells toward regulatory phenotypes, dampening skin inflammation. This challenges the view of skin as B-cell independent and opens avenues for B-cell-targeted therapies in chronic inflammatory skin diseases.