Which of these is false regarding cytokines:
Cytokines mediate their effects by binding to specific high-affinity receptors on their target cells. Specific cytokines mediate specific reactions.

Other important characteristics of cytokines

Cytokines are soluble proteins produced by a wide variety of hematopoietic and non-hematopoietic cells.
They are short acting.

They are required for

Regulation of growth
Activation of the immune system
Mediation of inflammatory response
Mediators of inflammation
Does not mediate specific reactions
Produced by macrophages
Are soluble proteins