Loss of NF-κB-inducing kinase (NIK) affects eosinophilopoiesis in a murine model of Hypereosinophilic syndrome

Nuclear factor-kappa B (NF-κB)-inducing kinase (NIK), an upstream regulator of the noncanonical NF-κB signaling pathway, is implicated in the development of Hypereosinophilic syndrome (HES) in mice. HES in human patients is defined by 1.5 × 109 cells/L circulating in the blood with end-organ infiltration and resultant tissue damage. In mice lacking the NIK gene (Map3k14), the mechanisms underlying eosinophilopoiesis have not been fully elucidated, although previous studies have demonstrated a connection between Th2 helper T cells and HES in Nik-/- mice. We hypothesize that NIK also influences the development and education of eosinophils in the hematopoietic tissues independent of T-cell involvement. We developed an in vitro bone marrow microenvironment, and utilized MTT and BrdU assays coupled with cytology, flow cytometry, BCL-XL ELISA, and an inflammation antibody array to show that Nik-/- eosinophils demonstrate altered metabolism, survival, and maturation when compared to wild-type eosinophils in response to an altered microenvironment and cytokine milieu. Furthermore, the Nik-/- in vitro bone marrow microenvironment contains lower levels of free tumor necrosis factor receptor 1 (TNFR1) and more consistent surface-bound TNFR1 when compared to wild-type counterparts. Additionally, we explored the heterogeneity of granulocyte differentiation in the Nik-/- model. Here, we demonstrate that in vivo, Nik-/- mice contain significantly higher counts of both mature and immature eosinophils, and a population of eosinophils expressing neutrophil marker Ly6G, which may represent a unique population subset of eosinophils. Overall, these data indicate that NIK influences eosinophil maturation, differentiation, and responsiveness to the surrounding microenvironment.