IL-4 Protein, Rat

Interleukin-4 (IL-4) is a 13–18 kDa, glycosylated, four-α-helix cytokine that was originally described in the rat as “B-cell stimulatory factor-1”. It is synthesized with a 24-aa signal peptide and, once cleaved, the mature rat protein shares ≈41 %, 43 % and 59 % amino-acid identity with bovine, human and mouse IL-4, respectively; cross-species bio-activity is negligible, making rat-specific reagents essential for in-vivo and ex-vivo work. In the rat, IL-4 is produced chiefly by Th2-polarized CD4⁺ T cells, mast cells, basophils and eosinophils, and signals through two receptor heterodimers: the type-I receptor (IL-4Rα + common γ-chain) found on haematopoietic cells, and the type-II receptor (IL-4Rα + IL-13Rα1) expressed on non-haematopoietic cells and shared with IL-13. Engagement of either complex triggers JAK1/3-STAT6 phosphorylation and, secondarily, the IRS-2/PI3K pathway, leading to characteristic Th2 effector functions: IgE and IgG1 class-switching in B cells, alternative (M2) activation of macrophages, mucus production by airway epithelium, and chemotaxis of eosinophils and mast cells. Consequently, IL-4 is the central driver of allergic airway inflammation in rat models of asthma and is routinely used to skew splenocyte cultures toward a Th2 phenotype in vitro.