ABSTRACT
Th e major functions of interleukins (IL) are to regulate via cell-cell signaling the responses of an organism to an immune challenge. Whereas the major site of production and secretion of interleukins as well as their major targets are leukocytes, some interleukins are also produced and secreted by adipocytes, defi ning them as another class of adipokines. Obesity puts an organism into a chronic infl ammatory state. Th e correlation of obesity with the presence of proinfl ammatory interleukins such as IL-1 in adipose tissue is linked to insulin resistance, likely via direct crosstalk between IL-1 and insulin signaling pathways. Production and secretion by adipocytes of IL-6, another pro-infl ammatory interleukin, also correlate with obesity, but its functions in adipose tissue are more complex. Whereas short-term increase of IL-6 appears to have positive eff ects on fat oxidation and glucose transport, chronic exposure to elevated IL-6 induces insulin resistance similar to eff ects seen with high exposure to IL-1. Production and secretion by adipocytes of other pro-infl ammatory interleukins, IL-8 and IL-18, also correlate with obesity. Studies on mice genetically modifi ed to lack IL-18, however, show that IL-18 is important for maintaining normal weight. Th e production and secretion by adipocytes of the anti-infl ammatory interleukin, IL-10, are inversely correlated to obesity. Whereas few interleukins are adipokines, many interleukins have direct eff ects on adipose tissue.
