GPR43 in eosinophils prevents the emergence of pathogenic Siglec-Fhi neutrophils in allergic airway inflammation

Eosinophils are major effector cells in type 2 immune responses, contributing to host defense and allergic diseases. They also play critical roles in maintaining tissue homeostasis by regulating various immune cell types. However, evidence of the crosstalk between eosinophils and neutrophils is limited. Here, we show that eosinophils directly associate with neutrophils in the lungs of asthma-induced mice. Eosinophil-specific deficiency of the short-chain fatty acid receptor GPR43 results in hyperactivation of eosinophils and increases the expression of neutrophil chemoattractants and PECAM-1, thus enhancing the interaction between eosinophils and neutrophils. This binding event exposes the neutrophils to eosinophil-derived IL-4 and GM-CSF, which induces the conversion of conventional neutrophils into more pathogenic Siglec-Fhi neutrophils that strongly enhance Th17 cell differentiation and aggravate asthma symptoms. These results reveal GPR43 as a critical regulator of eosinophils and highlight that eosinophils have a hitherto little-known ability to directly modulate neutrophil differentiation and function. One Sentence Summary Eosinophils directly recruit neutrophils and induce their differentiation into a pathogenic Siglec-Fhi subset in allergic airway inflammation.