Recombinant Rat IL-9R Protein

The IL-9 receptor alpha protein is a member of the type I cytokine receptor family. It is a 62 kDa IL-9 receptor subunit (previously Gfi-2, designated CD129) that binds IL-9 and pairs with the 64 kDa cytokine receptor common gamma-chain to allow cell signaling (1 - 3). The 467 amino acid (aa) rat IL-9 R alpha precursor is predicted to contain a 37 aa signal sequence, a 232 aa extracellular domain (ECD) with four conserved cysteine residues in its N-terminal region, a fibronectin type III domain and a WSXWS motif, a 21 aa transmembrane (TM) domain, and a 177 aa cytoplasmic domain with a Box 1 JAK-binding motif (1, 2, 4). A potential isoform contains a 36 aa sequence that is substituted for the TM and cytoplasmic domains (5). The ECD of rat IL-9 R alpha shares 86%, 63%, 66%, 63% and 59% aa identity with the ECD of mouse, human, equine, canine and bovine IL-9 R alpha, respectively. Mast cells, germinal center and B-1b B cells, T cell blasts, and myeloid progenitors express IL-9 R (1, 6 - 8). The primary functions of IL-9 have been difficult to determine due to the cross-functionality and cross-induction of cytokines. IL-9 production by regulatory T cells (T-regs), however, is crucial for mast cell recruitment and differentiation, which in turn is crucial for tolerance of allografts (7). Genetic deletion and transgenic expression of IL-9 and other cytokines has also demonstrated the role of IL-9 in mastocytosis, eosinophilia and B cell infiltration of the lung in a mouse asthma-like model, while IL-9 induction of IL-13 is responsible for eosinophil recruitment and mucous upregulation (8 - 10).