Macrophage receptors and immune recognition

The scaffold MyD88 acts to couple protein kinase Cepsilon to Toll-like receptors

Mice lacking protein kinase Cepsilon (PKCepsilon) are hypersensitive to both Gram-positive and Gram-negative bacterial infections; however, the mechanism of PKCepsilon coupling to the Toll-like receptors (TLRs), responsible for pathogen detection, is poorly understood. Here we sought to investigate the mechanism of PKCepsilon involvement in TLR signaling and found that PKCepsilon is recruited to TLR4 and phosphorylated on two recently identified sites in response to lipopolysaccharide (LPS) stimulation. Phosphorylation at both of these sites (Ser-346 and Ser-368) resulted in PKCepsilon binding to 14-3-3beta. LPS-induced PKCepsilon phosphorylation, 14-3-3beta binding, and recruitment to TLR4 were all dependent on expression of the scaffold protein MyD88. In mouse embryo fibroblasts and activated macrophages from MyD88 knock-out mice, LPS-stimulated PKCepsilon phosphorylation was reduced compared with wild type cells. Acute knockdown of MyD88 in LPS-responsive 293 cells also resulted in complete loss of Ser-346 phosphorylation and TLR4/PKCepsilon association. By contrast, MyD88 overexpression in 293 cells resulted in constitutive phosphorylation of PKCepsilon. A general role for MyD88 was evidenced by the finding that phosphorylation of PKCepsilon was induced by the activation of all TLRs tested that signal through MyD88 (i.e. all except TLR3) both in RAW cells and in primary human macrophages. Functionally, it is established that phosphorylation of PKCepsilon at these two sites is required for TLR4- and TLR2-induced NFkappaB reporter activation and IkappaB degradation in reconstituted PKCepsilon(-/-) cells. This study therefore identifies the scaffold protein MyD88 as the link coupling TLRs to PKCepsilon recruitment, phosphorylation, and downstream signaling.

Expression and function of ephrin-B1 and its cognate receptor EphB2 in human atherosclerosis: from an aspect of chemotaxis

Although several cytokines and chemokines have been demonstrated to play pivotal roles in the pathophysiological conditions of atherosclerosis, few findings exist regarding the expression and function of cytokine-modulating molecules such as ephrin-Bs and their cognate receptors, EphBs, in human atherosclerosis. Therefore, in the present study, we screened novel genes modulating atherogenesis by cDNA array and quantitatively determined them by real-time RT (reverse transcription)-PCR in human carotid atherosclerotic plaques. Ephrin-B1 and EphB2, key regulators of embryogenesis, were significantly up-regulated in plaques compared with those in adjacent control tissues [ephrin-B1, 0.638+/-0.106 compared with 0.831+/-0.152, or 130% (P<0.05); EphB2, 1.296+/-0.281 compared with 2.233+/-0.506, or 172% (P<0.05)]. Immunohistological analysis demonstrated that both ephrin-B1 and EphB2 were expressed in macrophages and T-lymphocytes in plaques as well as in monocytes, T-lymphocytes and arterial endothelial cells isolated from healthy adults. Interestingly, the extracellular domains of ephrin-B1 and EphB2, the expression of which were both enhanced in stimulated THP-1 cells, significantly inhibited spontaneous (22.5 and 27.6% respectively; P<0.01) and MCP-1 (monocyte chemoattractant protein-1)-dependent (29.7 and 22.6% respectively; P<0.01) migration of monocytes. In conclusion, these results demonstrate that ephrin-B1 and EphB2 are overexpressed in atherosclerotic tissue and might locally regulate cell migration, possibly through modulating cytokine-related chemotaxic activity; however, the functional role of these molecules in atherogenesis should be investigated further.

