Page 223 - Veterinary Immunology, 10th Edition

VetBooks.ir Cytokine Structure

Cytokines are very diverse proteins. They can be classified based on
their structures or on their functions (Table 8.1). Structurally, many

fall into four major groups. The group I cytokines (or
hematopoietins), consist of four α helices bundled together. This
group can be subdivided into three families: the interferon family,
the IL-2 family, and the IL-10 family. All facilitate communication
between lymphocytes and epithelial cells. Group II cytokines

consist of long-chain β-sheet structures. They include the TNF
family and the IL-1 family. The IL-1 family includes seven agonist
cytokines, three receptor antagonists, and one antiinflammatory

cytokine. IL-1 family members require proteolytic processing by
enzymes such as caspases to achieve full biological activity. Group
III cytokines include the chemokines and related molecules, small
proteins with both α helices and β sheets. Group IV cytokines are
heterodimers that use mixtures of domains and structural motifs

and include the IL-12 family and the IL-17 family. Many cytokines,
such as IL-14, IL-16, and IL-32, are structurally unique and do not
belong to any of these major families.

TABLE 8.1

Molecular Classification of Selected Cytokines

Structural Structure Examples
Families
Group 1 Four α helix IL-2, -3, -4, -5, -6, -7, -9, -11, -13, -15, -21; GM-CSF, erythropoietin, G-CSF, prolactin,
bundle leptin, TSLP.
IFN subfamily IFN-α/β, IFN-γ,IFN−λ
IL-10 subfamily IL-10, -19, -20, -22, -24, -26, -28, -29
Group 2 β Sheets TGF-β
IL-1 family IL-1α, -1β, -18, -33, -36, -37, -38,
TNF family TNFs, BAFF
Group 3 α Helices and β Chemokines
sheets
Group 4 Mixed motifs
IL-12 family IL-12, -23, -27, -30, -35, -39
IL-17 family IL-17A-F. IL-17F is also called IL-25
Ungrouped Unique structures IL-14, -16, -32
Patterns may also be seen in their biological activities. Thus
group I cytokines tend to be involved in immune regulation or stem
cell regulation. Group II cytokines are mainly involved in the

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