Interleukin-5 (IL-5) is a secreted glycoprotein that belongs to the alpha -helical group of cytokines [1 - 3]. Unlike other family members, it is present as a covalently linked antiparallel dimer [4, 5]. The cDNA for mouse IL-5 encodes a signal peptide and a 113 amino acid (aa) mature protein. Mature mouse IL-5 shares 70%, 94%, 58%, 66%, 59% and 63%, aa sequence identity with human, rat, canine, equine, feline and porcine IL-5, respectively, and shows cross-reactivity with human IL-5 receptor. IL-5 is primarily produced by CD4+ Th2 cells, but also by activated eosinophils, mast cells, EBV-transformed B cells, Reed-Sternberg cells in Hodgkin's disease, and IL-2-stimulated invariant natural killer T cells (iNKT) [1 - 3, 6 - 8]. IL-5 increases production and mobilization of eosinophils and CD34+ progenitors from the bone marrow and causes maturation of eosinophil precursors outside the bone marrow [1, 6, 9, 10]. The receptor for human IL-5, mainly expressed by eosinophils, but also found on basophils and mast cells, consists of a unique ligand-binding subunit (IL-5 R alpha ) and a shared signal-transducing subunit, beta c [3, 6, 11]. IL-5 R alpha first binds IL-5 at low affinity, then associates with preformed beta c dimers, forming a high-affinity receptor [12].
Reference
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