Bactericidal Capacity Of Macrophages Research Articles

Raman Spectroscopy Profiling of Splenic T-Cells in Sepsis and Endotoxemia in Mice.

Sepsis is a life-threatening condition that results from an overwhelming and disproportionate host response to an infection. Currently, the quality and extent of the immune response are evaluated based on clinical symptoms and the concentration of inflammatory biomarkers released or expressed by the immune cells. However, the host response toward sepsis is heterogeneous, and the roles of the individual immune cell types have not been fully conceptualized. During sepsis, the spleen plays a vital role in pathogen clearance, such as bacteria by an antibody response, macrophage bactericidal capacity, and bacterial endotoxin detoxification. This study uses Raman spectroscopy to understand the splenic T-lymphocyte compartment profile changes during bona fide bacterial sepsis versus hyperinflammatory endotoxemia. The Raman spectral analysis showed marked changes in splenocytes of mice subjected to septic peritonitis principally in the DNA region, with minor changes in the amino acids and lipoprotein areas, indicating significant transcriptomic activity during sepsis. Furthermore, splenocytes from mice exposed to endotoxic shock by injection of a high dose of lipopolysaccharide showed significant changes in the protein and lipid profiles, albeit with interindividual variations in inflammation severity. In summary, this study provided experimental evidence for the applicability and informative value of Raman spectroscopy for profiling the immune response in a complex, systemic infection scenario. Importantly, changes within the acute phase of inflammation onset (24 h) were reliably detected, lending support to the concept of early treatment and severity control by extracorporeal Raman profiling of immunocyte signatures.

MILD TRAUMATIC BRAIN INJURY ATTENUATES PNEUMONIA-INDUCED LUNG INJURY BY MODULATIONS OF ALVEOLAR MACROPHAGE BACTERICIDAL ACTIVITY AND M1 POLARIZATION.

Traumatic brain injury is one of the main causes of death and disability worldwide, and results in multisystem complications. However, the mechanism of mild traumatic brain injury (MTBI) on lung injury remains unclear. In this study, we used a murine model of MTBI and pneumonia ( Pseudomonas aeruginosa ;) to explore the relationship between these conditions and the underlying mechanism. Methods: Mice (n = 104) were divided into control, MTBI, pneumonia, and MTBI + pneumonia groups. MTBI was induced by the weight-drop method. Pneumonia was induced by intratracheal injection with P. aeruginosa Xen5 strain. Animals were killed 24 h after bacterial challenging. Histological, cellular, and molecular indices of brain and lung injury were assessed using various methods. Results: Mice in both the MTBI and pneumonia groups had more Fluoro-Jade C-positive neurons than did the controls ( P < 0.01), but mice in the MTBI + pneumonia group had fewer Fluoro-Jade C-positive cells than did the pneumonia group ( P < 0.01). The MTBI + pneumonia mice showed decreased bacterial load ( P < 0.05), reduced lung injury score and pulmonary permeability ( P < 0.01), less inflammatory cells, and lower levels of proinflammatory cytokines (TNF-α and IL-1β; P < 0.01) when compared with the pneumonia group. Molecular analysis indicated lower levels of phosphorylated nuclear factor-κB in the lung of MTBI + pneumonia mice compared with the pneumonia group ( P < 0.01). Furthermore, alveolar macrophages from MTBI mice exhibited enhanced bactericidal capacity compared with those from controls ( P < 0.01). Moreover, MTBI + pneumonia mice exhibited less CD86-positive M1 macrophages compared with the pneumonia group ( P < 0.01). Conclusions: MTBI attenuates pneumonia-induced acute lung injury through the modulation of alveolar macrophage bactericidal capacity and M1 polarization in bacterial pneumonia model.

Immunomodulatory activity and protective effects of chokeberry fruit extract on Listeria monocytogenes infection in mice.

Chokeberry (Aronia melanocarpa) fruit extracts (CE) are rich in polyphenols and usually exhibit immunomodulatory, anti-viral and anti-bacterial effects. We have previously shown that the CE used in this study activated macrophages and stimulated effector T cell differentiation in vitro. When applied orally to healthy mice, CE increased the proportion of CD11c+ dendritic cells in the gut-associated lymphoid tissue. CE-pretreated BALB/c mice readily eradicated orally ingested Listeria monocytogenes as evidenced by a slighter decrease in body weight and number of bacteria recovered from the spleen and reduced spleen size compared to the control infected mice. CE pretreatment in infected mice resulted in higher proportions of CD11b+ macrophages and CD8+ cytotoxic T cells both in the gut and the spleen. Phagocytosis, reactive oxygen species production and the proportions of activated CD86+ macrophages (CD11b+) and dendritic cells (CD11c+) were also enhanced in CE-pretreated infected mice. Furthermore, the expression of inducible nitric oxide synthase and IL-6 was increased in CE-pretreated infected mice and similar results were obtained in peritoneal macrophages in vitro. This effect of CE was associated with increased phosphorylation of IκB and Notch1 production. Finally, CE pretreatment elevated the proportion of perforin-producing cells in the spleen compared to control infected mice. This study demonstrates that prophylactic treatment with CE leads to more rapid eradication of bacterial infection with L. monocytogenes predominantly through increased activity of myeloid cells in the gut and in the spleen.

