Leptin, the adipocyte-secreted hormone, exerts its main function as regulator of 
food intake and energy expenditure through central effects at the hypothalamic 
level. However, it appeared that this cytokine-like peptide has also direct 
effects on other peripheral tissues and cell types. Remarkable effects have been 
demonstrated on the immune function in vivo and in vitro. Monocytes are one of 
the target cells of leptin, and we have demonstrated that secretion of L-1Ra, an 
IL-1 receptor antagonist, is induced by leptin. In human obesity leptin and 
IL-1Ra levels are elevated, and these levels are decreased after weight loss. It 
is discussed that IL-1Ra may contribute to central leptin resistance.