The activities of cytokines are pleiotropic and interdependent

Many cytokines with multiple effects on the growth and functions of a wide variety of target cells have been discovered. Consequently, cytokines may exhibit considerable overlap in their biological effects on lymphoid, myeloid and connective tissue target cells. Even biologically distinct cytokines may have similar effects by initiating the production of a cascade of identical cytokines or of one another. The benefits of this apparent redundancy and interdependence of these activities remain to be established. Our information concerning cytokines is still far from complete, as illustrated by the recent characterization of a novel chemotactic cytokine and identification of a family of related mediators.