Signal transducer and activator of transcription 5A/B (STAT5A and/or STAT5B, typically referred to as STAT5) are believed to bind tyrosine-phosphorylated IL7R. Several studies have demonstrated STAT5 phosphorylation following Interleukin‑7 (IL7) ligand‑receptor interaction (Foxwell et al. 1995, van der Plas et al. 1996, Yu et al. 1998, Jufrroy et al. 2010, Landires et al. 2011).
STAT5 is activated in COS7 cells when co‑transfected with JAK3 (Lin et al. 1996), though this does not demonstrate that JAK3 is responsible for STAT5 phosphorylation in vivo (Lin & Leonard, 2000). STAT5 binding is represented here as a black box event as it is inferred to be a prerequisite of IL7-induced STAT5 phosphorylation.