Deficiency of neutrophil membrane antigen detected by monoclonal antibody in rheumatoid arthritis

Inhibition of neutrophil responses by cyclosporin A. An insight into molecular mechanisms

OBJECTIVE

Cyclosporin A (CsA) is an effective agent in rheumatoid arthritis (RA), slowing joint damage progression. Its therapeutic effect on T lymphocytes has been studied extensively, but there is little information available about neutrophils, the cells responsible for a substantial proportion of inflammation. A study was performed to investigate the in vitro effects of CsA on neutrophil functions triggered by several agonists and determine whether the drug could counteract the binding of formyl-methionyl-leucyl-phenylalanine (fMLP) to its receptor and/or modulate changes in the intracellular Ca(2+) concentration ([Ca(2+)]i).

METHODS

CsA was added to neutrophils 5-50 min before the incubation steps for neutrophil function assays (chemotaxis, superoxide anion production, lysozyme release), calcium measurements and receptor binding experiments.

RESULTS

CsA appeared to be particularly effective in lowering chemotaxis, superoxide anion production and lysozyme release induced by different agonists. However, it did not significantly affect either basal or agonist-stimulated neutrophil [Ca(2+)]i and the interaction between fMLP and its receptor.

CONCLUSIONS

Because of its in vitro inhibition of neutrophil functions, CsA appears to have considerable potential as an anti-inflammatory drug. Moreover, as it is also a potent immunosuppressive agent, it may reduce the progression of joint damage in RA. More work remains to be done to clarify the molecular mechanism of CsA action on neutrophils.

Neutrophils from patients with myelodysplastic syndromes: relationship between impairment of granular contents, complement receptors, functional activities and disease status

Myelodysplastic syndromes (MDS) are stem cell disorders of clonal origin in which infections and leukemic transformation are quite frequent. Neutrophils from 28 patients with MDS were analysed by flow cytometry for the expression of the two complement receptors CR1 and CR3, the antigenic reactivity of some granule constituents--myeloperoxidase, lysozyme, elastase, lactoferrin--and functional activities, such as locomotion, respiratory burst and cytotoxicity. The results were correlated with the FAB disease subtypes, grouped as low risk (RA) and high risk patients (RAEB, RAEB-t, CMML) and with 30 healthy subjects. A significant reduction in the percentage of neutrophil CR1, CR3 positivity and chemotaxis induced by endotoxin-activated serum was detected in the high risk group when compared with the low risk group and healthy controls. Furthermore, the high risk group also showed a low amount of myeloperoxidase, elastase, lysozyme and superoxide anion, but both low and high risk groups displayed reduced cellular cytotoxicity in comparison with the control. This work indicates that MDS patients belonging to the more advanced FAB categories frequently show multiple abnormalities in the expression of neutrophil complement receptors, and granular components (> 3), as well as in cell functions, suggesting the possibility of using these phenotypic abnormalities in the monitoring of disease progression.

Modulation of neutrophil functions by activated platelet release factors

Platelets activated with physiological agonists, such as thrombin, ADP, or collagen, released products able to modulate neutrophil functions. In particular, platelet supernatant contained an inhibitor of superoxide anion generation induced by phorbol ester and a chemotactic factor for human neutrophils. The proteolytic digestion of platelet supernatant completely abrogated chemotactic activity without interfering with the inhibitory effect, indicating the presence of different molecules involved in the modulation of different neutrophil functions. This was further confirmed by the pretreatment of platelets with aromatic benzamidine which abolished chemotactic activity, but did not affect superoxide inhibition of neutrophils. This report provides evidence for interaction of platelets and inflammatory cells, suggesting that platelets are able to induce accumulation of neutrophils and control their respiratory burst, which also has a critical role in tissue damaging in inflammation.

