It is now becoming clear that neutrophils and eosinophils are heterogeneous cells with potentially multiple subsets in health and disease. With greater marker coverage by multi-color flow cytometry and single-cell level sequencing of granulocyte populations, novel phenotypes of these cells began to emerge. Intriguingly, many newly described subsets blend distinctions between classical myeloid lineage phenotypes, which are especially true for tissue resident or recruited cells in contexts of inflammation and disease. This includes reports of neutrophils with features of eosinophils, monocytes and dendritic cells, and eosinophil subsets expressing neutrophil markers. Moreover, novel studies show the ability of immature neutrophils to transdifferentiate into mature cells belonging to other myeloid lineages (eosinophils, monocytes/macrophages). In this review, we summarize novel findings in this exciting research frontier and shed light on potential processes driving the plasticity and heterogeneity of granulocyte subsets. Specifically, we discuss the hematopoietic flexibility of granulocyte precursors in bone marrow and the adaptation of myeloid cells to local tissue microenvironments. The understanding of such intermediate and developmental phenotypes is very important, as it can teach us about origins of functionally distinct myeloid cells during inflammation, and explain reasons for successes and failures of biologics targeting terminally differentiated granulocytes.

现在越来越清楚的是，中性粒细胞和嗜酸性粒细胞是异质细胞，在健康和疾病中可能具有多个亚群。随着多色流式细胞术和粒细胞群的单细胞水平测序的更大标记覆盖率，这些细胞的新表型开始出现。有趣的是，许多新描述的亚群融合了经典骨髓谱系表型之间的区别，这对于炎症和疾病背景下的组织驻留或募集细胞尤其如此。这包括具有嗜酸性粒细胞、单核细胞和树突状细胞特征的嗜中性粒细胞以及表达嗜中性粒细胞标志物的嗜酸性粒细胞亚群的报道。此外，新的研究表明未成熟中性粒细胞能够转分化为属于其他骨髓谱系（嗜酸性粒细胞、单核细胞/巨噬细胞）的成熟细胞。在这篇综述中，我们总结了这一激动人心的研究前沿的新发现，并阐明了驱动粒细胞亚群可塑性和异质性的潜在过程。具体来说，我们讨论了骨髓中粒细胞前体的造血灵活性以及骨髓细胞对局部组织微环境的适应。了解这种中间和发育表型非常重要，因为它可以告诉我们炎症期间功能不同的骨髓细胞的起源，并解释靶向终末分化粒细胞的生物制剂成功和失败的原因。我们讨论了骨髓中粒细胞前体的造血灵活性以及骨髓细胞对局部组织微环境的适应。了解这种中间和发育表型非常重要，因为它可以告诉我们炎症期间功能不同的骨髓细胞的起源，并解释靶向终末分化粒细胞的生物制剂成功和失败的原因。我们讨论了骨髓中粒细胞前体的造血灵活性以及骨髓细胞对局部组织微环境的适应。了解这种中间和发育表型非常重要，因为它可以告诉我们炎症期间功能不同的骨髓细胞的起源，并解释靶向终末分化粒细胞的生物制剂成功和失败的原因。