Figure 1 |. Three modes of cytokine-mediated cell-to-cell communication.

Cells of the immune system communicate through the exchange of secreted cytokines. Depending on the spatial location and identity of the cytokine-consuming cell, such communication can be autocrine (signaling to self), paracrine (signaling to neighboring cells) or endocrine (signaling globally through the circulation). The key parameters that determine the signaling mode are the rate of cytokine production (R_production) and the rate of cytokine consumption (R_consumption). Recent quantitative studies in systems immunology have begun to clarify how cells switch from one mode of signaling to another.