Leptin and adiponectin: from energy and metabolic dysbalance to inflammation and autoimmunity

There is a growing evidence that both overnutrition and undernutrition negatively interfere with immune system. The overnutrition has been found to increase susceptibility to the development of inflammatory or autoimmune diseases. On the other hand, starvation or malnutrition has been more associated with increased susceptibility to infections. In the regulation of immune and inflammatory processes, white adipose tissue plays a critical role as an endocrine organ which produces number of active peptides, called adipokines. The adipokines, leptin and adiponectin represent a critical link among nutritional status, metabolism and immunity. Leptin is primarily known as a satiety factor regulating body weight by suppression of appetite and stimulation of energy expenditure, and its serum levels and gene expression in adipocytes strongly correlate with proportion of body fat stores. On the other hand, leptin is a pro-inflammatory adipokine inducing T helper 1 cells and may contribute to the development and progression of autoimmune responses. Adiponectin plays an important role as an insulin-sensitizing adipokine which production is decreased in obesity and in conditions associated with insulin resistance. Adiponectin also acts as an anti-inflammatory factor especially with regard to atherosclerosis, but in some chronic inflammatory/autoimmune diseases adiponectin may have pro-inflammatory effects and its production correlates with inflammatory markers and disease activity. This review discusses the main biological activities of leptin and adiponectin as well as their contribution to inflammatory and autoimmune processes with particular focus on rheumatoid arthritis and its experimental models.