Phagocytosis of live and dead Escherichia coli and Staphylococcus aureus in human whole blood is markedly reduced by combined inhibition of C5aR1 and CD14

Intravital Microscopy for Imaging and Live Cell Tracking of Alveolar Macrophages in Real Time

Classic in vitro coculture assays of pathogens with host cells have contributed significantly to our understanding of the intracellular lifestyle of several pathogens. Coculture assays with pathogens and eukaryotic cells can be analyzed through various techniques including plating for colony-forming units (CFU), confocal microscopy, and flow cytometry. However, findings from in vitro assays require validation in an in vivo model. Several physiological conditions can influence host-pathogen interactions, which cannot easily be mimicked in vitro. Intravital microscopy (IVM) is emerging as a powerful tool for studying host-pathogen interactions by enabling in vivo imaging of living organisms. As a result, IVM has significantly enhanced the understanding of infection mediated by diverse pathogens. The versatility of IVM has also allowed for the imaging of various organs as sites of local infection. This chapter specifically focuses on IVM conducted on the lung for elucidating pulmonary immune response, primarily involving alveolar macrophages, to pathogens. Additionally, in this chapter we outline the protocol for lung IVM that utilizes a thoracic suction window to stabilize the lung for acquiring stable images.

Anaphylatoxin signaling activates macrophages to control intracellular Rickettsia proliferation

IMPORTANCE

Pathogenic Rickettsia species are extremely dangerous bacteria that grow within the cytoplasm of host mammalian cells. In most cases, these bacteria are able to overpower the host cell and grow within the protected environment of the cytoplasm. However, a dramatic conflict occurs when Rickettsia encounter innate immune cells; the bacteria can "win" by taking over the host, or the bacteria can "lose" if the host cell efficiently fights the infection. This manuscript examines how the immune complement system is able to detect the presence of Rickettsia and alert nearby cells. Byproducts of complement activation called anaphylatoxins are signals that "activate" innate immune cells to mount an aggressive defensive strategy. This study enhances our collective understanding of the innate immune reaction to intracellular bacteria and will contribute to future efforts at controlling these dangerous infections.

Thrombin Differentially Modulates the Acute Inflammatory Response to Escherichia coli and Staphylococcus aureus in Human Whole Blood

Thrombin plays a central role in thromboinflammatory responses, but its activity is blocked in the common ex vivo human whole blood models, making an ex vivo study of thrombin effects on thromboinflammatory responses unfeasible. In this study, we exploited the anticoagulant peptide Gly-Pro-Arg-Pro (GPRP) that blocks fibrin polymerization to study the effects of thrombin on acute inflammation in response to Escherichia coli and Staphylococcus aureus Human blood was anticoagulated with either GPRP or the thrombin inhibitor lepirudin and incubated with either E. coli or S. aureus for up to 4 h at 37°C. In GPRP-anticoagulated blood, there were spontaneous elevations in thrombin levels and platelet activation, which further increased in the presence of bacteria. Complement activation and the expression of activation markers on monocytes and granulocytes increased to the same extent in both blood models in response to bacteria. Most cytokines were not elevated in response to thrombin alone, but thrombin presence substantially and heterogeneously modulated several cytokines that increased in response to bacterial incubations. Bacterial-induced releases of IL-8, MIP-1α, and MIP-1β were potentiated in the thrombin-active GPRP model, whereas the levels of IP-10, TNF, IL-6, and IL-1β were elevated in the thrombin-inactive lepirudin model. Complement C5-blockade, combined with CD14 inhibition, reduced the overall cytokine release significantly, both in thrombin-active and thrombin-inactive models. Our data support that thrombin itself marginally induces leukocyte-dependent cytokine release in this isolated human whole blood but is a significant modulator of bacteria-induced inflammation by a differential effect on cytokine patterns.

