Functional interleukin-33 receptors are expressed in early progenitor stages of allergy-related granulocytes

Abstract

Interleukin-33 (IL-33) induces T helper type 2 (Th2) cytokine production and eosinophilia independently of acquired immunity, leading to innate immunity-mediated allergic inflammation. Allergy-related innate myeloid cells such as eosinophils, basophils and mast cells express the IL-33 receptor (IL-33R), but it is still unknown how IL-33 regulates allergic inflammation involving these cells and their progenitors. Here, we revealed that the functional IL-33R was expressed on eosinophil progenitors (EoPs), basophil progenitors (BaPs) and mast cell progenitors (MCPs). In the presence of IL-33, these progenitors did not expand, but produced a high amount of Th2 and pro-inflammatory cytokines such as IL-9, IL-13, IL-1β and IL-6. The amount of cytokines produced by these progenitors was greater than that by mature cells. In vivo, IL-33 stimulated the expansion of EoPs, but it was dependent upon the elevated serum IL-5 that is presumably derived from type 2 innate lymphoid cells that express functional IL-33R. These data collectively suggest that EoPs, BaPs and MCPs are not only the sources of allergy-related granulocytes, but can also be sources of allergy-related cytokines in IL-33-induced inflammation. Because such progenitors can differentiate into mature granulocytes at the site of inflammation, they are potential therapeutic targets in IL-33-related allergic diseases.

Keywords: basophils; cytokines; eosinophils; haematopoiesis; mast cells.

Figure 1

ST2 is expressed on EoPs, BaPs, MCPs and MEPs in mouse haematopoietic stem/progenitor cells. ST2 expression on mouse haematopoietic stem cells and myeloid lineage cells. Representative data of three independent experiments are shown. HSC, haematopoietic stem cell; MPP, multipotent progenitor; CMP, common myeloid progenitor; GMP, granulocyte/monocyte progenitor; MEP, megakaryocyte/erythrocyte progenitor; EoP, eosinophil progenitor; BaP, basophil progenitor; MCP, mast cell progenitor; PMC, peritoneal mast cell; cDC, conventional dendritic cell.

Figure 2

Interleukin‐33 (IL‐33) induces the expression of genes related to cytokines and chemokines in eosinophil progenitors (EoPs), basophil progenitors (BaPs) and mast cell progenitors (MCPs). A total of 10⁴ cells of EoPs, BaPs or MCPs were cultured in the presence of IL‐3 (1 ng/ml) with or without IL‐33 (50 ng/ml) for 48 hr. The gene expression of (a) cytokines, chemokines and their receptors, (b) adhesion molecules, (c) cell cycle and apoptosis that showed over twofold change are shown. The scale of gene expression signals is shown in the figure.

Figure 3

Eosinophil progenitors (EoPs), basophil progenitors (BaPs) and mast cell progenitors (MCPs) possess a greater potential for cytokine production than mature cells in response to interleukin‐33 (IL‐33). A total of 10⁴ cells of (a) EoPs, (b) BaPs or (c) MCPs were cultured in the presence of IL‐3 (1 ng/ml) with or without IL‐33 (50 ng/ml). The culture supernatants were recovered on day 3 and the cytokine concentrations were determined by multiplex cytokine analysis. Data are shown as mean ± standard deviation of three independent experiments. *P < 0·05.

Figure 4

Interleukin‐33 (IL‐33) does not induce the proliferation of eosinophil progenitors (EoPs), basophil progenitors (BaPs) and mast cell progenitors (MCPs) in vitro. A total of 10⁴ cells of (a) EoPs, (b) BaPs or (c) MCPs were cultured with or without IL‐3 (2 ng/ml) or IL‐5 (2 ng/ml) or IL‐33 (50 ng/ml). The cell numbers were counted on day 2 and day 4 microscopically. Data are shown as the mean ± standard deviation of three independent experiments. *P < 0·05.

Figure 5

Interleukin‐33 (IL‐33) induces the specific expansion of eosinophil progenitors (EoPs) in vivo. IL‐33 (0·5 μg/mouse) was injected into mice on seven consecutive days. Total cell number of each cell population in the (a) spleen, (b) peritoneal cavity and (c) bone marrow was determined. Data are shown as the mean ± standard deviation (n = 3). *P < 0·05.

Figure 6

Interleukin‐33 (IL‐33)‐induced expansion of eosinophil progenitors (EoPs) and eosinophils is dependent on IL‐5. (a) Serum concentration of cytokines in IL‐33‐treated mice. (b) The number of EoPs in the bone marrow or eosinophils in the spleen of IL‐33‐treated mice with or without anti‐IL‐5 antibody injection. (c) IL‐5 expression of IL‐33‐responsive cells in IL‐33‐treated mice. (d) The number of EoPs in peripheral blood. Data are shown as the mean ± standard deviation (n = 3). *P < 0·05.