Activation of human basophils by combined toll‐like receptor‐ and F cε RI ‐triggering can promote T h2 skewing of naive T helper cells

Basophils are mostly known for their involvement in allergic reactions. Recent studies in mice indicate a role for basophils in the induction of adaptive immunity, especially T helper 2 ( T h2) responses. Therefore, it would be highly important to understand how basophils respond to pathogen‐associated molecules, such as ligands for toll‐like receptors ( TLR s), and if the basophils could promote T h2 responses via these stimuli. To this end, the activation of basophils via TLR s in combination with activation via I g E was studied, as well as its effect on T helper cell skewing. Using quantitative PCR , we demonstrated the presence of m RNA for TLR s 1–8 in human basophils. Basophils responded to TLR triggering with differential cytokine production, but not with degranulation. Simultaneous triggering of TLR s and I g E led to synergy in production of IL ‐4, IL ‐8, IL ‐13, and RANTES . Furthermore, the synergistic effects on basophils mediated by I g E and TLR ‐4 triggering allowed robust T h2 skewing upon activation of naïve human CD 4 + T cells. Our data show that human basophils respond to TLR ligands in synergy with I g E ‐mediated activation and that the cytokines produced can promote T h2 differentiation. These results indicate a role for basophils in the regulation of T ‐cell responses in humans.