Transcriptional And Functional Regulation Of Eosinophil Development And Recruitment By IL-5Ra And CCR3

In eosinophil-associated allergic diseases, eosinophils are generated and recruited in excess to the site of inflammation. They are activated to release cytotoxic granule proteins that mediate tissue damage and remodeling. For this to occur, two surface receptors, IL-5Rα and CCR3 play important roles in regulating the necessary developmental and functional processes in eosinophils. IL-5Rα is a critical component of the IL-5 signaling pathway responsible for regulating expansion of the eosinophil lineage for development of eosinophilia in allergic diseases. IL-5Rα has two promoters, P1 and P2, both functionally active in eosinophilic cell lines. However, their differential roles and regulation during the development of authentic eosinophil progenitors remain unexplored. By using human umbilical cord blood-derived CD34+ progenitors under IL-5-induced eosinophil differentiation, we elucidated potential non-redundant roles of the two promoters. We found that human IL-5Rα-P1 and -P2 promoters have distinct active windows during eosinophil differentiation, mediated in part through dynamic and combinatorial interactions of stage-specific transcription factors GATA-1, PU.1 and/or the C/EBP family of transcription factors (α, β and ε). The coincidental peak in P2 promoter activity and IL-5Rα soluble isoform mRNA may suggest that this IL-5-binding soluble isoform is induced during eosinophil development to regulate or prevent excessive expansion of the eosinophil lineage in allergic diseases. CCR3 is predominantly expressed by eosinophils, and binding by eotaxins and other chemokines mediates eosinophil tissue recruitment. CCR3 is also expressed by other immune cells comprising the asthma inflammatory infiltrate, and hence represents a valuable therapeutic target. We designed a peptide (R3-2-1) containing a transmembrane domain with extracellular loop portions of CCR3 that self-assembles into uniform nanoparticles. It binds directly to the CCR3 receptor, altering receptor structure and function, inhibiting eosinophil chemotaxis induced by multiple ligands including eotaxin/CCL11 and RANTES/CCL5. R3-2-1 inhibits the MAPK signaling pathway (ERK1/2 phosphorylation) and as a novel biased antagonist, promotes rather than inhibits CCR3 ligand-induced receptor endocytosis. In vivo, R3-2-1 blocks eosinophil recruitment into the esophagus in a mouse model of EoE.