Macrophage hydrogen peroxide production and phagocytic function are decreased following phagocytosis mediated by Fc receptors but not complement receptors

Effect of Bromelain-Based Enzymatic Debridement on Skin Cells

Several reports have concluded that enzymatic debridement based on Bromelain (NX) is selective and efficient. Although clinical trials showed that viable tissue is not damaged at the macroscopic level, the effect on the cellular level is largely unknown. The current study is meant to close this gap by evaluating whether NX has an effect on vital cells of the human dermis on a cellular level. In an experimental in vitro study design, the effect of NX on human keratinocytes, fibroblasts, and macrophages was analyzed. Enzymatic treatment was performed for 4 hours by using either cell culture medium or phosphate-buffered saline as diluting agent for NX. Cell viability and relative cell number in relation to untreated control cells were determined using a resazurin-based assay. In addition, the development of enzyme activity during clinical treatment was analyzed: wound fluid collected from a burn wound at different points of debridement was applied on collagen-elastin disks to prove enzymatic digestion activity. Both keratinocytes and fibroblasts were damaged by NX even at low concentrations. Both cell types showed improved survival when a medium was used for dissolving NX. Macrophages appeared to resist NX treatment more efficiently than the other cell types. In the clinical trial, NX activity in the wound fluid decreased clearly following 4 hours of enzymatic debridement. NX induces toxicity of vital skin cells in vitro. However, macrophages appear to be more resistant against NX treatment in vitro. The inflammatory responses of vital cells in the burn wound itself are likely to inhibit NX activity. The effect of this inflammatory process on NX activity will have to be investigated in future studies.

Down-regulation of complement receptors on the surface of host monocyte even as in vitro complement pathway blocking interferes in dengue infection

In dengue virus (DENV) infection, complement system (CS) activation appears to have protective and pathogenic effects. In severe dengue fever (DF), the levels of DENV non-structural-1 protein and of the products of complement activation, including C3a, C5a and SC5b-9, are higher before vascular leakage occurs, supporting the hypothesis that complement activation contributes to unfavourable outcomes. The clinical manifestations of DF range from asymptomatic to severe and even fatal. Here, we aimed to characterise CS by their receptors or activation product, in vivo in DF patients and in vitro by DENV-2 stimulation on monocytes. In comparison with healthy controls, DF patients showed lower expression of CR3 (CD11b), CR4 (CD11c) and, CD59 on monocytes. The DF patients who were high producers of SC5b-9 were also those that showed more pronounced bleeding or vascular leakage. Those findings encouraged us to investigate the role of CS in vitro, using monocytes isolated from healthy subjects. Prior blocking with CR3 alone (CD11b) or CR3 (CD11b/CD18) reduced viral infection, as quantified by the levels of intracellular viral antigen expression and soluble DENV non-structural viral protein. However, we found that CR3 alone (CD11b) or CR3 (CD11b/CD18) blocking did not influence major histocompatibility complex presentation neither active caspase-1 on monocytes, thus probably ruling out inflammasome-related mechanisms. Although it did impair the secretion of tumour necrosis factor alpha and interferon alpha. Our data provide strategies of blocking CR3 (CD11b) pathways could have implications for the treatment of viral infection by antiviral-related mechanisms.

Changed phagocytic activity and pattern of Fcγ and complement receptors on blood monocytes in sarcoidosis

We have recently revealed that mycobacterial heat shock proteins (Mtb-hsp), involved in forming of immune complexes (CIs), can induce immune response in sarcoidosis (SA). The complexemia may result from inappropriate phagocytosis and clearance of CIs by monocytes with following persistent antigenemia and granuloma formation. Because an aberrant expression of receptors for Fc fragment of immunoglobulin G (FcγR) and complement receptors (CR) on monocytes can be involved in this process, we have evaluated the expression of FcγRI (CD64), FcγRII (CD32), FcγRIII (CD16) and CR1 (CD35), CR3 (CD11b), CR4 (CD11c) receptors on blood CD14(+) monocytes and its phagocytic activity in 24 patients with SA and 20 healthy volunteers using flow cytometry. We found significantly increased expression of all examined FcγR and decreased expression of CD35 and CD11c on CD14(+) monocytes in SA patients vs controls. Significantly increased percentage of CD14(+)CD16(+)CD35(-), CD14(+)CD64(+)CD35(+), CD14(+)CD64(+)CD11b(+), CD14(+)CD64(+)CD11c(+) and decreased of CD14(+)CD32(-)CD35(+), CD14(+)CD32(-)CD11b(+), CD14(+)CD32(-)CD11c(+) monocytes' phenotypes was revealed in SA. The total number and percentage of phagocyting monocytes was significantly increased in SA as compared with controls. In conclusion, altered expression of FcγR and CR on CD14(+) monocytes and its increased phagocytic activity may be responsible for high antigen load, persistent antigenemia and immunocomplexemia in SA patients.

