The past few years of research on leptin have provided important information on the link between metabolism and immune homeostasis. Adipocytes influence not only the endocrine system but also the immune response through several cytokine-like mediators known as adipokines, which include leptin. It is widely accepted that leptin can directly link nutritional status and pro-inflammatory T helper 1 immune responses, and that a decrease of leptin plasma concentration during food deprivation can lead to an impaired immune function. Additionally, several studies have implicated leptin in the pathogenesis of chronic inflammation, and the elevated circulating leptin levels in obesity appear to contribute to the low-grade inflammatory background which makes obese individuals more susceptible to increased risk of developing cardiovascular diseases, type II diabetes, or degenerative disease including autoimmunity and cancer. Conversely, reduced levels of leptin such as those found in malnourished individuals have been linked to increased risk of infection and reduced cell-mediated immune responses. We discuss here the functional influences of leptin in the physiopathology of inflammation, and the effects of leptin in the modulation of such responses.

Natural killer (NK) cells of the innate immune system can profoundly impact the development of adaptive immune responses. Inflammatory and autoimmune responses in anatomical locations such as the central nervous system (CNS) differ substantially from those found in peripheral organs. We show in a mouse model of multiple sclerosis that NK cell enrichment results in disease amelioration, whereas selective blockade of NK cell homing to the CNS results in disease exacerbation. Importantly, the effects of NK cells on CNS pathology were dependent on the activity of CNS-resident, but not peripheral, NK cells. This activity of CNS-resident NK cells involved interactions with microglia and suppression of myelin-reactive Th17 cells. Our studies suggest an organ-specific activity of NK cells on the magnitude of CNS inflammation, providing potential new targets for therapeutic intervention.

In systemic lupus erythematosus (SLE), adaptive CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) suppress Th cells that help autoantibody (autoAb)-producing B cells. It is not known whether naturally occurring Tregs can directly suppress B cells in SLE without an intermediate suppression of Th cells. This aspect is important for its implications in the natural course of SLE, because most if not all of the clinical and pathologic effects in SLE are associated with a dysregulated production of autoAbs. In this study, we show that natural Tregs can inhibit B cell activity in vitro and in vivo in SLE through cell contact-mediated mechanisms that directly suppress autoAb-producing B cells, including those B cells that increase numerically during active disease. These results indicate that one way by which natural Tregs attempt to limit humoral autoimmunity in SLE is by directly targeting autoreactive B cells.