Table 1.

List of AT-derived adipokines and their biologic functions

Adipokine	Immunobiologic function in AT	Ref
Leptin	Activates CD4 T cells and induce their production of TNF-α, IL-6, and IL-12 Activates MCs and induces the release of cysLTs Hypothalamic modulator of food intake, the regulator of energy expenditure Upregulates monocyte activation markers including CD11b, CD11c, MHC class II, CD25, CD38, and CD69 Promotes neutrophil chemoattraction and the production of ROS Leptin deficiency-induced obesity correlates with increased MCs in abdominal lymph nodes	[29] [30] [30] [29] [29] [31]
Adiponectin	The most abundant peptide secreted by adipocytes Acts as a regulator of thermogenesis Antagonizes TNF-α expression in adipocytes and macrophages Acts through AdipoR1 (mainly expressed in skeletal muscle) and AdipoR2 (predominantly expressed in the liver) Promote M2 macrophage polarization and improves insulin sensitivity	[23] [32] [29] [23] [33]
Lipocalin-2 (LCN2)	Also known as neutrophil gelatinase-associated lipocalin (NGAL) Upregulated in the presence of IFN-γ and TNF-α in obese individuals	[25] [29]
Retinol-binding protein 4 (RBP4)	Promotes IR and increases the T2D risk Majority of circulating RBP4 is found in complex with retinol RBP is a cardiometabolic marker in chronic pathologic conditions including MetS Activates APCs	[34] [35] [36] [36]
Fibroblast growth factor 21 (FGF21)	Regulates glucose and fat metabolism under fasting condition It is inactivated by fibroblast activation protein alpha (FAP-α) Engages its receptor FGFR1 and co-receptor β-Klotho Involved in fatty acid oxidation and lipid metabolism improves glucose tolerance	[37] [37] [38] [29]
Resistin	Produced mainly by macrophages and acts as an inflammatory molecule Secreted mainly by AT in rodents and macrophages in humans Regulates the production of TNFα and IL-6 in macrophages via activation of NF-κB signaling Binds to TLR4	[29] [39] [39] [39]
Visfatin	Also known as a pre-B cell colony-enhancing factor (PBEF), involved in chemoattraction of neutrophils Induces the production of cytokines in monocytes Acts through insulin receptor-1 and possesses hypoglycemic effect Activates monocytes, promotes the secretion of IL-1β, TNF-α, and IL-6	[28] [28] [27] [29]
Monocyte chemotactic protein-1 (MCP1)	Mediated the infiltration of monocyte and macrophage to the site of inflammation Its expression correlates with body BMI and adiposity	[40]
Fetuin-A	Promotes IR by inhibition of insulin receptor’s tyrosine kinase activity Mainly secreted by the liver and taken up by AT AT secreted fetuin-A increases in metabolic syndrome	[34] [41] [42]