Signal transducer and activator of transcription 5A or 5B (STAT5A and/or STAT5B, typically referred to as STAT5) are phosphorylated after 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 phosphorylates STAT5 proteins in response to IL7 in vivo (Lin & Leonard, 2000). STAT5 phosphorylation is represented here as a black box event because it is not clear which JAK kinase phosphorylates STAT5 in vivo.