Rat IL‑9 Alexa Fluor™ Plus 647‑conjugated Antibody

Rat interleukin-9 (IL-9; also T-cell growth factor P40 and MEA) is a 20‑30 kDa secreted glycoprotein that belongs to the IL-7/IL-9 family of hematopoietic cytokines. It is best considered an atypical Th2-type cytokine (1‑4). Rat IL-9 was initially isolated from the 4437A rat thymoma cell line (5). The IL-9 precursor is 144 amino acids (aa) in length and contains an 18 aa signal sequence plus a 126 aa mature segment (5). An extended, 219 aa alternate precursor form is reported in GenBank (Accession # XP_001068265). It shows a 113 aa substitution for the first 38 aa of the standard form. Its significance is unknown. Mature rat IL-9 is 75%, 74% and 58% aa identical to cotton rat, mouse and human IL-9, respectively (6‑9). There is variability in cross-species reactivity. Canine and mouse IL-9 are purportedly active on human cells (9‑11), while human IL-9 is inactive on mouse cells (9). Cells reported to express IL-9 include activated CD4+ T cells and eosinophils (12, 13). The receptor for rat IL-9 is composed of the 62 kDa rat IL-9R alpha chain and the 64 kDa rat common cytokine receptor gamma -chain (5, 14, 15). IL-9 is suggested to play a significant, but likely supporting role in allergy and asthma. Its synthesis is induced upon exposure to allergen (10, 13). Following release, it is known to upregulate IgE production by IL‑4‑stimulated B cells (16). It also stimulates mucin secretion and IL-13 production through a direct action on respiratory epithelium (10, 17). In the bone marrow, it promotes eosinophilia, likely through IL-5 induction (18, 19). And once produced, eosinophils are chemoattracted to the bronchi through the IL-9-induced secretion of eotaxin-1 by airway smooth muscle cells (20).