Modulation of the immune responses in chickens by low-pathogenicity avian influenza virus H9N2

Most low-pathogenicity avian influenza (LPAI) viruses cause no or mild disease in avian species. Little is known about the mechanisms of host defence and the immune responses of avian influenza-infected birds. This study showed that chicken macrophages are susceptible to infection with LPAI H9N2 and H6N2 viruses and that infection led to apoptosis. In H9N2 virus-infected chicken macrophages, Toll-like receptor 7 responded to infection and mediated the cytokine responses. Whilst pro-inflammatory cytokines were largely upregulated, the interferon (IFN) response was fairly weak and IFN-inducible genes were differentially regulated. Among the regulated genes, major histocompatibility complex (MHC) antigens II were downregulated, which also occurred in the lungs of H9N2-infected chickens. Additionally, interleukin (IL)-4, IL-4 receptor and CD74 (MHC class II invariable chain) were also downregulated, all of which are pivotal in the activation of CD4+ helper T cells and humoral immunity. Remarkably, in H9N2 virus-infected chickens, the antibody response was severely suppressed. This was in contrast to the robust antibody response in chickens infected with H6N2 virus, in which expression of MHC class II antigens was upregulated. These data suggest that neutralizing antibodies and humoral immunity may not be developed efficiently in H9N2-infected chickens. These findings raise questions about how some LPAI viruses differentially regulate avian immune responses and whether they have similar effects on mammalian immune function.

CLEC9A is a novel activation C-type lectin-like receptor expressed on BDCA3+ dendritic cells and a subset of monocytes

We describe here the first characterization of CLEC9A, a group V C-type lectin-like receptor located in the “Dectin-1 cluster” of related receptors, which are encoded within the natural killer (NK)-gene complex. Expression of human CLEC9A is highly restricted in peripheral blood, being detected only on BDCA3⁺ dendritic cells and on a small subset of CD14⁺CD16^- monocytes. CLEC9A is expressed at the cell surface as a glycosylated dimer and can mediate endocytosis, but not phagocytosis. CLEC9A possesses a cytoplasmic immunoreceptor tyrosine-based activation-like motif that can recruit Syk kinase, and we demonstrate, using receptor chimeras, that this receptor can induce proinflammatory cytokine production. These data indicate that CLEC9A functions as an activation receptor.

Synthetic chemerin-derived peptides suppress inflammation through ChemR23

Chemerin is a chemotactic protein that binds to the G protein–coupled receptor, ChemR23. We demonstrate that murine chemerin possesses potent antiinflammatory properties that are absolutely dependent on proteolytic processing. A series of peptides was designed, and only those identical to specific C-terminal chemerin sequences exerted antiinflammatory effects at picomolar concentrations in vitro. One of these, chemerin15 (C15; A¹⁴⁰-A¹⁵⁴), inhibited macrophage (MΦ) activation to a similar extent as proteolyzed chemerin, but exhibited reduced activity as a MΦ chemoattractant. Intraperitoneal administration of C15 (0.32 ng/kg) to mice before zymosan challenge conferred significant protection against zymosan-induced peritonitis, suppressing neutrophil (63%) and monocyte (62%) recruitment with a concomitant reduction in proinflammatory mediator expression. Importantly, C15 was unable to ameliorate zymosan-induced peritonitis in ChemR23^−/− mice, demonstrating that C15's antiinflammatory effects are entirely ChemR23 dependent. In addition, administration of neutralizing anti-chemerin antibody before zymosan challenge resulted in a significant exacerbation of peritoneal inflammation (up to 170%), suggesting an important endogenous antiinflammatory role for chemerin-derived species. Collectively, these results show that chemerin-derived peptides may represent a novel therapeutic strategy for the treatment of inflammatory diseases through ChemR23.

Multiple sclerosis and Alzheimer's disease

OBJECTIVE

Chronic inflammation with microglia activation is thought to play a major role in the formation or clearance of Alzheimer's disease (AD) lesions, as well as in the induction of demyelination in multiple sclerosis (MS). In MS, the cortex is severely affected by chronic, long-lasting inflammation, microglia activation, and demyelination. To what extent chronic inflammation in the cortex of MS patients influences the development of AD lesions is so far unresolved.

