Diagram of Simple Diffusion-Consumption Kinetics. Cytokines are secreted by a producing cell and freely diffuse between cells. Upon binding to a receptor, the cytokine is endocytosed, or consumed. This creates a gradient of localized cytokine niche with a typical length scale of μniche. Increasing consumers will lead to a decrease in the μniche and vice versa. When μniche is small relative to the total organ size, increases in cell-to-cell variability are likely. (Reprinted from Immunity, Vol 46, Oyler-Yaniv A et al, A Tunable Diffusion-Consumption Mechanism of Cytokine Propagation Enables Plasticity in Cell-to-Cell Communication in the Immune System, pp 609-620, Copyright 2017, with permission from Elsevier).