The Endoplasmic Reticulum Stress Sensor Inositol-Requiring Enzyme 1α Augments Bacterial Killing through Sustained Oxidant Production.

ABSTRACTBacterial infection can trigger cellular stress programs, such as the unfolded protein response (UPR), which occurs when misfolded proteins accumulate within the endoplasmic reticulum (ER). Here, we used the human pathogen methicillin-resistant Staphylococcus aureus (MRSA) as an infection model to probe how ER stress promotes antimicrobial function. MRSA infection activated the most highly conserved unfolded protein response sensor, inositol-requiring enzyme 1α (IRE1α), which was necessary for robust bacterial killing in vitro and in vivo. The macrophage IRE1-dependent bactericidal activity required reactive oxygen species (ROS). Viable MRSA cells excluded ROS from the nascent phagosome and strongly triggered IRE1 activation, leading to sustained generation of ROS that were largely Nox2 independent. In contrast, dead MRSA showed early colocalization with ROS but was a poor activator of IRE1 and did not trigger sustained ROS generation. The global ROS stimulated by IRE1 signaling was necessary, but not sufficient, for MRSA killing, which also required the ER resident SNARE Sec22B for accumulation of ROS in the phagosomal compartment. Taken together, these results suggest that IRE1-mediated persistent ROS generation might act as a fail-safe mechanism to kill bacterial pathogens that evade the initial macrophage oxidative burst.

Crosstalk between circadian rhythmicity, mitochondrial dynamics and macrophage bactericidal activity

Biological functions show rhythmic fluctuations with 24-hr periodicity regulated by circadian proteins encoded by the so-called 'clock' genes. The absence or deregulation of circadian proteins in mice leads to metabolic disorders and in vitro models have shown that the synthesis of pro-inflammatory cytokines by macrophages follows a circadian rhythm so showing a link between circadian rhythmicity, metabolism and immunity. Recent evidence reveals that mitochondrial shape, position and size, collectively referred to as mitochondrial dynamics, are related to both cell metabolism and immune function. However, studies addressing the simultaneous crosstalk between circadian rhythm, mitochondrial dynamics and cell immune function are scarce. Here, by using an in vitro model of synchronized murine peritoneal macrophages, we present evidence that the mitochondrial dynamics and the mitochondrial membrane potential (∆ψm ) follow a circadian rhythmic pattern. In addition, it is shown that the fusion of mitochondria along with high ∆ψm , indicative of high mitochondrial activity, precede the highest phagocytic and bactericidal activity of macrophages on Salmonella typhimurium. Taken together, our results suggest a timely coordination between circadian rhythmicity, mitochondrial dynamics, and the bactericidal capacity of macrophages.

SPLENECTOMY AND SEPSIS: THE ROLE OF THE SPLEEN IN THE IMMUNE-MEDIATED BACTERIAL CLEARANCE

Over the past few years, many observations of overwhelming post splenectomy bacterial infections have been reported. Streptococcus pneumoniae is the aetiologic agent in about 80% of cases, but also gram-negative bacteria are involved in the development of fatal infections in splenectomized patients. Functionally, the spleen plays a fundamental role in bacterial clearance either by antibody response or macrophage bactericidal capacity. At the same time, there is evidence that the spleen also contributes to bacterial endotoxin detoxification. Finally, the mechanisms responsible for gram-positive and gram-negative sepsis in the splenectomized host and possible therapeutical approaches able to neutralize bacterial products endowed with noxious effects are discussed.

Phagocytic and bactericidal function of mouse macrophages to Salmonella typhimurium in schistosomiasis mansoni.

Patients infected with schistosomes may develop a clinical picture of chronic salmonellosis. We have investigated the altered function of macrophages capable of playing a role in the development of chronic salmonellosis associated with Schistosoma mansoni in an experimental model. The capacity of mouse peritoneal macrophages to ingest and kill Salmonella was assessed in mice infected with S. mansoni with or without concurrent Salmonella typhimurium infection. Schistosomiasis was associated with a significant decrease in the phagocytic index of macrophages, due to the reduced number of cells engaged in phagocytosis. However, the number of bacteria ingested by these cells was comparable to that of the control group. The bactericidal capacity of macrophages from S. mansoni-infected mice was also significantly lower than that of cells from normal mice. Macrophages from animals infected only with Salmonella typhimurium showed an increased phagocytic capacity. It was concluded that S. mansoni infection alters phagocytosis and intracellular destruction of salmonellae. This demonstration of a novel mechanism of survival of salmonellae represents a step forward in understanding the pathogenesis and management of chronic septicemic salmonellosis.

