Thymic stromal lymphopoietin stimulates the formation of eosinophil extracellular traps

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Identification of a novel mutation in the coding region of the grey-lethal geneOSTM1in human malignant infantile osteopetrosis

Autosomal recessive malignant infantile osteopetrosis (ARO) is characterized by severe osteosclerosis, pathologic fractures, hepatosplenomegaly, and pancytopenia. The pathophysiological basis is inadequate bone resorption due to osteoclast dysfunction. In the majority of cases, mutations in either of two human genes cause this fatal disorder: TCIRG1, encoding a subunit of the osteoclast H(+)-ATPase, and the voltage-gated chloride channel gene CLCN7. We excluded both genes in a small inbred family with malignant infantile osteopetrosis and undertook linkage analysis of several candidate loci that are involved in murine osteopetrosis. A region spanning more than 20 cM between the markers D6S1717 and D6S1608 on chromosome 6q21 was found to be homozygous in the affected child. This locus is syntenic to the genomic region harboring the gene for the osteopetrotic mutant mouse grey-lethal (gl). Recently, mutations in a novel gene of unknown function were described in the grey-lethal mouse and in one human patient. Mutation screening of the grey-lethal gene (OSTM1), revealed a homozygous 2-bp deletion in exon 2 (c.415_416delAG) in the affected child. No mutations could be found in six independent ARO patients who had tested negative for mutations in TCIRG1 and CLCN7. In summary, we describe the identification of a novel mutation in the coding sequence of the human grey-lethal gene, which is the second OSTM1 mutation found in human ARO, confirming the involvement of this gene in the pathogenesis of this severe bone disease.