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Leptin is a protein hormone structurally similar to interleukin 2, which regulates food intake and metabolic and endocrine function.1 It also has an important regulatory role in the immune response, mainly acting as a T cell growth factor.2 Moreover, it also effects cytokine production, monocyte/macrophage activation, wound healing, angiogenesis, and haemopoiesis.1 Leptin concentrations rapidly increase during infection and inflammation. The low concentrations of leptin that can occur during starvation or malnutrition are associated with impaired cellular immunity, impaired delayed-type hypersensitivity responses, and thymic atrophy, and thereby contribute to increased susceptibility to infection.2
High leptin concentrations are seen in obese and diabetic individuals, with the concentrations of leptin rising with increasing insulin resistance.3 However, despite high leptin concentrations, these individuals have leptin resistance or defective leptin.4 Therefore, leptin resistance, along with many other factors, may also contribute to the increased incidence of infection seen among patients with diabetes, who are more susceptible to infections such as tuberculosis and candidiasis, which require a good cellular immune response to overcome infection. Because leptin is important in the regulation of cellular immune responses, leptin resistance may be a contributing factor for the high incidence of such infections. Therefore, the role of leptin in infections in patients with diabetes should be further examined.