Thymic stromal lymphopoietin stimulates the formation of eosinophil extracellular traps

Abstract

Thymic stromal lymphopoietin (TSLP) that is released by epithelial cells upon certain environmental triggers activates cells of the innate and adaptive immune system resulting in a preferential T helper 2 immune response. By releasing eosinophil extracellular traps (EETs), eosinophils achieve an efficient extracellular bacterial killing. Eosinophil extracellular traps release, however, has been observed in both infectious and noninfectious eosinophilic diseases. Here, we aim to investigate whether eosinophils generate functional EETs as a direct response to TSLP, and further to study the extra- and intracellular mechanisms involved in this process as well as TSLP receptor (TSLPR) expression by eosinophils in vitro and in vivo. Thymic stromal lymphopoietin receptor expression on blood and tissue eosinophils was assessed by immunoblotting, flow cytometry, and immunofluorescence staining. Purified eosinophils were stimulated with recombinant human TSLP. The release of extracellular DNA in association with eosinophilic cationic protein (ECP) was detected by fluorescence staining techniques and confocal microscopy. In addition, cell survival, cell adhesion, production of reactive oxygen species (ROS), and the inhibition of bacterial growth by TSLP-stimulated eosinophils were measured. Thymic stromal lymphopoietin receptor was observed on peripheral blood eosinophils as well as on tissue infiltrating eosinophils in skin diseases. TSLP did not affect eosinophil survival, but induced the formation of EETs consisting of mitochondrial DNA in association with ECP in a concentration- and time-dependent manner. Eosinophil extracellular trap release could be inhibited by blocking either cell adhesion or ROS production. While eosinophils prevented the growth of both Staphylococcus aureus and Staphylococcus epidermidis, the latter were unable to elicit EET formation and eosinophils required additional TSLP stimulation to achieve this antibacterial activity. thymic stromal lymphopoietin directly stimulates eosinophils to produce EETs. Our observations link epithelial TSLP expression triggered by environmental factors with pathogen defense mechanisms involving eosinophils.