Priming of human neutrophil functions by tumor necrosis factor: enhancement of superoxide anion generation, degranulation, and chemotaxis to chemoattractants C5a and F-Met-Leu-Phe

Physiology and pathophysiology of complement: progress and trends

The complement system comprises a family of at least 20 plasma and membrane proteins that interact in a tightly regulated cascade system to destroy invading bacteria and prevent the deposition of immune complexes in the tissues. This brief review addresses the basic mechanisms of complement activation and control and describes the active fragments produced during complement activation. The biological importance of the complement system is amply illustrated in patients with complement deficiencies, who are susceptible to bacterial infections and immune complex diseases. The involvement of complement in other immunological diseases is an expanding area of clinical research, supported by the development of new assays for the identification of complement activation. This area is discussed here with particular reference to neurological diseases. A promising new prospect involves the use of complement inhibitory molecules in therapy of complement-mediated disease and this exciting area is also discussed. Novel physiological roles of complement also are being revealed and new evidence that complement and complement receptors play an important role in reproduction is summarized. It is hoped that this brief overview will convey some of the enthusiasm currently pervading research in this underappreciated area of immunology.

CoA-independent transacylase activity is increased in human neutrophils after treatment with tumor necrosis factor alpha

CoA-independent transacylase (CoA-IT) appears to play a critical role in lipid mediator generation by rapidly moving arachidonate (AA) between phospholipid pools during cell activation. Tumor necrosis factor-alpha (TNF) pretreatment of human neutrophils increases agonist-induced production of inflammatory mediators. The current study tested if the TNF-induced increase in lipid mediator production may be, in part, due to altered CoA-IT activity. Neutrophils were treated with TNF (250 U/ml, 30 min), homogenates prepared, and CoA-IT activity measured by the ability of these homogenates to acylate 1-[3H]alkyl-2-lyso-sn-glycero-3-phosphocholine (GPC). There was an increased CoA-IT activity, from 9.1 +/- 1.1 to 13.7 +/- 1.4 pmol/mg per min in control vs. TNF-treated samples, respectively. Varying the concentration of 1-alkyl-2-lyso-GPC revealed an increased CoA-IT activity in microsomes that was due to an increased Vmax, from 26 to 54 pmol/mg per min. The ability of TNF to increase CoA-IT activity was concentration-dependent, with maximal response observed at 25 U/ml. This effect on CoA-IT appears to be specific, in that TNF treatment of neutrophils had no effect on CoA-dependent acylation of 1-acyl-2-lyso-sn-glycero-3-phosphocholine, using either AA-CoA or linolenoyl-CoA as substrates. In the intact cell, the movement of [3H]AA from other phospholipids into PE in fMLP-stimulated neutrophils was greatly enhanced after TNF treatment, demonstrating a functional consequence of increased CoA-IT activity. In addition, TNF treatment doubled platelet-activating factor production in response to the chemotactic peptide fMLP, as measured by [3H]acetate incorporation, while the response to A23187 remained unchanged. Taken together, these results provide the first evidence of modulation of CoA-IT activity by a proinflammatory cytokine and suggest that one mechanism for augmented lipid mediator formation is through increases in CoA-IT activity.

Migratory activity of blood polymorphonuclear leukocytes during juvenile rheumatoid arthritis, demonstrated with a new whole-blood membrane filter assay

Polymorphonuclear leukocyte (PMN) migration is measured in whole blood in a migration chamber consisting of a membrane filter (3-microns pores, 140 microns thick) with an integrated chemoattractant depot (FMLP in solid form) attached to a plastic container. Control chambers lack FMLP (blanks). One test unit requires 300 microliters blood. Numbers and distribution of the PMN immigrants into the filters are determined microscopically. Altogether 26 measurements of PMN migration in five juvenile rheumatoid arthritis (JRA) patients with varying disease activity were compared with the reactions of a healthy control group (N = 32). Correlations were calculated with conventional laboratory parameters (WBC, PLT, BSR, CRP, Hgb, serum Fe) and disease activity. In comparison with healthy controls, PMNs of JRA patients generally show a markedly increased penetration depth into the filters irrespective the presence of the chemoattractant or the disease activity. Increased migratory reactions to FMLP in comparison to blanks were found during high disease activity only. The PMN penetration depth correlates positively with the CRP, and reciprocally with the Hgb blood levels. The migration assay combines fast and simple processing with good preservation of the genuine PMN activation state.

