Leptin and immune function: integrating the evidence

Leptin, an adipocyte-derived hormone that functions in the regulation of energy intake and body fat stores, may provide a possible connection between body fat and immune function. This review presents a summary of published research relating serum leptin concentrations to measures of inflammation and immune function. In vitro and animal studies suggest a multifunctional role of leptin in immune function, including associations with the proinflammatory TH1 response, natural killer cell cytotoxicity, C-reactive protein, IL-6, tumor necrosis factor α, and, possibly, with serum amyloid A. It is difficult to discern whether there are also direct effects of cytokines on leptin; yet, at least with respect to tumor necrosis factor α, some studies suggest such a link. To date, few clinical studies have examined the relationship between leptin and immune activity in humans, and the association between leptin and immune function in healthy individuals is not well established. Thus, the complex relationship between leptin and immune function in free-living humans remains a topic for future research.