Interferon-gamma affects protein kinase C activity in human neutrophils

Interferon-gamma activation of polymorphonuclear neutrophil function

As current research illuminates the dynamic interplay between the innate and acquired immune responses, the interaction and communication between these two arms has yet to be fully investigated. Polymorphonuclear neutrophils (PMNs) and interferon-gamma (IFN-gamma) are known critical components of innate and acquired immunity, respectively. However, recent studies have demonstrated that these two components are not entirely isolated. Treatment of PMNs with IFN-gamma elicits a variety of responses depending on stimuli and environmental conditions. These responses include increased oxidative burst, differential gene expression, and induction of antigen presentation. Many of these functions have been overlooked in PMNs, which have long been classified as terminal phagocytic cells incapable of protein synthesis. As this review reports, the old definition of the PMN is in need of an update, as these cells have demonstrated their ability to mediate the transition between the innate and acquired immune responses.

Fibronectin promotes calcium signaling by interferon-gamma in human neutrophils via G-protein and sphingosine kinase-dependent mechanisms

A common intracellular signal activating polymorphonuclear leukocytes (PMN) in inflammation is a change in cytosolic calcium concentration. Previously, we have shown that interferon-gamma (IFN-gamma) induces transient calcium signals in PMN, but only after intracellular calcium store depletion. Using a digital imaging system, we show that adhesion of PMN is critical for IFN-gamma-induced calcium signals, and with PMN attached to the optimal coating, the calcium signals are evoked even in presence of extracellular calcium, that is, non-depleted calcium stores. Adhesion to fibronectin, pure or extracted from plasma by gelatin, improved the IFN-gamma responses compared with serum, plasma, or vitronectin coats. In accordance with previous observations, IFN-gamma-induced calcium signals in fibronectin adherent cells were totally abolished by the G-protein inhibitor pertussis toxin and were also inhibited by the sphingosine kinase inhibitors dimethylsphingosine (DMS) and N-acetylsphingosine (N-Ac-Sp). PMN contact with fibronectin alone, measured in cells sedimenting onto a fibronectin-coated surface or by addition of fibronectin to glass-adherent cells, evoked transient calcium signals. However, PMN in suspension did not respond to the addition of fibronectin or arginine-glycine-aspartate (RGD). The fibronectin-induced calcium signals were also clearly depressed by pertussis toxin and by the sphingosine kinase inhibitors DMS, dihydrosphingosine (DHS), and N-Ac-Sp. When the product of sphingosine kinase activity, sphingosine 1-phosphate (S1-P), was added to the cells, similar calcium signals were induced, which were dependent on a pertussis toxin-sensitive G-protein activity. Finally, addition of S1-P to the cells prior to stimulation with IFN-gamma partly mimicked the priming effect of fibronectin. In conclusion, fibronectin contact evokes by itself a calcium signal in PMN and further promotes calcium signaling by IFN-gamma. We suggest that fibronectin might activate sphingosine kinase, and that the sphingosine 1-phosphate thereby generated induces a calcium signal via a G-protein-dependent mechanism. Apparently, sphingosine kinase activity is also involved in IFN-gamma induced calcium signals.

Priming effects of GM-CSF, IFN-gamma and TNF-alpha on human neutrophil inflammatory cytokine production

Identifying and evaluating the priming agents for cytokine release by neutrophils might be helpful in controlling the innate immune response of the host. In the present study we examined the role of granulocyte/macrophage colony-stimulating factor (GM-CSF), interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) as priming agents for interleukin (IL)-1beta, IL-6 and TNF-alpha production by stimulated neutrophils from control subjects and malignant melanoma patients. When the cells from controls and patients were preincubated with primer agents, opsonized zymosan-stimulated inflammatory cytokine production was enhanced. The major neutrophil-priming factor for IL-6 secretion by polymorphonuclear leukocytes (PMNs) in the control and patient groups was TNF-alpha. However, GM-CSF and IFN-gamma are also significant primers. GM-CSF priming was critical for the release of TNF-alpha from PMNs in control and melanoma patients. The ability of GM-CSF, IFN-gamma and TNF-alpha to serve as effective priming agents for inflammatory mediator production by PMNs revealed a new role for these cytokines in the innate immune response of the melanoma-bearing host.

