Abstract. Leptin is a pleiotropic molecule involved in energy homeostasis, hematopoiesis, inflammation, and immunity. Hypoleptinemia characterizing starvation has been strictly related to increased susceptibility to infection secondary to malnutrition. Nevertheless, ESRD is characterized by high susceptibility to bacterial infection despite hyperleptinemia. Defects in neutrophils play a crucial role in the infectious morbidity, and several uremic toxins that are capable of depressing neutrophil functions have been identified. Only a few and contrasting reports about leptin and neutrophils are available. This study provides evidence that leptin inhibits neutrophil migration in response to classical chemoattractants. Moreover, serum from patients with ESRD inhibits migration of normal neutrophils in response to N-formyl-methionyl-leucyl-phenylalanine with a strict correlation between serum leptin levels and serum ability to suppress neutrophil locomotion.Finally, the serum inhibitory activity can be effectively prevented by immune depletion of leptin. The results also show, however, that leptin by itself is endowed with chemotactic activity toward neutrophils. The two activities-inhibition of the cell response to chemokines and stimulation of neutrophil migration-could be detected at similar concentrations. On the contrary, neutrophils exposed to leptin did not display detectable [Ca 2ϩ

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The lysis of tumor cells, and other nucleated mammalian cells, by neutrophilic polymorphonuclear leukocytes (PMNs) triggered by phorbol myristate acetate (PMA) represents a widely used model system to dissect the PMN cytolytic armamentarium, potentially responsible for the cell damage at tissue sites of PMN activation. Although oxidants are generally considered to be instrumental in the target lysis by PMNs, the mediators actually involved remain a matter of controversy. Moreover, other factors potentially crucial to the lysis have not been clearly identified. In order to reexamine the determinants of the cytolytic process, we studied the events underlying the PMA-triggered PMN-delivered attack against two different targets, selected on the basis of preliminary experiments (B lymphoblastoid Daudi cells and erythroleukemic K 562 cells). The results suggest that the lysis is promoted by hypochlorous acid (HOCl) or a compound with characteristics very similar to HOCl itself. No evidence was obtained for the intervention or contribution of hydrogen peroxide (H2O2), hydroxyl (OH.) radicals, and the major HOCl-derived chloramines. PMNs appeared to use 35% of the generated H2O2 to produce HOCl, while the remainder appears to be consumed by PMNs themselves and target cells as well. Moreover, PMNs and target cells coaggregated at an early step of the cytolytic reaction, through a process efficiently prevented by a monoclonal antibody (MoAb J-90) directed against leukocyte function-associated antigen-1 (LFA-1). The inhibition of the PMN-target aggregation by the MoAb J-90 resulted in the impairment of the lysis, despite a normal generation of HOCl. Thus, the data demonstrate that the PMA-triggered lysis of tumor target cells by PMNs requires at least two events, occurring simultaneously: the LFA-1-mediated effector-target adherence and the PMN production of HOCl. The intervention of the LFA-1-mediated PMN-target adherence in the PMA-triggered lysis is likely to allow PMNs to focus HOCl on the target cell surface and suggests that the process requires a sort of molecule to molecule recognition at the effector-target surface level.

1. It is well known that neutrophils act as mediators of tissue injury in a variety of inflammatory diseases. Their histotoxic activity is presently thought to involve proteinases and oxidants, primarily hypochlorous acid (HOCl). This oxidant is also capable of inactivating the specific inhibitor of neutrophil elastase (alpha 1-antitrypsin), thereby favouring digestion of the connective matrix. 2. In the present work, we found that sulphanilamide and some sulphanilamide-related anti-inflammatory drugs such as dapsone, nimesulide and sulphapyridine reduce the availability of HOCl in the extracellular microenvironment of activated neutrophils and prevent the inactivation of alpha 1-antitrypsin by these cells in a dose-dependent manner. The ability of each drug to prevent alpha 1-antitrypsin from inactivation by neutrophils correlates significantly with its capacity to reduce the recovery of HOCl from neutrophils. Five other non-steroidal anti-inflammatory drugs were completely ineffective. 3. Therefore, sulphanilamide-related drugs, i.e. dapsone, nimesulide and sulphapyridine, have the potential to reduce the bioavailability of neutrophil-derived HOCl and, in turn, to favour the alpha 1-antitrypsin-dependent control of neutrophil elastolytic activity. These drugs appear as a well-defined group of agents which are particularly prone to attenuate neutrophil histotoxicity. They can also be viewed as a previously unrecognized starting point for the development of new compounds in order to plan rational therapeutic strategies for controlling tissue injury during neutrophilic inflammation.

Monocytes and macrophages play a key role in the initiation and persistence of inflammatory reactions. The possibility to interfere with the survival of these cells, once recruited and activated at sites of inflammation, is an attractive therapeutic option. Although resting monocytes are susceptible to pharmacologically induced apoptosis, no data are available about the possibility to modulate the survival of activated monocytes. The present work was planned to investigate if dexamethasone is able to promote apoptosis of human monocytes activated by immune complexes. When monocytes were cultured with immune complexes, a dose-dependent inhibition of apoptosis was observed. Dexamethasone stimulated apoptosis of resting and activated monocytes in a dose-dependent manner. Both the immune complex inhibitory activity and dexamethasone stimulatory properties depend on NF-kappaB/XIAP and Ras/MEK/ERK/CD95 pathways. In fact, the exposure of monocytes to immune complexes increased NF-kB activation and XIAP expression, which in turn were inhibited by dexamethasone. On the other hand, immune complex-stimulated monocytes displayed a reduced expression of CD95, which is prevented by dexamethasone, as well as by MEK inhibitor U0126. Furthermore, anti-CD95 ZB4 mAb prevented dexamethasone-induced apoptosis in immune complex stimulated monocytes. Similarly, ZB4 inhibited dexamethasone-mediated augmentation of caspase 3 activity. The present findings suggest that Fc triggering by insoluble immune complexes result in the activation of two intracellular pathways crucial for the survival of monocytes: 1. Ras/MEK/ERK pathway responsible for the down-regulation of CD95 expression; 2. NF-kappaB pathway governing the expression of XIAP. Both the pathways are susceptible to inhibition by monocyte treatment with pharmacologic concentrations of dexamethasone.