Tyrosine-protein kinase JAK1 (JAK1) is believed to be phosphorylated after Interleukin-19 (IL19)/IL19 receptor interaction. The IL19 receptor complex is identical to one of the two Interleukin-24 (IL24) receptors ((Dumoutier et al. 2001, Wang et al. 2002). IL24 can stimulate JAK1 phosphorylation in human colonic subepithelial myofibroblasts, where the components of both forms of the IL24 receptor are expresed (Andoh et al. 2009). Although it was not established that both forms of the IL24 receptor were involved in JAK1 phosphorylation, it has been demonstrated that the IL19 receptor when stimulated with IL19 and both forms of the IL24 receptor when stimulated with IL24 can activate STAT3 (Dumoutier et al. 2001, Wang et al. 2002). Based on the consensus understanding of JAK/STAT signaling, STAT3 activation is very likely to be preceded by JAK1 phosphorylation and it is therefore likely that both forms of the IL24 receptor, including the form that is also a receptor for IL19, lead to JAK1 phosphorylation. This reaction is a black box event because there is no experimental data confirming JAK1 phosphorylation in response to IL19.