Modulation of functional activities of chicken heterophils by recombinant chicken IFN-gamma

The objective of the present studies was to examine the in vitro effects of recombinant chicken interferon-gamma (rChIFN-gamma) on shape change, phagocytosis, and the oxidative/nonoxidative killing activities of day-old chicken heterophils. Heterophils (4 x 10(6)/ml) were incubated with various concentrations of recombinant ChIFN-gamma from both Escherichia coli and transfected Cos cells for 2 h at 39 degrees C. The incubation of the neonatal heterophils with rChIFN-gamma resulted in significantly greater numbers of cells with membrane shape change when compared with the mock-treated heterophils. Both Cos cell-derived and E. coli-derived ChIFN-gamma significantly increased (p < 0.01) the phagocytosis of opsonized or nonopsonized Salmonella enteritidis by the neonatal heterophils in a concentration-dependent manner. Incubation with ChIFN-gamma induced no direct stimulation of the respiratory burst by the chicken heterophils but did prime the heterophils for a significantly strengthened respiratory burst to subsequent stimulation with opsonized zymosan (OZ). Lastly, incubation of the heterophils with ChIFN-gamma primed the cells for a significant increase in the release of beta-D-glucuronidase following stimulation with OZ. These results show that neonatal avian heterophils can respond to cytokine modulation with enhanced functional competence, suggesting that ChIFN-gamma can enhance the immune competence of the innate defenses of chickens during the first week of life.

Interferon-gamma elicits a G-protein-dependent Ca2+ signal in human neutrophils after depletion of intracellular Ca2+ stores

Interferon-gamma (IFN-gamma) has multiple effects on Ca2+ signalling in polymorphonuclear neutrophils (PMNs), including evoked cytosolic Ca2+ transients, increased capacitative calcium influx and increased sequestration of Ca2+ in intracellular stores. The present study was conducted to elucidate the mechanism behind the Ca2+ transients. As observed before, the IFN-gamma-evoked Ca2+ signals were apparent when extracellular Ca2+ was removed. A new finding was that the proportion of responding cells and the extent of calcium release increased with increasing time in EGTA buffer. As assessed by N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated Ca2+ release, the intracellular stores were depleted during this incubation period, and the extent of depletion correlated well with the appearance of IFN-gamma-induced Ca2+ signals. This store dependence of the IFN-gamma-induced Ca2+ signals was confirmed by the appearance of IFN-gamma-evoked Ca2+ signals in the presence of extracellular Ca2+ after store depletion by thapsigargin. The appearance of IFN-gamma-mediated Ca2+-signals in the presence of EGTA indicates that IFN-gamma stimulates Ca2+ release from intracellular stores. This was confirmed by the inability of the calcium transportation blocker La3+ to abolish the IFN-gamma response and the total abrogation of the response by the phospholipase C inhibitor U73122. Although these latter results imply a role for inositol 1,4,5-trisphosphate(IP3) in IFN-gamma signalling, comparison of IFN-gamma-evoked responses with fMLP responses revealed clear differences that suggest different signal-transduction pathways. However, responses to fMLP and IFN-gamma were both depressed by pertussis toxin, and the IFN-gamma responses were, in addition, inhibited by the tyrosine kinase inhibitor genistein. Further evidence of the involvement of tyrosine kinase was a slight stimulatory effect of the protein tyrosine phosphatase inhibitor sodium orthovanadate. The PI-3K activity was of minor importance. In conclusion, we present evidence of a novel signal-transduction mechanism for IFN-gamma in PMNs, dependent on tyrosine kinase activity, a pertussis toxin-sensitive G protein and phospholipase C activity.

IFN-gamma induces calcium transients and increases the capacitative calcium entry in human neutrophils

We have previously reported that long-term priming of human polymorphonuclear neutrophilic granulocytes (PMN) with interferon-gamma (IFN-gamma) increased the fMLP-stimulated calcium influx. We now show that also after short-term incubation with IFN-gamma, PMN calcium metabolism is modulated. Single adherent cells in three different calcium-containing buffers (high, normal, and low [Ca2+]) were stimulated with the bacterial peptide fMLP or the Ca-ATPase inhibitor thapsigargin (Tg) after about 5 min preincubation with IFN-gamma. The results of this protocol indicated that IFN-gamma increases both calcium influx and calcium sequestration. Store dependent Ca2+ influx, directly measured on readdition of calcium to Tg-treated cells incubated in EGTA buffer, was significantly enhanced in IFN-gamma-treated cells. This effect of IFN-gamma was enhanced by the tyrosine kinase inhibitor herbimycin A. Strikingly, in low extracellular calcium concentrations, IFN-gamma induced calcium transients in 20%-60% of the cells. The proportion of PMN responding with Ca2+ transients increased with decreasing extracellular calcium concentration. Average lagtime from addition of IFN-gamma to a response that could be measured was 7.3 sec, and average increase in [Ca2+] above the basal level was 790 nM. These IFN-gamma-induced transients could not be depressed by herbimycin A. Thus, IFN-gamma can increase capacitative calcium influx, induce calcium transients, and possibly affect calcium sequestration in human PMN.