Dissociation of neutrophil aggregation, adhesiveness, and Fc receptor activity

IL8 and PMA Trigger the Regulation of Different Biological Processes in Granulocyte Activation

The molecular mechanisms driving specific regulation of neutrophils are not completely understood to date. In order to characterize fundamental granulocyte features on protein level, we analyzed changes in proteome composition as reaction to stress from cell activation processes. For this purpose, we isolated primary granulocytes from equine whole blood through density gradient centrifugation followed by sodium chloride lysis and stimulated cells for 30 min with interleukin-8 (IL8) due to its role as a chemotactic factor for neutrophils. We additionally used phorbol 12-myristate 13-acetate (PMA) and lipopolysaccharide (LPS), which are primarily associated to neutrophil extracellular trap formation and release of reactive oxygen species. From mass spectrometry analysis, we identified a total of 2,032 proteins describing the whole granulocyte proteome, including 245 proteins (12% of identified proteome) newly associated to in vivo expression in primary equine granulocytes (hypothetical proteins). We also found distinct and different changes in protein abundance (ratio ≥ 2) after short stimulation of cells with various stimuli, pointing to rapid and differentiated reaction pattern. IL8 stimulation resulted in increased protein abundance of 58 proteins (3% of proteome), whereas PMA induced changed protein abundance of 207 (10 % of proteome) and LPS of 46 proteins (2% of proteome). Enrichment analyses clearly showed fundamental differences between stimuli, with primary association of IL8 stimulation to processes in immune response, receptor signaling and signal transduction. Top enrichment for PMA on the other hand pointed to vesicle mediated transport and exocytosis. Stimulation with LPS did not result in any significant enrichment. Although we detected 43% overlap of enrichment categories for IL8 and PMA stimulation, indicating that activation of neutrophils with different stimuli partly induces some similar biological processes and pathways, hierarchical clustering showed clear differences in distribution and biological relevance of clusters between the chosen stimuli. Our studies provide novel information on the granulocyte proteome and offer insights into early, differentiated granulocyte reaction to stimuli, which contribute to a better understanding of molecular mechanisms involved in activation and recruitment of neutrophils, through inflammatory stimuli.

Neutrophils extracellular traps damage Naegleria fowleri trophozoites opsonized with human IgG

Naegleria fowleri infects humans through the nasal mucosa causing a disease in the central nervous system known as primary amoebic meningoencephalitis (PAM). Polymorphonuclear cells (PMNs) play a critical role in the early phase of N. fowleri infection. Recently, a new biological defence mechanism called neutrophil extracellular traps (NETs) has been attracting attention. NETs are composed of nuclear DNA combined with histones and antibacterial proteins, and these structures are released from the cell to direct its antimicrobial attack. In this work, we evaluate the capacity of N. fowleri to induce the liberation of NETs by human PMN cells. Neutrophils were cocultured with unopsonized or IgG-opsonized N. fowleri trophozoites. DNA, histone, myeloperoxidase (MPO) and neutrophil elastase (NE) were stained, and the formation of NETs was evaluated by confocal microscopy and by quantifying the levels of extracellular DNA. Our results showed N. fowleri induce the liberation of NETs including release of MPO and NE by human PMN cells as exposure interaction time is increased, but N. fowleri trophozoites evaded killing. However, when trophozoites were opsonized, they were susceptible to the neutrophils activity. Therefore, our study suggests that antibody-mediated PMNs activation through NET formation may be crucial for antimicrobial responses against N. fowleri.

Effect of beta-adrenergic agents on human neutrophil granulocyte activation with N-formyl-methionyl-leucyl-phenylalanine and phorbol myristate acetate

Generation of reactive oxygen intermediates by activated polymorphonuclear neutrophil granulocytes plays an important role in development of microcirculatory injury. The effect of the beta 2-adrenergic receptor agonists (beta 2-agonists) isoprenaline and terbutaline on the chemiluminescence or oxygen consumption of human granulocytes in response to activation with n-formyl-methionyl-leucyl-phenylalanine (FMLP) and phorbol myristate acetate (PMA) was examined. The beta 2-agonist effect on activated cell aggregation and volume change was examined as well. As E. Coli lipopolysaccharide and FMLP may prime granulocytes for enhanced generation of reactive oxygen intermediates in response to other activators, the effect of beta 2-agonists on the priming effect of these agents was also investigated.

RESULTS

1) Optimal concentrations of beta 2-agonists decrease the human granulocyte generation of reactive oxygen intermediates in response to activation with FMLP by 40-60%, without affecting the response to PMA. 2) beta 2-Agonists modify the priming effect of FMLP on activation with PMA, but do not interfere with the priming effect of E. Coli lipopolysaccharide on activation with FMLP. 3) Isoprenaline have different effects on generation of reactive oxygen intermediates and cell aggregation in FMLP-activated granulocytes. 4) High concentrations of isoprenaline and terbutaline have contrasting non-specific effects on the chemiluminescence, but not on the oxygen consumption, of activated granulocytes.