A thymic stromal lymphopoietin-responsive dendritic cell subset mediates allergic responses in the upper airway mucosa

Background: Thymic stromal lymphopoietin (TSLP) controls allergic T(H)2 inflammatory responses through induction of distinct activation programs in dendritic cells (DCs). However, knowledge about TSLP receptor expression and functional consequences of receptor activation by DCs residing in the human respiratory tract is limited. Objective: We wanted to identify TSLP-responding DC populations in the human upper airway mucosa and assess the TSLP-mediated effects on such DCs in allergic airway responses. Results: We found that the TSLP receptor was constitutively and preferentially expressed by myeloid CD1c(+) DCs in the human airway mucosa and that the density of this DC subset in nasal mucosa increased significantly after in vivo allergen challenge of patients with allergic rhinitis. In vitro, TSLP strongly enhanced the capacity of CD1c(+) DCs to activate allergen-specific memory CD4(+) T cells. Moreover, TSLP rapidly induced CCR7 expression on CD1c(+) DCs. However, T(H)2 cytokines attenuated TSLP-mediated CCR7 induction, thus inhibiting the TSLP-induced DC migration potential to the draining lymph nodes. Conclusion: Our results suggest that TSLP-mediated activation of human nasal mucosal CD1c(+) DCs triggers CCR7-dependent migration to the draining lymph nodes and enhances their capacity to initiate T(H)2 responses. However, the observation that T(H)2 cytokines abrogate the induction of CCR7 implies that during a T(H)2-mediated inflammatory reaction, TLSP-activated CD1c(+) DCs are retained in the inflamed tissue to further exacerbate local inflammation by activating local antigen-specific memory T(H)2 cells.