Leptin, 16 kDa protein and the product of the Ob gene was discovered six years ago and characterized as a fat cell hormone which maintains via specific receptors in the hypothalamus by a feedback mechanism the energy balance and body weight. Research conducted during the last three years detected further properties of this protein which include it, in addition to its basic role in mammalian metabolism, also among acute phase reactants. Leptin is as to its structure, pattern of the receptor and the postreceptor transduction mechanism close to the group of cytokines of interleukin 6, in particular the granulocytic colony stimulating factor. During infectious and non-infectious inflammatory reactions leptin synthesis is stimulated by a combination of inflammation promoting cytokines. The mechanism of induction is not known so far but the majority of investigations proves an indirect stimulating effect of the tumour necrosis factor and interleukin 1, depending on nonspecified cytokines of the second stage. Investigations of cell lines and animal experiments provided evidence of some local and systemic effects of leptin which may play a physiological part in the acute phase reaction. Leptin mediates at least partly the anorectic effect of the tumour necrosis factor and interleukin 1 during inflammation.Synergically with bacterial antigens it activates macrophages, enhances their phagocytic capacity and stimulates secretion of pro- and antinflammatory factors from macrophages. Leptin stimulates neovascularization, it has a stimulating effect on precursors of white blood cells and potentiates the effect of erythropoietin on red blood cells. It is obviously an essential factor for T-lymphocyte proliferation and development. The authors discuss also the role of leptin in the modulation of the hypothalamo-pituito-adrenal stress axis. Leptin is a factor of the inflammatory mediator network, probably essential for an adequate course of the inflammatory defence reaction.

        Key words: Cytokines - Cortisol - Leptin - Acute phase reaction