IL13 and primary cutaneous T-cell non-Hodgkin lymphoma: The malignant T cells have also been shown to produce IL-31, which together with IL-4, IL-5 and IL-13, is believed to stimulate the sensation of pruritus in CTCL patients (Ohmatsu et al., 2012; Singer et al., 2013; Cedeno-Laurent et al., 2015; Nattkemper et al., 2016; Lewis et al., 2018).