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