Frontline Science: Cytokine-Mediated Developmental Phenotype Of Mouse Eosinophils: Il-5-Associated Expression Of The Ly6g/Gr1 Surface Ag

Eosinophils have broad and extensive immunomodulatory capacity; recent studies have focused on the roles of distinct eosinophil subsets in specific tissue microenvironments. Ly6G is a GPI-linked leukocyte surface Ag understood primarily as a marker of mouse neutrophils, although its full function is not known. Here, we show that Ly6G/Gr1, detected by mAbs 1A8 (anti-Ly6G) and RB6-8C5 (anti-Gr1), is detected prominently on a significant fraction of eosinophils from mouse bone marrow and bone marrow-derived culture, with fractions expressing this Ag increasing in IL-5-enriched microenvironments. Among our findings, we identified SiglecF(+)Gr1(+) eosinophils in bone marrow from naive, allergen-challenged and IL-5 transgenic mice; SiglecF(+)Gr1(+) eosinophils were also prominent ex vivo in bone marrow-derived eosinophils (bmEos) in IL-5-enriched culture. Reducing the IL-5 concentration 20-fold had no impact on the rate of generation of SiglecF(+) bmEos but did result in a marked increase in the Gr1(-) fraction (from 17.4 +/- 2% to 30 +/- 2.3%, ***P < 0.005). Reducing the IL-5 concentration also enhanced chemotaxis; SiglecF(+)Gr1(-) bmEos were considerably more responsive to eotaxin-1 than were their SiglecF(+)Gr1(+) counterparts. These results suggest that (i) IL-5 regulates the expression of Ly6G/Gr1, either directly or indirectly, in cells of the eosinophil lineage, (ii) eosinophils generated in response to high concentrations of IL-5 can be distinguished from those generated under homeostatic conditions by expression of the Ly6G/Gr1 cell surface Ag, and (iii) expression of Ly6G/Gr1 may have an impact on function, directly or indirectly, including the potential to undergo chemotaxis in response to eotaxin-1.