METHODS

The study was performed on autopsy tissue of 45 MS cases, 9 AD cases, and 15 control subjects. We analyzed lymphocyte and plasma cell infiltration in relation to microglia activation, to the presence of beta-amyloid plaques and (AT8+) neurofibrillary tangles, and to myelin pathology.

RESULTS

Profound microglia activation, determined by a broad spectrum of markers, was found in both MS and AD cortices, and the patterns of microglia activation were closely similar. Microglia activation in MS cortex, in contrast with that in AD and control cortex, correlated with lymphocyte and plasma-cell infiltrates in the meninges. MS cases older than 64 years experienced development of AD pathology in comparable incidence as seen in the course of normal aging. The density of beta-amyloid plaques and neurofibrillary tangles did not differ between demyelinated and nondemyelinated cortical areas.

CONCLUSIONS

Our data suggest that microglia activation in the MS cortex alone has little or no influence on the development of cortical AD pathology.

Senescence regulates macrophage activation and angiogenic fate at sites of tissue injury in mice

Abnormal angiogenesis plays a key role in diseases of aging such as heart disease, certain cancers, and eye diseases including age-related macular degeneration. Macrophages have been shown previously to be both anti- and proangiogenic, and their role in regulating angiogenesis at sites of tissue injury is critical and complex. In this study, we analyzed cytokine gene expression patterns of mouse macrophages by real-time quantitative PCR and tested the functional effects of senescence on gene expression and macrophage polarization. Following laser injury to the retina, IL-10 was upregulated and Fas ligand (FasL), IL-12, and TNF-alpha were downregulated in ocular macrophages of old mice (>18 months of age). Downregulation of FasL on macrophages led to a loss of the antiangiogenic phenotype, as evidenced by the inability of these macrophages to inhibit vascular endothelial cells. Our results demonstrate that senescence, FasL, and IL-10 are key determinants of macrophage function that alter the growth of abnormal postdevelopmental blood vessels in disease processes including blinding eye disease.

Osteoclasts - the innate immune cells of the bone

Osteopenia and periarticular bony erosion are consequences of chronic inflammatory autoimmune disease due to an imbalance of osteoclast activity relative to new bone formation. Osteoclasts, which are specialized as the only bone resorbing cell type, are differentiated from hematopoietic myeloid precursor cells. Inflammatory signals mediated by multiple types of immune cells and cytokines have significant influence over osteoclast differentiation and function through direct effects on osteoclast precursors and indirect effects via osteoblasts and other cells in the bony microenvironment including synovial cells, stromal cells, osteocytes and chondrocytes. Recent studies have demonstrated that osteoclasts themselves express a number of immune receptors and are regulated similarly to macrophages and dendritic cells, closely related cells in the innate immune system. Though we are only beginning to understand the roles of innate immune receptors in osteoclasts, some of these receptors have been shown to be critical regulators of differentiation and function of osteoclasts. Osteoclasts likely function as the innate immune cells of the bone, thus are highly regulated to appropriately respond to stress and inflammatory changes in their microenvironment.

BDCA2/Fc epsilon RI gamma complex signals through a novel BCR-like pathway in human plasmacytoid dendritic cells

Dendritic cells are equipped with lectin receptors to sense the extracellular environment and modulate cellular responses. Human plasmacytoid dendritic cells (pDCs) uniquely express blood dendritic cell antigen 2 (BDCA2) protein, a C-type lectin lacking an identifiable signaling motif. We demonstrate here that BDCA2 forms a complex with the transmembrane adapter FcɛRIγ. Through pathway analysis, we identified a comprehensive signaling machinery in human pDCs, similar to that which operates downstream of the B cell receptor (BCR), which is distinct from the system involved in T cell receptor (TCR) signaling. BDCA2 crosslinking resulted in the activation of the BCR-like cascade, which potently suppressed the ability of pDCs to produce type I interferon and other cytokines in response to Toll-like receptor ligands. Therefore, by associating with FcɛRIγ, BDCA2 activates a novel BCR-like signaling pathway to regulate the immune functions of pDCs.

