Characterization of the T‐cell response to Dau c 1, the Bet v 1‐homolog in carrot

Background In contrast to other Bet v 1‐related food allergens, the major carrot allergen, Dau c 1, has been suggested to induce food allergy independently from Bet v 1. As T cells are crucial in the sensitization process, we sought to characterize the T‐cell response to Dau c 1 and its cross‐reactivity with Bet v 1. Methods Dau c 1‐specific T‐cell lines ( TCL ) and clones ( TCC ) established from PBMC of birch pollen‐allergic patients with carrot allergy were analyzed for reactivity to Bet v 1, epitope specificity, allergen‐induced cytokine secretion, and expression of integrins α4β7 and α4β1, critical for gut and lung homing, respectively. mRNA expression of GATA 3 and Tbet was analyzed in sorted CD 3 + CD 4 + CFSE low cells proliferating upon stimulation of PBMC with Dau c 1 or Bet v 1. Dau c 1 was incubated with endolysosomal proteases, and the resulting fragments were identified by mass spectrometry. Results Among 14 distinct T‐cell‐activating regions, Dau c 1 139–153 was recognized by 55% of the patients. Only 6 of 15 (40%) Dau c 1‐specific TCL and 9 of 21 (43%) TCC reacted with Bet v 1. Bet v 1‐nonreactive TCC were mainly Th1‐like and showed a higher expression of the integrin β7 and a significantly lower expression of the integrin β1 than Bet v 1‐positive TCC . A Th1‐like response was also detected in Dau c 1‐reactive CD 3 + CD 4 + CFSE low cells. Full‐length Dau c 1 was still detectable after 48 h of endolysosomal degradation. Proteolytic fragments of Dau c 1 matched its T‐cell‐activating regions. Conclusion Dau c 1 displays several characteristics of sensitizing allergens, namely a major T‐cell‐activating region, low susceptibility to endolysosomal degradation, and induction of a Bet v 1‐independent T‐cell response. These cellular insights confirm that the major carrot allergen has a special status among Bet v 1‐related food allergens.