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The high-affinity Fc gamma RI on PMN: regulation of expression and signal transduction
F Hoffmeyer1, K Witte, R E Schmidt
1Division of Clinical Immunology, Hannover Medical School, Germany.
Abstract:
In this paper we report that interferon-gamma (IFN-gamma) maintains and enhances functional properties of terminally differentiated polymorphonuclear cells (PMN). Such effects are obvious when compared with untreated PMN declining in their functional response. Culture for 18 hr with 100 IU/ml of recombinant IFN-gamma resulted in the expression of about 15,000 Fc gamma RI per PMN. IFN-gamma maintained viability of PMN and prevented reduction of Fc gamma RIIIb caused by apoptosis. No alterations were found in the level of Fc gamma RIIa. Next, functional properties of Fc gamma RI were evaluated. Calcium mobilization was detected in fura-2/acetoxymethylester (AM)-loaded PMN using a spectrophotometer and the respiratory burst was measured as luminol-dependent chemiluminescence. Cross-linking of an F(ab')2 fragment of monoclonal antibody (mAb) 22.2 to Fc gamma RI gave similar results to those obtained with intact monomeric human immunoglobulin G (mhIgG) when subsequently cross-linked. Moreover, after blocking Fc gamma RIIa and Fc gamma RIIIb with respective mAb fragments, mhIgG was still effective in triggering a calcium flux demonstrating that second messenger generation was caused by Fc gamma RI engagement. Even though Fc gamma RI expression was lower than that of Fc gamma RIIa, Fc gamma RI induced a higher increase of the respiratory burst. In addition, the protein tyrosine phosphatase CD45 was able to inhibit both responses when it was co-cross-linked with CD64, suggesting involvement of tyrosine phosphorylation in early signalling steps.
Insights
Interferon-gamma (IFN-gamma) enhances polymorphonuclear cell (PMN) function by increasing Fc gamma RI expression and activity. This cytokine treatment maintains PMN viability and improves their response to immune stimuli.
Area of Science:
- Immunology
- Cell Biology
Background:
- Terminally differentiated polymorphonuclear cells (PMN) exhibit declining functional properties over time.
- Interferon-gamma (IFN-gamma) is a cytokine with known immunomodulatory effects.
Purpose of the Study:
- To investigate the effects of IFN-gamma on PMN functional properties and Fc gamma receptor expression.
- To elucidate the role of Fc gamma RI in IFN-gamma-mediated PMN activation.
Main Methods:
- PMN cultures treated with recombinant IFN-gamma.
- Flow cytometry for Fc gamma receptor expression analysis (Fc gamma RI, Fc gamma RIIa, Fc gamma RIIIb).
- Measurement of calcium mobilization and respiratory burst (chemiluminescence) in response to Fc gamma receptor engagement.
Main Results:
- IFN-gamma treatment significantly increased Fc gamma RI expression on PMN.
- IFN-gamma maintained PMN viability and prevented Fc gamma RIIIb reduction.
- Fc gamma RI engagement, even at lower expression levels than Fc gamma RIIa, induced a robust respiratory burst and calcium mobilization.
- Tyrosine phosphorylation, modulated by CD45 and CD64, is involved in Fc gamma RI signaling.
Conclusions:
- IFN-gamma rejuvenates PMN by enhancing Fc gamma RI-mediated functions.
- Fc gamma RI plays a critical role in IFN-gamma-induced PMN activation and immune response.
- Targeting Fc gamma RI signaling could be a therapeutic strategy for inflammatory conditions involving PMNs.