HAMP and nutritional disorder: Interestingly, IL-6 induces hepcidin, which negatively affects erythropoiesis by inducing iron deficiency (Nemeth et al., 2004), whereas cytokines such as IL-18 and IL-23 (which are produced by monocytes and/or macrophages in addition to other cells) increase IFN-γ production (Nakamura et al., 1989).