Folic acid-mediated fibrosis is driven by C5a receptor 1-mediated activation of kidney myeloid cells

We have previously reported that increased expression and activation of kidney cell complement components play an important role in the pathogenesis of renal scarring. Here, we used floxed green fluorescent protein (GFP)-C5a receptor 1 (C5aR1) knockin mice (GFP-C5ar1fl/fl) and the model of folic acid (FA)-induced kidney injury to define the cell types and potential mechanisms by which increased C5aR1 activation leads to fibrosis. Using flow cytometry and confocal microscopy, we identified macrophages as the major interstitial cell type showing increased expression of C5aR1 in FA-treated mice. C5ar1fl/fl.Lyz2Cre+/- mice, in which C5aR1 has been specifically deleted in lysozyme M-expressing myeloid cells, experienced reduced fibrosis compared with control C5ar1fl/fl mice. Examination of C5aR1-expressing macrophage transcriptomes by gene set enrichment analysis demonstrated that these cells were enriched in pathways corresponding to the complement cascade, collagen formation, and the NABA matrisome, strongly pointing to their critical roles in tissue repair/scarring. Since C5aR1 was also detected in a small population of platelet-derived growth factor receptor-β+ GFP+ cells, we developed C5ar1fl/fl.Foxd1Cre+/- mice, in which C5aR1 is deleted specifically in pericytes, and found reduced FA-induced fibrosis. Primary cell cultures of platelet-derived growth factor receptor-β+ pericytes isolated from FA-treated C5ar1fl/fl.Foxd1Cre+/- mice showed reduced secretion of several cytokines, including IL-6 and macrophage inflammatory protein-2, compared with pericytes isolated from FA-treated control GFP-C5ar1fl/fl mice. Collectively, these data imply that C5a/C5aR1 axis activation primarily in interstitial cells contributes to the development of renal fibrosis.NEW & NOTEWORTHY This study used novel green fluorescent protein C5a receptor 1 floxed mice and the model of folic acid-mediated kidney fibrosis to demonstrate the pathogenic role of increased expression of this complement receptor on macrophages.

Vitamin C, Hydrocortisone, and the Combination Thereof Significantly Inhibited Two of Nine Inflammatory Markers Induced by Escherichia Coli But Not by Staphylococcus Aureus - When Incubated in Human Whole Blood

ABSTRACT

Vitamin C combined with hydrocortisone is increasingly being used to treat septic patients, even though this treatment regimen is based on questionable evidence. When used, a marked effect on key players of innate immunity would be expected, as sepsis is featured by a dysregulated immune response.Here, we explored the effect of vitamin C and hydrocortisone alone and combined, in an ex vivo human whole-blood model of Escherichia coli- or Staphylococcus aureus-induced inflammation. Inflammatory markers for activation of complement (terminal C5b-9 complement complex [TCC]), granulocytes (myeloperoxidase), platelets (β-thromboglobulin), cytokines (tumor necrosis factor [TNF], IL-1β, IL6, and IL-8), and leukocytes (CD11b and oxidative burst) were quantified, by enzyme-linked immunosorbent assay, multiplex technology, and flow cytometry.In E. coli- and S. aureus-stimulated whole blood, a broad dose-titration of vitamin C and hydrocortisone alone did not lead to dose-response effects for the central innate immune mediators TCC and IL-6. Hence, the clinically relevant doses were used further. Compared to the untreated control sample, two of the nine biomarkers induced by E. coli were reduced by hydrocortisone and/or vitamin C. TNF was reduced by hydrocortisone alone (19%, P = 0.01) and by the combination (31%, P = 0.01). The oxidative burst of monocytes and granulocytes was reduced for both drugs alone and their combination, (ranging 8-19%, P < 0.05). Using S. aureus, neither of the drugs, alone nor in combination, had any effects on the nine biomarkers.In conclusion, despite the limitation of the ex vivo model, the effect of vitamin C and hydrocortisone on bacteria-induced inflammatory response in human whole blood is limited and following the clinical data.

CD14 inhibition improves survival and attenuates thrombo-inflammation and cardiopulmonary dysfunction in a baboon model of Escherichia coli sepsis

BACKGROUND

During sepsis, gram-negative bacteria induce robust inflammation primarily via lipopolysacharride (LPS) signaling through TLR4, a process that involves the glycosylphosphatidylinositol (GPI)-anchored receptor CD14 transferring LPS to the Toll-like receptor 4/myeloid differentiation factor 2 (TLR4/MD-2) complex. Sepsis also triggers the onset of disseminated intravascular coagulation and consumptive coagulopathy.

