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Augmentation of neutrophil-mediated erythrocyte lysis by cells derived in vitro from human monocytes
F Dallegri1, A Ballestrero, G Frumento
1First Medical Clinic, University of Genoa Medical School, Italy.
Abstract:
Neutrophilic polymorphonuclear leukocytes (PMNs) were incubated with opsonized zymosan and lysed human erythrocytes (RBCs) as measured by a 51Cr release method. Conversely, myeloperoxidase (MPO)-negative hydrogen peroxide (H2O2)-generating cells, derived in vitro from human monocytes (monocyte-derived cells (MDCs), were ineffective per se but capable of augmenting the lysis by PMNs. The lysis by PMNs and PMNs plus MDCs was inhibited by catalase, azide, taurine, and alanine, consistent with the requirement for hypochlorous acid (HOCl). As detected under conditions similar to those used for lytic assays, MDCs failed to produce HOCl but augmented the HOCl recovery from the PMN-RBC system. Moreover, when the extent of the lysis was plotted as a function of the HOCl recovery, a positive linear relationship was found. Although the actual size of the H2O2 extracellular pool could not be measured because of the inexistence of a reliable assay to probe our cytolytic model without perturbing the equilibrium of the system, the results presented suggest that MDCs enhance the PMN-mediated lysis by improving the HOCl production, presumably by supplying extra amounts of H2O2 to be handled by PMN MPO. In fact, the events mediated by MDCs could be reproduced by using an appropriate H2O2-generating enzymatic system (glucose-glucose oxidase). The present study provides direct evidence for the possibility of cooperation between MPO-positive and MPO-negative phagocytes in exerting functions (HOCl production and, in turn, cytolysis) possibly relevant to the outcome of inflammatory processes.
Insights
Monocyte-derived cells (MDCs) enhance neutrophil (PMN) lysis of red blood cells by boosting hypochlorous acid (HOCl) production. This suggests a cooperative role for different phagocytes in inflammation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Neutrophilic polymorphonuclear leukocytes (PMNs) are key phagocytes in inflammatory responses.
- Hypochlorous acid (HOCl), produced by PMN myeloperoxidase (MPO), is a potent antimicrobial agent.
- The role of MPO-negative cells in modulating PMN-mediated functions is not fully understood.
Purpose of the Study:
- To investigate the cooperative effect of MPO-negative monocyte-derived cells (MDCs) on PMN-mediated cytolysis.
- To elucidate the mechanism by which MDCs augment PMN function, specifically HOCl production.
Main Methods:
- Human erythrocytes (RBCs) and opsonized zymosan were used as targets for PMN-mediated lysis.
- 51Cr release assay measured RBC lysis.
- HOCl production was assessed in parallel with lytic assays.
- MDCs were used in combination with PMNs to study synergistic effects.
- Catalase, azide, taurine, and alanine were used to inhibit HOCl activity.
Main Results:
- MDCs alone did not lyse RBCs but augmented lysis mediated by PMNs.
- The augmentation of lysis by PMNs and MDCs was inhibited by agents that neutralize HOCl.
- MDCs did not produce HOCl but increased HOCl recovery in the PMN-RBC system.
- A positive linear relationship was observed between RBC lysis and HOCl recovery.
- H2O2-generating systems mimicked the effect of MDCs, suggesting H2O2 supply is key.
Conclusions:
- MDCs enhance PMN-mediated cytolysis by increasing HOCl production, likely through supplying hydrogen peroxide (H2O2).
- This study provides evidence for functional cooperation between MPO-positive (PMNs) and MPO-negative (MDCs) phagocytes.
- This phagocyte cooperation may be significant in the context of inflammatory processes.