CCL11/CCR3-dependent eosinophilia alleviates malignant pleural effusions and improves prognosis.

Malignant pleural effusion (MPE) is a common occurrence in advanced cancer and is often linked with a poor prognosis. Eosinophils were reported to involve in the development of MPE. However, the role of eosinophils in MPE remains unclear. To investigate this, we conducted studies using both human samples and mouse models. Increased eosinophil counts were observed in patients with MPE, indicating that the higher the number of eosinophils is, the lower the LENT score is. In our animal models, eosinophils were found to migrate to pleural cavity actively upon exposure to tumor cells. Intriguingly, we discovered that a deficiency in eosinophils exacerbated MPE, possibly due to their anti-tumor effects generated by modifying the microenvironment of MPE. Furthermore, our experiments explored the role of the C-C motif chemokine ligand 11 (CCL11) and its receptor C-C motif chemokine receptor 3 (CCR3) in MPE pathology. As a conclusion, our study underscores the protective potential of eosinophils against the development of MPE, and that an increase in eosinophils through adoptive transfer of eosinophils or increasing their numbers improved MPE.