Tumor necrosis factor-alpha as a myocardial depressant substance

Most patient with sepsis and septic shock develop significant derangements of myocardial function. The presence of a circulating myocardial depressant substance (MDS) has been suggested to be the major cause of myocardial depression in sepsis and septic shock. MDS is still not fully characterized by chemical means, and there is no consensus regarding its identity. Nevertheless, high levels of MDS activity can be found in sera from patients with sepsis and septic shock. Furthermore, MDS has been shown to have a number of specific characteristics. These characteristics have also been described with tumor necrosis factor-alpha (TNF), a cytokine that is well recognized to be a primary mediator in the pathogenesis of infection, tissue injury, inflammation and shock. In this review it is suggested that TNF is an MDS, and that the cardiovascular injury and myocardial depression during sepsis and septic shock involve a final common pathway, where TNF may have an important role in this common pathway.

The effect of cytokines on bactericidal activity of murine neutrophils

A range of recombinant cytokines have now been shown to modify aspects of the phenotype and function of human and murine neutrophils. However, few reports describe modification of the bactericidal activity of neutrophils. We therefore examined the recombinant murine cytokines tumor necrosis factor-alpha (TNF-alpha, 10-1000 ng ml-1) and granulocyte macrophage-colony stimulating factor (GM-CSF, 10-1000 U ml-1) for their ability to increase the bacterial killing capacity of murine neutrophils. Neutrophils from either bone marrow (fresh or cultured), or peritoneal exudates, or abscesses, were pre-incubated with either cytokine for 30-60 min and the killing of Proteus mirabilis, Escherichia coli, or Bacteroides fragilis was examined in the presence or absence of serum over a 90 min period. Only for one combination was a small but significantly enhanced level of bacterial killing observed, the phagocytic killing of P. mirabilis by peritoneal exudate neutrophils in the presence of GM-CSF and serum. With this exception there was no enhancement of bacterial killing for the range of combinations of neutrophils and bacterial species tested. In contrast, at the concentrations tested for effect on bactericidal activity, TNF-alpha and GM-CSF were able to significantly upregulate CR3 (but not Fc gamma RII) expression on mouse neutrophils. These results indicate that upregulation of CR3 as an index of neutrophil activation does not necessarily correlate with increased bactericidal activity.

Effects of clofazimine analogues and tumor necrosis factor-alpha individually and in combination on human polymorphonuclear leukocyte functions in vitro

In the present study the individual and interactive effects of clofazimine, or three analogues of this agent (selected on the basis of similar or superior pro-oxidative properties: B669, B746 and B4021) and human recombinant TNF-alpha on the generation of antimicrobial oxidants by human polymorphonuclear leukocytes (PMNL), as well as release of granule enzymes from these cells, were investigated in vitro. All four riminophenazines at the concentrations tested (0.5 and 1.0 micrograms/ml) significantly increased myeloperoxidase (MPO)-mediated iodination, superoxide (0(2).-) generation, oxygen (0(2)) consumption and chemiluminescence (CL), as well as the release of both primary and secondary granule contents (measured as the release of MPO, lysozyme and vitamin B12-binding protein) by stimulated PMNL. Similar, but less impressive effects were observed with TNF-alpha (0.4-50.0 ng/ml). When PMNL were preincubated with both TNF-alpha and clofazimine or its analogues, the observed stimulation of cellular oxidative metabolism and granule enzyme release was at least additive in many assays. These data demonstrate that the spectrum of effects of clofazimine and its analogues on PMNL closely resemble those of TNF-alpha. Furthermore, TNF-alpha potentiates the pro-oxidative effects of clofazimine and its analogues on PMNL. Among the riminophenazines tested, clofazimine and B669 appear to be the most potent pro-oxidative agents for PMNL.