What are the properties of cytokines?

The majority of cytokines are small helical-bundle proteins, ranging from 150-200 amino acids in length and molecular weights from 6-70 kDa. There are 2 classes of cytokines based on motifs located in their receptors (Class I and II cytokines). Class I cytokines are composed of 4 alpha helices in an up-up-down-down configuration. Class II cytokines have an additional alpha-helix (5-6 helices in total), organized in an antiparallel configuration. Cytokines regulate cellular activity through the processes of pleiotropy, synergy, antagonism, and redundancy. Pleiotropism refers to a cytokine's ability to affect multiple cell types. This process is possible because fewer cytokines exhibit an endocrine effect, permitting them to have various effects on different cells. Redundancy is the process of having various cytokines with the same effects in the body. During the process of redundancy, it is difficult to attribute a specific activity to a single cytokine since various cytokines can induce similar responses. Synergy refers to the process when the combined effect of two cytokines in their activity is more than the sum of their individual effects. Antagonism occurs when the effects of one cytokine inhibits or reduces the effects of another cytokine. This process is the opposite of synergy.