Physiological Level of Eosinophils Is Essential for the Regeneration and Homeostasis of Murine Hematopoietic Stem Cells

Background Eosinophils play a crucial role in host defense and immunity, yet their regulatory functions within the hematopoietic homeostasis remain poorly understood. Our prior investigations revealed that pathologically elevated eosinophil levels in asthma not only disrupt bone marrow hematopoietic stem cell (HSC) quiescence but also establish a self‐reinforcing cycle of eosinophil lineage commitment. Here, we further investigate the critical role of physiologically steady‐state levels of eosinophils in maintaining HSC functions. Methods Using eosinophil lineage‐specific null (Eos‐null) mice, we established models of chemotherapy‐induced HSC regeneration and competitive bone marrow transplantation (cBMT) assay to evaluate the impact of eosinophil depletion on HSC regeneration and function. In vitro colony forming assay assessed HSC reconstitute capability, while bone marrow chimeric mice were established with wild‐type (WT) and eosinophil‐related transgenic mice to further elucidate the role of physiological levels of eosinophils. RNA‐seq and cytokine array analyses were utilized to investigate the potential protective mechanisms of eosinophils. Results Compared to WT controls, Eos‐null mice exhibited significantly impaired HSC regeneration, characterized by a diminished response to 5‐fluorouracil (5‐FU) and carboplatin treatment. Both long‐term HSCs (LT‐HSCs) and lineage − Sca‐1 + c‐Kit + (LSK) demonstrated compromised reconstitution capacity in vivo and in vitro. HSCs from Eos‐null mice demonstrated elevated apoptosis under 5‐FU treatment, potentially due to the absence of eosinophil‐derived protective factors. Conversely, both chimeric mice and eosinophil incorporation within bone marrow transplantation systems significantly disrupted HSC homeostasis and function. Conclusion Physiological eosinophil level is essential for maintaining HSC regeneration, reconstitution capacity, and homeostasis.