Dendritic cells (DCs) are specialized sentinels in the immune system that detect invading pathogens and, upon activation, initiate immune responses. DCs express C-type lectin receptors on their surface, which facilitate antigen capture. A distinct population of DCs, called plasmacytoid DCs (pDCs), display an extraordinary ability to rapidly make huge amounts of antiviral interferon (IFN) against viral infections. Human pDCs uniquely express a C-type lectin named BDCA2 that potently regulates pDCs function, yet the mechanism of how BDCA2 transduces signals is unknown. We show here that BDCA2 forms a complex with the transmembrane adapter FcɛRIγ. Using signaling pathway analysis, we discovered a comprehensive signaling machinery in human pDCs, similar to that which operates downstream of B cell receptors (BCRs), but distinct from the pathway involved in T cell receptor signaling. By associating with FcɛRIγ, BDCA2 activates a novel BCR-like signaling pathway to regulate the immune functions of pDCs. Since several pDC receptors use this pathway to modulate IFN and cytokine responses, these findings will guide more studies on how pDCs are regulated. Such mechanisms may lead to potential therapeutic interventions in autoimmune diseases involving hyperactivated pDCs, such as systemic lupus erythematosus and psoriasis.

Plasmacytoid dendritic cells (pDCs) are renowned for their production of type 1 interferon in response to viral infection, which is signified by Toll-like receptor (TLR) activation. Here, blood dendritic cell antigen 2(BDCA2), a C-type lectin receptor expressed uniquely on pDCs, is shown to block the ultimate effectors of TLR signaling via a novel pathway.

LPS reduces HIV-1 replication in primary human macrophages partly through an endogenous production of type I interferons

It has been proposed that the systemic immune activation state seen in HIV-1-infected patients is caused by circulating microbial products such as lipopolysaccharide (LPS). Given that macrophages play a key role in HIV-1 pathogenesis, we investigated the LPS-mediated effect on HIV-1 replication in cells of the myeloid lineage. We demonstrate that LPS promotes virus gene expression in a monocytic cell line while it diminishes virus production in primary human monocyte-derived macrophages (MDM). The incapacity of LPS to drive HIV-1 production in MDM was not due to its inability to activate the ubiquitous transcription factor NF-kappaB even in virus-infected cells. Neutralization of type I interferons (IFN) with B18R, a soluble vaccinia virus-coded type I IFN receptor, significantly but not totally diminished the antiviral activity of LPS. Therefore, inhibition of HIV-1 replication in MDM treated with microbial-derived LPS resulted from the induction of type I interferons and a yet to be defined soluble factor.

Angiogenesis in eye disease: immunity gained or immunity lost?

The anti-inflammatory nature of the intraocular environment is critical to the immune privilege of the eye. An important part of immune privilege is the induction of apoptosis by two death-inducing ligands (FasL and TRAIL) that can limit the spread of inflammation and control tumor growth. While initial studies focused on control of inflammation and the impact of these molecules on the systemic immune response, more recent studies have extended this concept to pathogenic neovascularization. This process is an important component of several blinding eye disorders including age-related macular degeneration, diabetic retinopathy, retinopathy of prematurity, and corneal disease. These studies showed that the mediators of immune privilege also regulate the extent of angiogenesis. In this article, we will develop the idea that constitutive expression of FasL in the eye, as well as inducible FasL on cells of the immune system, modulates neovascularization in ocular disease. Further, we will present the idea that macrophage participation in this process and their function during disease depends on the microenvironment and the cytokine milieu. These concepts challenge the idea that neovascular eye disease is simply an inflammatory process and support the idea that these diseases may result from the loss or dysfunction of important components of the cellular immune system.

