Diversity of in vitro cytokine responses by human macrophages to infection by mycobacterium tuberculosis strains

Macrophages are an important component in the first line of defence of the innate immune system. They are capable of producing cytokines in response to bacterial challenge, as well as in response to cytokine stimuli from other cells in the immune system. The microbicidal response of human monocyte-derived macrophages in vitro, induced by exogenously added cytokines, is highly variable. We found that tumour necrosis factor-alpha (TNF-alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF) could have either stimulatory or inhibitory effects on intracellular BCG killing, depending on the macrophage donor. Macrophages infected in vitro by various clinical isolates of Mycobacterium tuberculosis or the laboratory strain H37Rv, produced varying levels of both TNF-alpha and IFN-gamma. Certain M. tuberculosis strains tended to be associated with high cytokine production in each of three independent experiments, indicating that strains may differ in the host response elicited to infection.     

Murine cytomegalovirus infection inhibits tumor necrosis factor alpha responses in primary macrophages

Despite robust host immune responses the betaherpesvirus murine cytomegalovirus (MCMV) is able to establish lifelong infection. This capacity is due at least in part to the virus utilizing multiple immune evasion mechanisms to blunt host responses. Macrophages are an important cell for MCMV infection, dissemination, and latency despite expression in the host of multiple cytokines, including tumor necrosis factor alpha (TNF-alpha), that can induce an antiviral state in macrophages or other cells. In this study, we found that MCMV infection of bone marrow-derived macrophages inhibited TNF-alpha-induced ICAM-1 surface expression and mRNA expression in infected cells via expression of immediate early and/or early viral genes. MCMV infection blocked TNF-alpha-induced nuclear translocation of NF-kappaB. This inhibition of TNF-alpha signaling was explained by a decrease in TNF receptor 1 (TNFR1) and TNFR2 that was due to decreased mRNA for the latter. These findings provide a mechanism by which MCMV can evade the effects of an important host cytokine in macrophages.     

Origin,production and molecular determinants of macrophages for their therapeutic targeting

Macrophages, the most heterogeneous cells of the hematopoietic system and the giant eaters of the immune system that present either as tissue-resident cells or infiltrated immune cells, eliminate foreign pathogens and microbes and also play different physiological roles to maintain the body's immune response. In this review, we basically provide a broad overview of macrophages from their origin, functional diversity to M1-M2 polarization, specialized markers, and their role as important therapeutic targets in different diseases based on the current research and evidence. Apart from this, we have precisely discussed about tumor-associated macrophages (TAMs) and their role in tumor progression and newly discovered lesser-known markers of TAMs that could be used as potential therapeutic targets to treat life-threatening diseases. It is really very important to understand the diversity of macrophages to develop TAM-modulating strategies to activate our own immune system against diseases and to overcome immune resistance.     

Isolation,characterisation and phagocytic function of human macrophages from human peripheral blood

Molecular Biology Reports - Macrophages are among the most important cells of the immune system. Among other functions, they take part in almost all defense actions against foreign bodies and...     

Living in the danger zone: innate immunity to Salmonella

Phagocytic cells, including macrophages, neutrophils and dendritic cells, are critical components of the innate immune response to bacterial pathogens such as Salmonella typhimurium. These cells can have several roles during the early stage of an infection including controlling bacterial replication and producing cytokines and chemokines that activate and recruit additional cells. Macrophages, neutrophils and dendritic cells increase in number early after oral Salmonella infection and produce cytokines important in host survival such as tumor necrosis factor alpha (TNF-alpha). All three phagocytic cell types also harbor bacteria during infection. Natural killer cells, natural killer T cells and T cell receptor alpha beta T cells also respond rapidly to infection and are early sources of interferon-gamma during infection with Salmonella. Studies using infection models with Salmonella are providing a picture of the innate response to bacteria and insight into the role of defined cell types and cytokines important in the transition from innate to adaptive immunity.     

