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Leptin is a peptide hormone synthesized by adipocytes. The main function of leptin is associated with regulation of the body energetic balance and restriction of excess accumulation of fat. This review considers in detail the involvement of leptin in regulation of fundamental effector functions of mononuclear phagocytes, which express receptors for this hormone. Possible molecular mechanisms of modulation by leptin of phagocytic activity, oxygen-dependent microbicidity, and nitric oxide generation by mononuclear phagocytes are analyzed, as well as the role of leptin in the formation of the produced cytokine pattern. The data presented suggest that the regulation of mononuclear phagocytes by leptin is associated with activation of the JAK/STAT signaling pathway, which leads to stimulation of phagocytosis, production of oxygen and nitrogen reactive species, and also to increase in secretion of pro-inflammatory cytokines.

We studied isolated and combined effects of leptin and ghrelin on the formation of IL-producing and T-regulatory cells. Leptin in concentrations comparable with its normal blood concentration during pregnancy (trimester II-III) promotes differentiation of peripheral blood CD4(+) cells to IL-17-producing cells and enhances IL-17A production, but suppresses the formation of T-regulatory cells in vitro. In contrast, ghrelin in a concentration typical of trimester I-II of pregnancy reduces the number of IL-17-producing cells, but stimulated the formation of T-regulatory cells. The effects of leptin and ghrelin in combination typical of trimester I-II of pregnancy stimulated the formation of T-regulatory cells, while in combination typical of trimester II-III did not shift the balance of T-regulatory cells and IL-17-producing cells, but stimulated the formation of IL-17A. We conclude that leptin and ghrelin play an important role in the maintenance of the balance of IL-17-producing and T-regulatory cells during pregnancy.

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Both leptin and ghrelin used separately at the concentrations corresponding to trimesters II-III of pregnancy increase the number of CD56 NK cells in mononuclear cell suspension; their combination also enhances the L-selectin expression on the surface of these cells in the culture. These hormones do not affect the production of TGF-β1, IL-17А, or IFN-γ by NK cells, and they inhibit the production of IL-10. Leptin decreses the IL-4 production by NKp46 cells, but the presence of ghrelin abrogates this effect.