Interleukin-32 induces the differentiation of monocytes into macrophage-like cells

After emigration from the bone marrow to the peripheral blood, monocytes enter tissues and differentiate into macrophages, the prototype scavenger of the immune system. By ingesting and killing microorganisms and removing cellular debris, macrophages also process antigens as a first step in mounting a specific immune response. IL-32 is a cytokine inducing proinflammatory cytokines and chemokines via p38-MAPK and NF-kappaB. In the present study, we demonstrate that IL-32 induces differentiation of human blood monocytes as well as THP-1 leukemic cells into macrophage-like cells with functional phagocytic activity for live bacteria. Muramyl dipepide (MDP), the ligand for the intracellular nuclear oligomerization domain (NOD) 2 receptor, has no effect on differentiation alone but augments the monocyte-to-macrophage differentiation by IL-32. Unexpectedly, IL-32 reversed GM-CSF/IL-4-induced dendritic cell differentiation to macrophage-like cells. Whereas the induction of TNFalpha, IL-1beta, and IL-6 by IL-32 is mediated by p38-MAPK, IL-32-induced monocyte-to-macrophage differentiation is mediated through nonapoptotic, caspase-3-dependent mechanisms. Thus, IL-32 not only contributes to host responses through the induction of proinflammatory cytokines but also directly affects specific immunity by differentiating monocytes into macrophage-like cells.

Integrin beta 1 regulates phagosome maturation in macrophages through Rac expression

Phagocytosis and subsequent phagosome maturation by professional phagocytes are essential in the clearance of infectious microbial pathogens. The molecular regulation of phagosome maturation is largely unknown. We show that integrin beta(1) plays critical roles in the phagocytosis of microbial pathogens and phagosome maturation. Macrophages lacking integrin beta(1) expression exhibit reduced phagocytosis of bacteria, including group B streptococcus and Staphylococcus aureus. Furthermore, phagosomes from macrophages lacking integrin beta(1) show lowered maturation rate, defective acquisition of lysosome membrane markers, and reduced F-actin accumulation in the periphagosomal region. Integrin beta(1)-deficient macrophages exhibit impaired bactericidal activity. We found that the expression of the Rho family GTPases Rac1, Rac2, and Cdc42 was reduced in integrin beta(1)-deficient macrophages. Ectopic expression of Rac1, but not Cdc42, in integrin beta(1)-deficient macrophages restored defective phagosome maturation and F-actin accumulation in the periphagosomal region. Importantly, macrophages lacking Rac1/2 also exhibit defective maturation of phagosomes derived from opsonized Escherichia coli or IgG beads. Taken together, these results suggest that integrin beta(1) regulates phagosome maturation in macrophages through Rac expression.

Indirect macrophage responses to ionizing radiation: implications for genotype-dependent bystander signaling

In addition to the directly mutagenic effects of energy deposition in DNA, ionizing radiation is associated with a variety of untargeted and delayed effects that result in ongoing bone marrow damage. Delayed effects are genotype dependent with CBA/Ca mice, but not C57BL/6 mice, susceptible to the induction of damage and also radiation-induced acute myeloid leukemia. Because macrophages are a potential source of ongoing damaging signals, we have determined their gene expression profiles and we show that bone marrow-derived macrophages show widely different intrinsic expression patterns. The profiles classify macrophages derived from CBA/Ca mice as M1-like (pro-inflammatory) and those from C57BL/6 mice as M2-like (anti-inflammatory); measurements of NOS2 and arginase activity in normal bone marrow macrophages confirm these findings. After irradiation in vivo, but not in vitro, C57BL/6 macrophages show a reduction in NOS2 and an increase in arginase activities, indicating a further M2 response, whereas CBA/Ca macrophages retain an M1 phenotype. Activation of specific signal transducer and activator of transcription signaling pathways in irradiated hemopoietic tissues supports these observations. The data indicate that macrophage activation is not a direct effect of radiation but a tissue response, secondary to the initial radiation exposure, and have important implications for understanding genotype-dependent responses and the mechanisms of the hemotoxic and leukemogenic consequences of radiation exposure.

