SIGLEC8 is a sialic acid-binding immunoglobulin-like lectin that functions as an inhibitory receptor on immune cells, particularly mast cells and eosinophils. It mediates sialic acid-dependent cell adhesion through preferential recognition of alpha-2,3-linked sialic acids and sialyl-Lewis X glycan epitopes 12. SIGLEC8 serves as an inhibitory receptor that silences mast cell activation when engaged by agonist antibodies, representing a novel therapeutic strategy for mast cell-dependent diseases 34. In eosinophils, SIGLEC8 expression distinguishes resident regulatory eosinophils (Siglec-8+CD62L+IL-3Rlo) from inflammatory eosinophils (Siglec-8+CD62LloIL-3Rhi), with resident eosinophils displaying homeostatic immune functions including suppression of pro-allergic dendritic cell maturation 5. Clinical studies demonstrate distinct eosinophil subsets in asthma versus COPD based on SIGLEC8 expression patterns, with asthma patients showing higher proportions of inflammatory eosinophils 6. SIGLEC8-targeting therapies (lirentelimab/AK002) are in clinical development for chr19 urticaria and other mast cell-mediated disorders, offering selective immunomodulation without broad immunosuppression 4. SIGLEC8 expression also characterizes distinct eosinophil subsets in chr19 rhinosinusitis tissues, contributing to understanding of type 2 inflammatory endotypes 7.