CD16 and CR3 receptors distinguish between the two mechanisms of tumour cytotoxicity in neutrophils

Previous studies have suggested that phorbol ester-activated neutrophils kill both antibody non-coated and antibody-coated K562 target cells. In this report the contribution of the receptors Fc gamma III (CD16) and CR3 (CD11b/CD18) in the lytic process was investigated. In neutrophils CD16 and CR3 are up-regulated by the phorbol ester up to 4 and 10 times, respectively. As expected, lysis of non-immunized K562 targets is not affected by the treatment of neutrophils with anti CD16, AB8.28, whereas lysis of immunized targets is decreased by 50%. In addition, the interaction of CD16 and AB8.28 induces calcium mobilization and increases granule secretion. Surprisingly, the simultaneous binding of AB8.28 and anti-CR3 OKM1 to neutrophils completely abolishes the lysis of antibody-coated targets. Unlike CD16, CR3 does not possess a functional role and binding of OKM1 to CR3 does not affect cytotoxicity of immunized K562 targets, but it blocks lysis of non-coated target almost completely, indicating a function as adhesion protein for CR3. These studies demonstrate a distinct role of CD16 and CR3 in mediating antibody-dependent and antibody-independent cellular cytotoxicity, respectively.

Dual mechanism in induction of human neutrophil cytotoxicity: activation of protein kinase C and elevation in intracellular calcium

Human neutrophils can damage the non-immunized K562 cell line when stimulated by phorbol myristate acetate (PMA). The combination of the activation of protein kinase C by phorbol and the increase of free intracellular calcium by ionophore potentiates the lytic reaction. The OKT9-immunized target cells are not able to induce by themselves the lytic response in neutrophils, but by combining the two signals, the antigenic stimulus and PMA, a high level of cytolytic response is attained. The addition of EGTA does not affect neutrophil cytotoxicity against antibody-coated targets, while it markedly reduced the lytic reaction against non-immunized targets; in contrast, the addition of EGTA together with the ionophore ionomycin completely suppresses the lysis of immunized and non-immunized targets. The treatment of neutrophils with the protein kinase C inhibitor H-7 causes a dose-related inhibition of the lytic functions that is greater on unsensitized K562. Thus the interaction of Fc receptors with immunized targets is required for reaching the maximal cytolysis. The enhanced lytic activity that occurs in the presence of immunized targets is mediated by calcium flux, as detected by using the monoclonal antibody AB8.28 which binds to FcIII receptors (FcRIII), thus supporting that both signals are involved.

Triggering of neutrophil cytotoxicity against an antibody-coated tumour target by TPA

The human erythroid myeloid leukaemia cell line K562 was used as target for human neutrophil cytotoxicity. Neutrophils demonstrated cytotoxicity against K562 only in the presence of a second stimulus, tetradecanoyl phorbol acetate (TPA), a result consistent with previous observations. We now demonstrate that antibody-coated K562 (using OKT9 and 345 monoclonal antibodies) are similarly only sensitive to neutrophils when TPA is added. The presence of both antibody and TPA in the cytotoxic assay resulted in significantly higher levels of cytotoxicity than in the absence of antibody; the result being consistent with a synergistic action between protein kinase C activation and Fc receptor perturbation in the neutrophil. The cytotoxicity against non-coated and antibody-coated targets was markedly inhibited, particularly against the former, by the protein kinase C inhibitor, 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine (H-7). There were marked differences in the extracellular calcium dependency of the two types of cytotoxicity reactions. TPA-activated respiratory burst was unaffected by the presence of non-coated and OKT9-coated targets, whereas TPA-induced lysosomal enzyme release was significantly increased by non-coated targets and a further increase occurred in the presence of OKT9-coated K562.

Protein kinase C mediates human neutrophil cytotoxicity

Human neutrophils stimulated with phorbol myristate acetate were able to damage human erythroleukemic K562 cells, in the absence of specific antibody, as assessed by a two hour 51Cr release assay. Neutrophils treated with formyl-peptide fMet-Leu-Phe did not display tumoricidal response, but the addition of diacylglycerol kinase inhibitor R59022 together with formyl-peptide induced the cytotoxic capacity against tumor target cells. Phorbol ester is a potent activator of certain functions of neutrophils because of its ability to directly and irreversibly stimulate protein kinase C; formyl-peptide, on the contrary, activates protein kinase C by inducing a rapid and transient production of diacylglycerol, that is quickly metabolized. The addition of an inhibitor of diacylglycerol kinase, R59022, however potentiated the action of formyl-peptide. These results indicate that protein kinase C is involved in the tumoricidal activity of neutrophils against K562 cells, and that maximal activation of the enzyme is required to achieve the cytotoxic response.