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In response to a variety of stimuli, e.g. pathogens, phagocytes release reactive oxygen species which are essential for bacterial killing and also potentiate inflammatory reactions. We have used flow cytometry measurements to study the priming process of phagocyte oxidative burst in whole blood, in order to avoid introducing artefacts due to the purification process and to stimulate the in vivo situation more closely. In these conditions, we examined the in vitro effects of proinflammatory cytokines (TNF-alpha, IL-1 alpha, IL-1 beta, IL-6, IL-8 and GM-CSF) on the PMN oxidative burst. We found that none of the cytokine tested directly activated the PMN oxidative burst. In contrast, TNF, GM-CSF and IL-8 strongly primed a subpopulation of PMN which produced large amounts of H2O2 in response to fMLP, suggesting that these cytokines may play a critical role in bactericidal killing in vivo. Furthermore, we reported a decreased H2O2 production by TNF or IL-8 primed PMN in HIV-infected patients. This impairment, which correlated with the clinical stage of the disease, could contribute to the increased susceptibility to bacterial infections in HIV-infected patients. In addition, we reported the case of a child with severe recurrent infections due to intracellular microorganisms which could be related to an impairment of the phagocyte priming process of the oxidative burst [corrected].

Resume La production de formes reactives de l'oxygene (explosion oxydative) par les polynucleaires neutrophiles (PN) stimules joue un role majeur dans la defense de l'organisme contre differents agents pathogenes essentiellement bacteriens et fungiques. Cette production est soumise a une regulation fine et precise, notamment par les cytokines. Nous avons etudie, par cytometrie en flux, l'effet des cytokines pro-inflammatoires sur l'explosion oxydative des PN dans le sang total afin deviter toute prestimulation des cellules liee aux methodes d'isolement. Nous avons ainsi montre qu'aucune des cytokines etudiees (IL-1α, IL-1β, TNFα, IL-6, IL-8, GM-CSF) ne declenche isolement l'explosion oxydative des PN. Par contre, le pretraitement des PN par le TNF, l'IL-8 ou le GM-CSF suivie de l'addition d'un formyl peptide derive des proteines bacteriennes, conduit a l'apparition d'une sous-population de PN produisant d'importantes quantites de peoxyde d'hydrogene (H2O2). Cette sous-population se caracterise par une augmentation de la liaison des formyl peptides a la surface des PN. Nous avons egalement mis en evidence l'existence d'interactions cooperatives entre le TNF, le GM-CSF et l'IL-8, utilises a des concentrations suboptimales dans l'induction de la sous-population hyper-reactive.

Cytokines such as IL-10, IL-4, IL-13 and TGF-beta play a major role in the regulation of immune responses and are considered as anti-inflammatory agents mainly due to their actions on monocytes. These cytokines are also known to participate in the regulation of PMN activities. However, few and contradictory results have been reported on their direct and priming effects on the PMN oxidative burst, which is essential for killing bacteria. We used a flow cytometry method to study the effects of these cytokines on the PMN oxidative burst; we also used whole blood to avoid PMN activation related to isolation procedures and in order to simulate the in vivo situation more closely. None of the cytokines tested had direct or priming effects on PMN H2O2 production. We also show for the first time that these cytokines do not modulate TNF priming of the PMN oxidative burst in response to N-formyl peptides (fMLP). These results show that the anti-bacterial activity of PMN, in terms of the PMN respiratory burst, is not down regulated by these anti-inflammatory cytokines in whole blood.

Polymorphonuclear neutrophils (PMN) are the most abundant immune cells in inflammatory gingival sites of patients with early onset periodontitis, localized juvenile periodontitis, and rapidly progressive periodontitis (RPP). In the latter, the large number of PMN in connective tissue may explain the marked gingival destruction. Because interleukin-8 (IL-8) is a potent PMN chemoattractant, we evaluated circulating levels and gingival mRNA expression of IL-8. We found high IL-8 plasma levels as well as strong IL-8 mRNA expression in both epithelial and connective gingival cells from patients with RPP. Moreover, the gingival PMN themselves contained IL-8 mRNA, suggesting an autoamplification of PMN recruitment and activation in the gingiva. We also measured the expression of adhesion molecules at the PMN surface as well as the oxidative burst in whole blood from 14 patients with RPP, using flow cytometry to avoid irrelevant stimulations and to analyze single cells. In RPP patients, resting PMN showed reduced L-selectin, Lewis x, and sialyl Lewis x antigen expression as well as increased H2O2 production. These modifications of PMN adhesion molecule expression, together with their increased basal oxidative burst and excessive IL-8 production, may contribute to the noxious inflammatory reaction, which may in turn be autopotentiated by PMN production of IL-8. In addition, PMN showed a lack of increased response (H2O2 production) to formyl peptides after ex vivo priming with IL-8, possibly owing to IL-8 desensitization that may be involved in the increased susceptibility of RPP patients to infection. After appropriate treatment of RPP, the reduction in inflammation was associated with a return to control levels of both plasma IL-8 and PMN functions, suggesting that these features are linked.

We used flow cytometry to study the effects of pentoxifylline (PTX) on the expression of adhesion molecules and fMLP receptors on whole-blood polymorphonuclear neutrophils (PMN) in response to TNF, together with the oxidative burst and actin polymerisation. This technique analyses cells individually and avoids PMN activation related to isolation procedures. PTX reduced CD11b upregulation induced by TNF. Moreover, PTX reduced both TNF-induced binding of bacterial formyl peptides (fMLP) by human PMN and TNF priming of the PMN oxidative burst in response to these peptides. PTX also reduced TNF-induced actin polymerisation, which has been reported to participate in receptor cycling. This phenomenon could account in part for the ability of PTX to reduce fMLP binding to the PMN surface and subsequently to inhibit the PMN oxidative burst in response to fMLP. In addition to the PTX-induced decrease of TNF production, these effects on PMN could be beneficial in pathological conditions where high TNF production may induce excessive PMN activation, leading to vascular damage and tissue injury.

Impaired polymorphonuclear neutrophil (PMN) function may contribute to the onset of certain life-threatening bacterial and fungal infections in human immunodeficiency virus (HIV)-infected patients. Published data on PMN functional activity in HIV infection are controversial, possibly because most studies have involved PMNs isolated from their blood environment by means of various procedures that may differently affect surface receptor expression and thereby alter cellular responses. We therefore used flow cytometry to study the expression of adhesion molecules at the PMN surface, actin polymerization, and the oxidative burst of whole-blood polymorphonuclear neutrophils in 42 HIV-infected patients at different stages of the disease. These PMNs were activated in vivo, as demonstrated by increased expression of the adhesion molecule CD11b/CD18, reduced L-selectin antigen expression, increased actin polymerization, and increased H2O2 production. The alterations were present in asymptomatic patients with CD4+ cell counts greater than 500/microL and did not increase with the progression of the disease. Stimulation by bacterial N-formyl peptides showed dysregulation of L-selectin shedding and decreased H2O2 production after ex vivo priming with tumor necrosis factor alpha or interleukin-8 (IL-8). These latter impairments, which correlated with the decrease in CD4+ lymphocyte numbers and with IL-8 and IL-6 plasma levels, could contribute to the increased susceptibility of HIV-infected patients to bacterial infections.