Rosenberg, Helene F.

Abstract Eosinophil effector functions have been hypothesized to be mediated in part by the release of proteins stored in the secondary granules of mature cells of this leukocyte lineage. Major basic protein-1 (MBP-1) and eosinophil peroxidase (EPO) comprise the majority of protein in these granules. No role has been speculated for these proteins in eosinophilopoiesis and/or the accumulation of mature cells in circulation. Methods: Eosinophilopoiesis and eosinophil accumulation in the periphery were assessed in single and double knockout (MBP-1-/- and/or EPO-/-) mice. Bone marrow and peripheral blood leukocytes were assessed by IHC, FACS and in vitro cell culture assays. Mice were subjected to an acute OVA protocol assessing induced pulmonary pathologies in each of the strains of granule protein knockout mice. Results: We demonstrate that, unlike the single deficiency of MBP-1 or EPO, the absence of both granule proteins resulted in the loss of peripheral blood eosinophils. IHC assessments of bone marrow and spleen demonstrate that eosinophil lineage commitment occurs in these mice. However, these assessments and FACS studies demonstrated a blockade in the maturation of eosinophil-lineage committed cells. This blockade is not rescued by ex vivo culture or by bone marrow engraftment into wild type recipient mice. Similar to other eosinophil-less mouse models, MBP-1-/-/EPO-/- mice also fail to develop pulmonary inflammation in an OVA protocol.

Abstract Although eosinophils as a group are readily identified by their unique morphology and staining properties, flow cytometry provides an important means for identification of subgroups based on differential expression of distinct surface Ags. Here, we characterize an eosinophil subpopulation defined by high levels of expression of the neutrophil Ag Gr1 (CD45+CD11c−SiglecF+Gr1hi). SiglecF+Gr1hi eosinophils, distinct from the canonical SiglecF+Gr1− eosinophil population, were detected in allergen-challenged wild-type and granule protein-deficient (EPX−/− and MBP-1−/−) mice, but not in the eosinophil-deficient ΔdblGATA strain. In contrast to Gr1+ neutrophils, which express both cross-reacting Ags Ly6C and Ly6G, SiglecF+Gr1hi eosinophils from allergen-challenged lung tissue are uniquely Ly6G+. Although indistinguishable from the more-numerous SiglecF+Gr1− eosinophils under light microscopy, FACS-isolated populations revealed prominent differences in cytokine contents. The lymphocyte-targeting cytokines CXCL13 and IL-27 were identified only in the SiglecF+Gr1hi eosinophil population (at 3.9 and 4.8 pg/106 cells, respectively), as was the prominent proinflammatory mediator IL-13 (72 pg/106 cells). Interestingly, bone marrow-derived (SiglecF+), cultured eosinophils include a more substantial Gr1+ subpopulation (∼50%); Gr1+ bmEos includes primarily a single Ly6C+ and a smaller, double-positive (Ly6C+Ly6G+) population. Taken together, our findings characterize a distinct SiglecF+Gr1hi eosinophil subset in lungs of allergen-challenged, wild-type and granule protein-deficient mice. SiglecF+Gr1hi eosinophils from wild-type mice maintain a distinct subset of cytokines, including those active on B and T lymphocytes. These cytokines may facilitate eosinophil-mediated immunomodulatory responses in the allergen-challenged lung as well as in other distinct microenvironments.

Key Points Eosinophils recruited to the airways in response to A fumigatus sensitization and challenge degranulate in response to virus infection. Activated eosinophils are antiviral and promote survival from an otherwise lethal respiratory virus infection.

Key PointsThe loss of the two most abundant eosinophil granule proteins disrupts the production of blood eosinophils from marrow progenitors. Knockout animals deficient for both MBP-1 and EPX represent a novel strain of mice with a specific and congenital loss of eosinophils.

AbstractWe explore the controversial issue of the role of eosinophils in host defense against helminthic parasites using the established Schistosoma mansoni infection model in 2 novel mouse models of eosinophil lineage ablation (ΔdblGATA and TgPHIL). No eosinophils were detected in bone marrow of infected ΔdblGATA or TgPHIL mice, despite the fact that serum IL-5 levels in these infected mice exceeded those in infected wild type by approximately 4-fold. Liver granulomata from infected ΔdblGATA and TgPHIL mice were likewise depleted of eosinophils compared with those from their respective wild types. No eosinophil-dependent differences in granuloma number, size, or fibrosis were detected at weeks 8 or 12 of infection, and differential accumulation of mast cells was observed among the ΔdblGATA mice only at week 12. Likewise, serum levels of liver transaminases, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) increased in all mice in response to S mansoni infection, with no eosinophil-dependent differences in hepatocellular damage observed. Finally, eosinophil ablation had no effect on worm burden or on egg deposition. Overall, our data indicate that eosinophil ablation has no impact on traditional measures of disease in the S mansoni infection model in mice. However, eosinophils may have unexplored immunomodulatory contributions to this disease process.