Bridging effect of recombinant human mannose-binding lectin in macrophage phagocytosis of Escherichia coli

Mannose-binding lectin (MBL) exists in the serum as a complex with MBL-associated serine protease (MASP). A recent paper described how MASP-free recombinant rat MBL stimulates the phagocytosis of Escherichia coli and Staphylococcus aureus by rat Kupffer cells through an increase in the level of a phagocytosis receptor. We have examined the effect of human MBL on the phagocytic action of human macrophages. Purified recombinant human MBL stimulated the phagocytosis of E. coli by THP-1 macrophages, leaving that of latex beads, apoptotic human cells, zymosan particles or S. aureus unchanged. This stimulatory effect was observed when either phagocytes or targets were preincubated with MBL. Furthermore, MBL bound to THP-1 macrophages as well as to E. coli, but not to S. aureus, through lipid A. These results indicated that human MBL in the absence of MASP stimulates macrophage phagocytosis of E. coli by bridging targets and phagocytes.

The biological role of dectin-1 in immune response

The identification of antigen-recognizing receptors in the innate immune system significantly helped us to understand the initiation and regulation of the innate immune response. Dectin-1 was recently identified as the most important receptor for beta-glucan. Recognition of beta-glucan by dectin-1 triggers effective immune response, including phagocytosis and proinflammatory factor production, to eliminate infecting fungi, which especially benefits immunocompromised patients against opportunistic fungal infection. In addition, dectin-1 is involved in the adaptive immune response as well as autoimmune diseases and immune tolerance. In this paper, we will mainly focus on the characteristics of dectin-1 and its biological role in immune response.

Molecular pathogenesis of Shigella spp.: controlling host cell signaling, invasion, and death by type III secretion

Shigella spp. are gram-negative pathogenic bacteria that evolved from harmless enterobacterial relatives and may cause devastating diarrhea upon ingestion. Research performed over the last 25 years revealed that a type III secretion system (T3SS) encoded on a large plasmid is a key virulence factor of Shigella flexneri. The T3SS determines the interactions of S. flexneri with intestinal cells by consecutively translocating two sets of effector proteins into the target cells. Thus, S. flexneri controls invasion into EC, intra- and intercellular spread, macrophage cell death, as well as host inflammatory responses. Some of the translocated effector proteins show novel biochemical activities by which they intercept host cell signal transduction pathways. An understanding of the molecular mechanisms underlying Shigella pathogenesis will foster the development of a safe and efficient vaccine, which, in parallel with improved hygiene, should curb infections by this widespread pathogen.

Glial toll-like receptor signaling in central nervous system infection and autoimmunity

Innate immunity in the CNS depends primarily on the functions of glial cells, astrocytes and microglia, which are important for the early control of pathogen replication and direct the recruitment and activation of cells of the adaptive immune system required for pathogen clearance. Efficient immune responses are required for clearance of an invading pathogen, but dysregulation of a pro-inflammatory response in the CNS could lead to the development of autoimmunity. This review summarizes the activation of toll-like receptors (TLRs) expressed on glial cells and the functional outcome of these interactions for CNS health and disease which depends on a delicate balance of the protective and toxic effects of molecules induced in the CNS following TLR ligation.

The biodegradability of electrospun Dextran/PLGA scaffold in a fibroblast/macrophage co-culture

Fibroblast and macrophage are 2 dominant cell types respond cooperatively to degrade implanted biomaterials. Using an electrospun Dextran/Poly-lactide-co-glycolide (PLGA) scaffold as a model, an in vitro fibroblast/macrophage co-culture system was developed to investigate the degradability of implantable biodegradable materials. SEM showed that both fibroblasts and macrophages were able to degrade the scaffold, separately or cooperatively. Under the synergistic coordination of macrophages and fibroblasts, scaffolds showed faster degradation rate than their counterparts incubated with a single type of cells as well as in PBS or cell culture medium. Lysozyme, non-specific esterase (NSE), gelatinase, hyaluronidase-1 and alpha-glucosidase were up-regulated in the presence of the scaffold, suggesting their roles in the cell-mediated scaffold degradation. In addition, the expressions of cell surface receptors CD204 and Toll like receptor 4 (TLR4) were elevated 1 week after cell seeding, implying that these receptors might be involved in scaffold degradation. The results of in vivo subdermal implantation of the scaffold further confirmed the biodegradability of the Dextran/PLGA scaffold. The fibroblast/macrophage co-culture model adequately mimicked the in vivo environment and could be further developed into an in vitro tool for initial biomaterial evaluation.

