Signal transducer and activator of transcription 3 (STAT3) is believed to bind the Interleukin-19 (IL19) /Interleukin-19 receptor complex. IL19 stimulates transient STAT3 phosphorylation and translocation from the cytoplasm to the nucleus (Dumoutier et al. 2001, Tian et al. 2008, Jain et al.2011). STAT3 binding is inferred to be a prerequisite for its phosphorylation from the signaling mechanism of the related interleukin-10 receptor, which is able to bind and phosphorylate STAT3 (Riley et al. 1999). The IL19 receptor complex consists of Interleukin-20 Receptor A (IL20RA) associated with Tyrosine-protein kinase JAK1 (JAK1) and Interleukin-20 receptor B (IL20RB). This is a black box event because binding of STAT3 after IL19 stimulus has not been demonstrated.