Description
Rat interleukin-9 (IL-9; also T-cell growth factor P40 and MEA) is a 20-30 kD 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 kD rat IL-9Ra chain and the 64 kD rat common cytokine receptor g-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 IL9-induced secretion of eotaxin-1 by airway smooth muscle cells