Activation of P2X(7) receptor by ATP plays an important role in regulating inflammatory responses during acute viral infection

Acute viral infection causes damages to the host due to uncontrolled viral replication but even replication deficient viral vectors can induce systemic inflammatory responses. Indeed, overactive host innate immune responses to viral vectors have led to devastating consequences. Macrophages are important innate immune cells that recognize viruses and induce inflammatory responses at the early stage of infection. However, tissue resident macrophages are not easily activated by the mere presence of virus suggesting that their activation requires additional signals from other cells in the tissue in order to trigger inflammatory responses. Previously, we have shown that the cross-talk between epithelial cells and macrophages generates synergistic inflammatory responses during adenoviral vector infection. Here, we investigated whether ATP is involved in the activation of macrophages to induce inflammatory responses during an acute adenoviral infection. Using a macrophage-epithelial cell co-culture system we demonstrated that ATP signaling through P2X(7) receptor (P2X(7)R) is required for induction of inflammatory mediators. We also showed that ATP-P2X(7)R signaling regulates inflammasome activation as inhibition or deficiency of P2X(7)R as well as caspase-1 significantly reduced IL-1β secretion. Furthermore, we found that intranasal administration of replication deficient adenoviral vectors in mice caused a high mortality in wild-type mice with symptoms of acute respiratory distress syndrome but the mice deficient in P2X(7)R or caspase-1 showed increased survival. In addition, wild-type mice treated with apyrase or inhibitors of P2X(7)R or caspase-1 showed higher rates of survival. The improved survival in the P2X(7)R deficient mice correlated with diminished levels of IL-1β and IL-6 and reduced neutrophil infiltration in the early phase of infection. These results indicate that ATP, released during viral infection, is an important inflammatory regulator that activates the inflammasome pathway and regulates inflammatory responses.     

Are Macrophages in Tumors Good Targets for Novel Therapeutic Approaches?

The development of cancer has been an extensively researched topic over the past few decades. Although great strides have been made in cancer prevention, diagnosis, and treatment, there is still much to be learned about cancer’s micro-environmental mechanisms that contribute to cancer formation and aggressiveness. Macrophages, lymphocytes which originate from monocytes, are involved in the inflammatory response and often dispersed to areas of infection to fight harmful antigens and mutated cells in tissues. Macrophages have a plethora of roles including tissue development and repair, immune system functions, and inflammation. We discuss various pathways by which macrophages get activated, various approaches that can regulate the function of macrophages, and how these approaches can be helpful in developing new cancer therapies.     

An unexpected role for hypoxic response: oxygenation and inflammation

The eradication of invading microorganisms depends initially on innate immunity mechanisms that preexist in all individuals and act within minutes of infection. Pathogen spread is often countered by an inflammatory response that recruits more effector molecules and cells of the innate immune system from local blood vessels, while inducing clotting farther downstream so that pathogens cannot spread throughout the blood. If a microorganism crosses an epithelial barrier and begins to replicate in the tissues of the host, it is, in some cases, immediately recognized by the mononuclear phagocytes, or macrophages, that reside in tissues. Macrophages mature continuously from circulating monocytes that leave the circulation to migrate into tissues throughout the body. The second major family of phagocytes, the neutrophils or polymorphonuclear leukocytes (PMNs) are short-lived cells that are abundant cells in the blood but are not present in healthy tissues. Both phagocytic cell types play a key role in innate immunity because they can recognize, ingest and destroy many pathogens without the aid of an adaptive immune response. This infiltration of neutrophils and later macrophages to the site of bacterial infection is tightly linked with the need of these immune defense cells to respond to the tissue microenvironment.     

Phagocyte sabotage: disruption of macrophage signalling by bacterial pathogens

Macrophages function at the front line of immune defences against incoming pathogens. But the ability of macrophages to internalize bacteria, migrate, recruit other immune cells to the site of infection and influence the nature of the immune response can provide unintended benefits for bacterial pathogens that are able to subvert or co-opt these normally effective defences. This review highlights recent advances in our understanding of the many interference strategies that are used by bacterial pathogens to undermine macrophage signalling.     

An Unexpected Role for Hypoxic Response: Oxygenation and Inflammation

The eradication of invading microorganisms depends initially on innate immunity mechanisms that preexist in all individuals and act within minutes of infection. Pathogen spread is often countered by an inflammatory response that recruits more effector molecules and cells of the innate immune system from local blood vessels, while inducing clotting farther downstream so that pathogens cannot spread throughout the blood. If a microorganism crosses an epithelial barrier and begins to replicate in the tissues of the host, it is, in some cases, immediately recognized by the mononuclear phagocytes, or macrophages, that reside in tissues. Macrophages mature continuously from circulating monocytes that leave the circulation to migrate into tissues throughout the body. The second major family of phagocytes, the neutrophils or polymorphonuclear leukocytes (PMNs) are short-lived cells that are abundant cells in the blood but are not present in healthy tissues. Both phagocytic cell types play a key role in innate immunity because they can recognize, ingest and destroy many pathogens without the aid of an adaptive immune response. This infiltration of neutrophils and later macrophages to the site of bacterial infection is tightly linked with the need of these immune defense cells to respond to the tissue microenvironment.     