Lysosomotropic agents ameliorate macrophage dysfunction following the phagocytosis of IgG-coated erythrocytes: a role for lipid peroxidation

Phagocytosis of IgG-coated erythrocytes (EIgG) can depress several macrophage functions. Our previous studies have suggested that this macrophage dysfunction may be due to an oxidative stress caused by the interaction of hemoglobin-derived iron with superoxide and/or hydrogen peroxide. Since lysosomotropic agents are capable of altering iron handling by macrophages, the present study evaluated the ability of these agents to prevent the macrophage dysfunction and lipid peroxidation caused by a phagocytic challenge with EIgG. Elicited rat peritoneal macrophages showed a depression of PMA-stimulated hydrogen peroxide production, calcium ionophore-stimulated arachidonate release and Fc receptor-mediated phagocytosis. The lysosomotropic agents; chloroquine, quinacrine, ammonium chloride and methylamine all prevented the depression of hydrogen peroxide production and arachidonate release but did not alter the depression of phagocytic function. These agents also prevented the increase in lipid peroxidation products caused by a phagocytic challenge with EIgG. These results suggest that the ability of lysosomotropic agents to prevent some aspects of macrophage dysfunction after a phagocytic challenge may be due to their ability to block the oxidative stress caused by the challenge.

Receptor-mediated phagocytosis of myelin by macrophages and microglia: effect of opsonization and receptor blocking agents

Myelin is phagocytosed by microglia (MG) and to a somewhat lesser extent by peritoneal macrophages (M phi) in a dose- and time-dependent manner. In serum-free medium opsonization of rat myelin significantly enhances binding and ingestion, more by rat macrophages than by microglia. Furthermore the requirement for opsonization is not restricted to anti-myelin antibodies as the difference in the rate of myelin uptake by macrophages is largely eliminated when they are cultured in 10% fetal calf serum. Binding and ingestion of both myelin and opsonized myelin are inhibited to the same dose-dependent extent by zymosan, oxidized LDL, peroxidase-antiperoxidase (PAP), opsonized erythrocytes and the anti-CR3 antibody OX42 implicating lectin, scavenger, Fc and complement receptors in the phagocytosis of myelin. Thus while the differential uptake of myelin and opsonized myelin by macrophages would indicate a central role for the Fc receptor, binding inhibition studies implicate a range of membrane receptors which would obviate the need for antigen-antibody complexing to stimulate phagocytosis. Uptake of both myelin preparations by macrophages or microglia is stimulated by interferon-gamma and inhibited by TGF-beta, and the process of ingestion results in increased nitric oxide release and decreased superoxide production, the effect being more pronounced when myelin is opsonized.

Simultaneous detection of free radical release and membrane current during phagocytosis

Stimulation of macrophages induces the "respiratory burst" response which is associated with the generation of superoxide (O2-), a drop in cytoplasmic pH, and a pronounced depolarization of the membrane potential. The purpose of the present studies was to determine whether an increase in O2- was temporally related to changes in membrane potential and transmembrane current. Release of O2- at the single cell level was photometrically monitored during phagocytosis of immune complexes while simultaneously measuring whole-cell current. Membrane depolarization and the generation of a non-selective current followed an increase in O2- production with a variable lag time which was correlated with the state of cellular maturation in culture. In the absence of phagocytosis, the exposure of macrophages to O2- generated by a xanthine-xanthine oxidase reaction activated a non-selective current similar to that seen after phagocytosis. These results provide the first demonstration of the relationship between free radical release and the ensuing electrophysiological signaling events which are linked to particle engulfment in phagocytic cells.

Partial characterization of a low molecular weight phagocytosis inhibitory factor obtained from human erythrocyte membranes

Phagocytosis Inhibitory Factor (PIF), a small (< 3000 D) molecule, was partially purified from human red blood cell membranes. This factor inhibits latex phagocytosis by monocytic cells. PIF is not toxic under the experimental conditions employed and the phagocytosis inhibitory activity is reversible since removal of this factor restores the phagocytic capability of cells. The phagocytic activity of murine macrophages was not affected by PIF.