OBJECTIVES

We investigated the effect of CD14 blockade on sepsis-induced coagulopathy, inflammation, organ dysfunction, and mortality.

METHODS

We used a baboon model of lethal Escherichia (E) coli sepsis to study two experimental groups (n = 5): (a) E coli challenge; (b) E coli challenge plus anti-CD14 (23G4) inhibitory antibody administered as an intravenous bolus 30 minutes before the E coli.

RESULTS

Following anti-CD14 treatment, two animals reached the 7-day end-point survivor criteria, while three animals had a significantly prolonged survival as compared to the non-treated animals that developed multiple organ failure and died within 30 hours. Anti-CD14 reduced the activation of coagulation through inhibition of tissue factor-dependent pathway, especially in the survivors, and enhanced the fibrinolysis due to strong inhibition of plasminogen activator inhibitor 1. The treatment prevented the robust complement activation induced by E coli, as shown by significantly decreased C3b, C5a, and sC5b-9. Vital signs, organ function biomarkers, bacteria clearance, and leukocyte and fibrinogen consumption were all improved at varying levels. Anti-CD14 reduced neutrophil activation, cell death, LPS levels, and pro-inflammatory cytokines (tumor necrosis factor, interleukin (IL)-6, IL-1β, IL-8, interferon gamma, monocyte chemoattractant protein-1), more significantly in the survivors than non-surviving animals.

CONCLUSIONS

Our results highlight the crosstalk between coagulation/fibrinolysis, inflammation, and complement systems and suggest a protective role of anti-CD14 treatment in E coli sepsis.

TLR8 and complement C5 induce cytokine release and thrombin activation in human whole blood challenged with Gram-positive bacteria

We recently showed that TLR8 is critical for the detection of Gram-positive bacteria by human monocytes. Here, we hypothesized that TLR8 and complement together regulate antibacterial responses in human blood. Anticoagulated blood was treated with selective inhibitors of TLR8 and/or complement C5, and then challenged with live Streptococcus agalactiae (Group B streptococcus, GBS), Staphylococcus aureus, or Escherichia coli. Cytokine production, plasma membrane permeability, bacterial survival, phagocytosis, and activation of coagulation was examined. GBS and S. aureus, but not E. coli, triggered TLR8-dependent production of IL-12p70, IL-1β, TNF, and IL-6 in fresh human whole blood. In purified polymorphonuclear neutrophils (PMN), GBS and S. aureus induced IL-8 release in part via TLR8, whereas PMN plasma membrane leakage and extracellular DNA levels increased independently of TLR8. TLR8 was more important than C5 for bacteria-induced production of IL-12p70, IL-1β, and TNF in blood, whereas IL-8 release was more C5 dependent. Both TLR8 and C5 induced IL-6 release and activation of prothrombin cleavage, and here their combined effects were additive. Blocking of C5 or C5aR1 attenuated phagocytosis and increased the extracellular growth of GBS in blood, whereas TLR8 inhibition neither reduced phagocytosis nor intracellular killing of GBS and S. aureus. In conclusion, TLR8 is more important than C5 for production of IL-12p70, IL-1β, and TNF upon GBS and S. aureus infection in blood, whereas C5 is central for IL-8 release and phagocytosis. Both TLR8 and C5 mediate IL-6 release and activation of coagulation during challenge with Gram-positive bacteria in blood.

Phagocytosis assays with different pH-sensitive fluorescent particles and various readouts

Phagocytosis is a fundamental mechanism of innate immunity and its impairment is associated with severe chronic diseases, for example, chronic obstructive pulmonary disease. Investigating phagocytosis requires flexible tools and assay conditions, such as different fluorescent particle types, detection colors and readouts. We comprehensively evaluated and optimized phagocytosis assays using particles labeled with fluorescent pH-sensitive pHrodo^® dyes, facilitating the specific detection of phagocytosed particles. Beads, bacterial and yeast particles labeled with pHrodo red and green were tested for their uptake by THP-1 cells and primary human macrophages by flow cytometry and high-content imaging. Whereas the latter allowed kinetic phagocytosis measurement, the former demonstrated the feasibility of using cell sorting for periods of up to 6 h, enabling downstream applications such as pooled genetic screens.