In vivo analysis of impaired macrophage bactericidal capacity during experimental African trypanosomiasis.

Since innate resistance of mice to Salmonella typhimurium depends on an intact macrophage system, we have used this bacterium to investigate the effect of Trypanosoma brucei subsp. rhodesiense infection on macrophage phagocytic and cytolytic function. CBA/CaJ mice infected with T. brucei subsp. rhodesiense have decreased resistance to S. typhimurium, since doubly infected mice rapidly succumb to sublethal doses of S. typhimurium. Although trypanosomiasis is known to suppress antibody formation, such a suppression of antibody does not seem to play a role in trypanosome-induced sensitivity to S. typhimurium. A trypanosome-induced blockade of the reticuloendothelial system also does not occur, since parasitized and control mice clear S. typhimurium from the blood equally well. Early killing (0 to 48 h) of S. typhimurium in the liver and spleen is mainly macrophage mediated, and mice infected with trypanosomes kill S. typhimurium in the liver and spleen very poorly. Apparently trypanosomiasis inhibits macrophage bactericidal activity, but has no effect on phagocytosis.

Host defenses in murine malaria: analysis of plasmodial infection-caused defects in macrophage microbicidal capacities.

Macrophage-dependent killing of facultative intracellular bacteria was markedly impaired by overt erythrocytic Plasmodium yoelii or Plasmodium berghei infection of mice. P. yoelii infection was capable of ablating not only the macrophage microbicidal capacity of "normal" animals but also the bactericidal capacities of "activated" macrophages. The uptake by spleen and liver of an intravenous challenge of Listeria monocytogenes was not altered by plasmodial infection, but within hours of injection markedly enhanced bacterial growth was found in tissues of malarious mice. The evidence gives credence to the view that the uptake of bacteria by macrophages of malarious mice was normal but that malarious mice, unlike normal mice, were unable to kill the bacteria. The plasmodial infection-caused defect in macrophage microbicidal capacity could be partially mimicked by the intravenous injection of large numbers of nonreplicating heterologous particles (i.e., killed bacteria, sheep erythrocytes). This result suggests that the uptake of particles generated during overt erythrocytic malaria may be responsible for the malaria-associated defects in macrophage bactericidal capacity.

Enhancement of macrophage bactericidal capacity by antigenically stimulated immune lymphocytes

The ability of antigenically stimulated immune lymphocytes to influence the bactericidal capacity of normal macrophages was studied in vitro. Purified lymphocytes were obtained from the lymph nodes and peritoneal exudates of guinea pigs immunized with bovine gamma globulin (BGG) and from control animals. Immune and control lymphocytes were added to normal macrophages and incubated overnight in the presence or absence of BGG. After washing, the macrophage monolayers were infected with Listeria monocytogenes; 4 hr later, the cells were lysed and the surviving intracellular bacteria quantitated. The macrophages which had been incubated with BGG-immune lymphocytes in the presence of BGG displayed a markedly enhanced listericidal capacity. In parallel experiments, these same antigen-stimulated lymphocytes were shown to inhibit the migration of normal macrophages. Lymphocytes derived from peritoneal exudates were more active than lymph node lymphocytes in both assays.

Cellular immunity in vitro. I. Immunologically mediated enhancement of macrophage bactericidal capacity.

An in vitro model of cellular immunity in the guinea pig was established. Animals were immunized with tubercle bacilli, bovine gamma globulin, or picrylated human serum albumin in complete Freund's adjuvant. Oil-induced peritoneal exudates from immune and control animals were cultured overnight with and without specific antigen. The cultures were washed and the macrophage monolayers were infected with Listeria monocytogenes. At intervals the monolayers were lysed and the numbers of viable intracellular bacteria were quantitated by pour plate cultures. Random monolayers were also evaluated in sequence by visually counting the intracellular bacteria on Gram-stained plates. Both methods demonstrated that the macrophages from immune animals had markedly enhanced listericidal activity when the peritoneal exudates were cultured with antigen before infection. Macrophage migration inhibition was also demonstrated under these conditions. The experiments reported here describe an in vitro model of cellular immunity which will allow separation and recombination of cell types and direct assay of cell products in efforts to elucidate further the mechanisms of the immunologically mediated enhancement of macrophage bactericidal capacity.