Signal transducer and activator of transcription 3 (STAT3) and Signal transducer and activator of transcription 5A or 5B (STAT5A,STAT5B or STAT5) are phosphorylated after Interleukin 15 (IL15) stimulation of the IL15 receptor complex (Johnston et al. 1995, Lin et al. 1995, Okada et al. 2015, Cooley et al. 2015, Krolopp et al. 2016), which consists of IL15, Interleukin-15 receptor subunit alpha (IL15RA, IL15Rα), Interleukin 2 receptor beta subunit (IL2RB, IL2Rβ), Tyrosine protein kinase JAK1 (JAK1), Cytokine receptor common subunit gamma (IL2RG, IL2Rγ) and Tyrosine protein kinase JAK3 (JAK3).<br>Treatment of human T cells with Interleukin 15 (IL15) and Interleukin 2 (IL2) resulted in the tyrosine phosphorylation of JAK1 and JAK3. Additionally, there was a rapid induction of DNA binding complexes that contained STAT3 and STAT5, both of which were tyrosine phosphorylated (Johnston et al. 1995).This is a black-box event because it is not clear which receptor-associated kinase is responsible for STAT phosphorylation.