Adipocytes produce hormones and adipokines, among others leptin, with metabolic and inflammatory responses. The role of leptin involves different subsets of the immune system. Low levels of serum leptin concentrations are associated with bacterial infections and produce susceptibility to allergic diseases and type Th2 autoimmune diseases. High levels of leptin are associated with Th1 autoimmune diseases via inflammatory responses. Leptin resistance, that happens in obesity, is characterized by the presence of high levels of serum leptin itself accompanied by a clinical situation of a Th2 response. There is a relationship between obesity, leptin resistance, altered immunity and sex hormones. Serum leptin concentration (Th1 response) in women is higher than in men maybe to achieve the balance Th1/Th2 because of the high level of estrogenic hormones (Th2 response) in women.