An SopB-mediated immune escape mechanism of Salmonella enterica can be subverted to optimize the performance of live attenuated vaccine carrier strains

Salmonellae have evolved several mechanisms to evade host clearance. Here, we describe the influence on bacterial immune escape of the effector protein SopB, which is translocated into the cytosol through a type III secretion system. Wild-type bacteria, as well as the sseC and aroA attenuated mutants exerted a stronger cytotoxic effect on dendritic cells (DC) than their SopB-deficient derivatives. Cells infected with the double sseC sopB, phoP sopB and aroA sopB mutants also exhibited higher expression of MHC, CD80, CD86 and CD54 molecules, and showed a stronger capacity to process and present an I-E(d)-restricted epitope from the influenza hemagglutinin (HA) to CD4+ cells from TCR-HA transgenic mice in vitro. The incorporation of an additional mutation into the sopB locus of the attenuated sseC, phoP and aroA mutants resulted in the stimulation of improved humoral and cellular immune responses following oral vaccination. The obtained results define a new potential immune escape strategy of this important pathogen, and also demonstrate that this mechanism can be subverted to optimize the immune responses elicited using Salmonella as a live vaccine carrier.     

Tuberculosis: Smart manipulation of a lethal host

Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a global threat to human health. Development of drug resistance and co‐infection with HIV has increased the morbidity and mortality caused by TB. Macrophages serve as primary defense against microbial infections, including TB. Upon recognition and uptake of mycobacteria, macrophages initiate a series of events designed to lead to generation of effective immune responses and clearance of infection. However, pathogenic mycobacteria utilize multiple mechanisms for manipulating macrophage responses to protect itself from being killed and to survive within these cells that are designed to kill them. The outcomes of mycobacterial infection are determined by several host‐ and pathogen‐related factors. Significant advancements in understanding mycobacterial pathogenesis have been made in recent years. In this review, some of the important factors/mechanisms regulating mycobacterial survival inside macrophages are discussed.

     

Human monocyte activation for cytotoxicity against intracellular Leishmania donovani amastigotes: induction of microbicidal activity by interferon-gamma

Macrophages are pivotal cells in interactions of man and leishmania. Leishmanial disease results from intracellular infection of macrophages: parasitized cells are seen in smears or biopsy specimens of lesions; macrophages cultured in vitro support replication of parasites. Paradoxically, parasite destruction is also mediated by macrophages, which become highly cytotoxic after exposure to immune lymphocytes or their lymphokine (LK) products. The precise molecular mechanisms by which lymphocytes or LK induce macrophage activation for leishmanicidal activity, however, are not yet known. We analyzed interactions of leishmania amastigotes with human monocytes cultured in vitro as a nonadherent cell pellet. Leishmania donovani and L. major replicated in freshly isolated monocytes. Monocytes treated with greater than 200 IU/ml of the LK, human Interferon-gamma (IFN-gamma), destroyed tumor cells and L. donovani, but not L. major. Phorbol myristate acetate, endotoxic bacterial lipopolysaccharide, and recombinant human IFN-alpha and IFN-beta did not induce cytotoxicity. The time course for induction of cytotoxicity contrasted sharply with that of previously described monocyte antileishmanial activity: IFN-gamma induced cytotoxicity even when added after infection with L. donovani; induction of cytotoxicity did not require that IFN-gamma be present throughout the period of culture after infection: a 30-min preinfection pulse of IFN-gamma was sufficient to induce 70% of maximal activity; and freshly isolated monocytes and cells cultured for up to 4 days in vitro prior to infection and IFN-gamma treatment were equally responsive to IFN-gamma. These studies provide convincing evidence for intracellular cytotoxicity for L. donovani by freshly isolated human monocytes. This system provides an important base for further analysis of induction and expression of cytotoxic mechanisms against leishmania and other intracellular organisms that cause human disease.     

L-arginine metabolism during interaction of Trypanosoma cruzi with host cells

Trypanosoma cruzi invades a diversity of nucleated cells in the mammalian host. Macrophages are among the first cells to be parasitized and, after activation by inflammatory stimuli, they participate in the control of infection. However, some parasites manage to evade the immune response and establish a chronic infection in differentiated cells. L-arginine is located at the crossroads of divergent routes that produce metabolites, including nitric oxide and polyamines, which influence the outcome (i.e. resolution or progression) of infection. This article discusses the fate and actions of L-arginine-derived biomolecules formed both in the host and in the parasite during T. cruzi-host-cell interactions.     

