Recombinant Cotton Rat IL-13 Protein

IL‑13 is a 17 kDa immunoregulatory cytokine that plays a key role in the pathogenesis of allergic asthma and atopy. It is secreted by Th1 and Th2 CD4⁺ T cells, NK cells, visceral smooth muscle cells, eosinophils, mast cells, and basophils (1 ‑ 4). IL-13 circulates as a monomer with two internal disulfide bonds that contribute to a bundled four alpha‑helix configuration (5, 6). Mature cotton rat IL‑13 shares 59%, 74%, and 72% amino acid sequence identity with human, mouse, and rat IL‑13, respectively. Despite the low homology, it exhibits cross‑species activity between human, mouse, and rat (7, 8). IL‑13 has diverse activities on numerous cell types (9). On macrophages, IL‑13 suppresses the production of proinflammatory cytokines and other cytotoxic substances. On B cells, IL‑13 induces immunoglobulin class switching to IgE, up‑regulates the expression of MHC class II, CD71, CD72, and CD23, and costimulates proliferation. IL‑13 up‑regulates IL‑6 while down‑regulating IL‑1 and TNF‑ alpha production by fibroblasts and endothelial cells. IL‑13 binds with low affinity to IL‑13 R alpha1, triggering IL‑13 R alpha1 association with IL‑4 R alpha. This high affinity receptor complex also functions as the type 2 IL‑4 receptor complex (10, 11). Additionally, IL‑13 binds with high affinity to IL‑13 R alpha2 which is expressed intracellularly, on the cell surface, and as a soluble molecule (12 ‑ 15). IL‑13 R alpha2 regulates the bioavailability of both IL‑13 and IL‑4 and is overexpressed in glioma and several bronchial pathologies (11, 16, 17). Compared to wild type IL‑13, the atopy‑associated R110Q variant of IL‑13 elicits increased responsiveness from eosinophils that express low levels of IL‑13 R alpha2 (18).