Dendritic cells (DCs) sample the airway lumen by forming dendritic extensions between epithelial cells. Enzymatically active allergens, like house dust mite can stimulate airway epithelial cells, via TLR(toll-like receptor)4 followed by NF-κB (nuclear factor-κB) activation, to produce chemokines and cytokines that attract and activate DCs. Certain cytokines, like IL(interleukin)-25 and IL-33 will lead to the upregulation of OX40L, CD40 and ST2, which will lead to polarization of CD4+ T cells towards a Th2 phenotype. Other cytokines like IL-1α and β activate DCs, but also have a positive autocrine feedback on epithelial cells and further stimulate the production of TSLP and GM-CSF. Abbreviations: DC, dendritic cell; EC, epithelial cell; GM-CSF, granulocyte-macrophage colony stimulating factor; HDM, house dust mite; IL, interleukin; NF-κB, nuclear factor-κB; TLR, toll-like receptor; TSLP, thymic stromal lymphopoietin.