Algorithm for prediction of reconvalescent salmonellosis carriage

Of total of 181 patients with Salmonella infection were examined by clinical and laboratory methods. As many as 124 indices characterizing biological properties of Salmonellae, a large intestine microbiocenosis status, systemic and local immunity, were investigated as well. Among these indices, the most revealing signs were defined to prognosticate the reconvalescent carrier state. Conclusion was made on the prevalence of immune mechanisms in the development of reconvalescent salmonella carriage and on the important role of the ability of a causative agent to inactivate the factors of host innate immunity in this process. Diagnostic prognosis algorithm for Salmonella bacterial carriage was worked out. Clinical testing confirmed its effectiveness.     

Cytokines inSalmonella infection

Before the onset of specific immune response, the host defence against Salmonella infection is regulated by cytokines characteristic for immunity to intracellular bacteria. Cytokine response to non-typhoidal Salmonellae is described.     

The trophoblast is a component of the innate immune system during pregnancy

Systemic infection with Listeria monocytogenes, a Gram-positive intracellular bacterium, has been used extensively to analyze the innate immune response. Macrophages are central to this response, acting as both the host for and principal defense against this bacterium. During pregnancy L. monocytogenes has a predilection for replication at the maternal-placental interface and consequently is an important cause of fetal morbidity and mortality. However, macrophages are mostly excluded from the murine placenta with neutrophils acting as the main immune effector cell against this bacterium. Colony stimulating factor (CSF)-1, a macrophage growth factor, is synthesized in high concentrations by the uterine epithelium during pregnancy, where it is targeted to trophoblast bearing CSF-1-receptors. To define the involvement of CSF-1 in placental immunity, we infected pregnant mice either homozygous or heterozygous for an inactivating recessive mutation in the gene for CSF-1 (osteopetrotic; Csfmop) with L. monocytogenes. CSF-1 was required to recruit neutrophils to the site of listerial infection in the decidua basalis, and infection by Listeria remained unrestrained in its absence. CSF-1 acted by inducing the trophoblast to synthesize the neutrophil chemoattractants (KC) and macrophage inflammatory protein (MIP)-2. Thus, during pregnancy, trophoblast responsive to CSF-1 acts to organize the maternal immune response to bacterial infection at the utero-placental interface. This previously unknown function indicates that the trophoblast acts as a pregnancy-specific component of the innate immune system.     

Alternative methods to limit extracellular bacterial activity for enumeration of intracellular bacteria

The gentamicin survival assay, a method routinely used to estimate bacterial infection of eukaryotic host cells, depends on the presumed limited penetration of gentamicin across the eukaryotic cell membrane. However, some studies have suggested that gentamicin may in fact enter eukaryotic cells and kill intracellular bacteria. In this study we devised alternative methods to enumerate intracellular Salmonellae using a lytic bacteriophage, SP6, and an amino acid auxotroph, Pro- mutant, which replicates selectively within host cells in the presence of its uptake inhibitor, 3,4-dehydro-L-proline. The conventional gentamicin survival assay was systematically compared with the alternative methods for the enumeration of intracellular Salmonellae. We found that gentamicin decreases the survival of intracellular Salmonellae when added to extracellular media at concentrations above 20 microg/ml. The alternative methods do not suffer from this disadvantage, suggesting that they should be used to replace the gentamicin survival assay. In addition, the proline auxotroph method could be applied to detect bacterial release from host cells.     

Role and function of macrophages in the metabolic syndrome

Macrophages are key innate immune effector cells best known for their role as professional phagocytes, which also include neutrophils and dendritic cells. Recent evidence indicates that macrophages are also key players in metabolic homoeostasis. Macrophages can be found in many tissues, where they respond to metabolic cues and produce pro- and/or anti-inflammatory mediators to modulate metabolite programmes. Certain metabolites, such as fatty acids, ceramides and cholesterol crystals, elicit inflammatory responses through pathogen-sensing signalling pathways, implicating a maladaptation of macrophages and the innate immune system to elevated metabolic stress associated with overnutrition in modern societies. The outcome of this maladaptation is a feedforward inflammatory response leading to a state of unresolved inflammation and a collection of metabolic pathologies, including insulin resistance, fatty liver, atherosclerosis and dyslipidaemia. The present review summarizes what is known about the contributions of macrophages to metabolic diseases and the signalling pathways that are involved in metabolic stress-induced macrophage activation. Understanding the role of macrophages in these processes will help us to develop therapies against detrimental effects of the metabolic syndrome.