The macrophage: past, present and future

As we approach the centenary of Elie Metchnikoff's Nobel Prize (1908), it is opportune to reflect upon the history of macrophage immunobiology, take stock of current knowledge and anticipate questions for the future. Starting from his appreciation of phagocytosis as an important determinant of host defence against infection and injury, we have learned a great deal about the distribution of macrophages throughout the body, their heterogeneous phenotype and complex functions in tissue homeostasis as well as in innate and acquired immunity. Recent discoveries of Toll-like and other plasma membrane, vacuolar and cytosolic recognition molecules have brought the macrophage and closely related dendritic cells to the centre of immunologic attention, but many earlier discoveries of their cellular and molecular properties have laid a broader foundation to the appreciation of their remarkable plasticity and adaptability to local and systemic cues. Discoveries of pro-inflammatory mediators such as TNF and other secretory products have provided valuable insights into the role of macrophages in many acute and chronic disease processes, and led to the development of effective therapeutics. Much remains to be discovered regarding both their specific functions and by study of their general cellular properties, in vitro and in vivo.

Immunotherapy of metastatic breast cancer patients with vitamin D-binding protein-derived macrophage activating factor (GcMAF)

Serum vitamin D3-binding protein (Gc protein) is the precursor for the principal macrophage activating factor (MAF). The MAF precursor activity of serum Gc protein of breast cancer patients was lost or reduced because Gc protein was deglycosylated by serum alpha-N-acetylgalactosaminidase (Nagalase) secreted from cancerous cells. Patient serum Nagalase activity is proportional to tumor burden. The deglycosylated Gc protein cannot be converted to MAF, resulting in no macrophage activation and immunosuppression. Stepwise incubation of purified Gc protein with immobilized beta-galactosidase and sialidase generated probably the most potent macrophage activating factor (termed GcMAF) ever discovered, which produces no adverse effect in humans. Macrophages treated in vitro with GcMAF (100 pg/ml) are highly tumoricidal to mammary adenocarcinomas. Efficacy of GcMAF for treatment of metastatic breast cancer was investigated with 16 nonanemic patients who received weekly administration of GcMAF (100 ng). As GcMAF therapy progresses, the MAF precursor activity of patient Gc protein increased with a concomitant decrease in serum Nagalase. Because of proportionality of serum Nagalase activity to tumor burden, the time course progress of GcMAF therapy was assessed by serum Nagalase activity as a prognostic index. These patients had the initial Nagalase activities ranging from 2.32 to 6.28 nmole/min/mg protein. After about 16-22 administrations (approximately 3.5-5 months) of GcMAF, these patients had insignificantly low serum enzyme levels equivalent to healthy control enzyme levels, ranging from 0.38 to 0.63 nmole/min/mg protein, indicating eradication of the tumors. This therapeutic procedure resulted in no recurrence for more than 4 years.

Modulation of P2X7 receptor expression in macrophages from mineral oil-injected mice

P2X7 receptor activation is involved in a number of pro-inflammatory responses in macrophages and other immune cells. Their expression can be positively modulated with lipopolysaccharide (LPS) and TNFalpha, reinforcing their role during inflammation. We investigated the effect of substances capable of recruiting macrophages into the peritoneal cavity of mice (mineral oil and thioglycolate) on P2X7 receptor expression and function, addressing whether these stimuli can interfere with multinucleated giant cell (MGC) formation, ATP-induced apoptosis, plasma membrane permeabilization and nitric oxide production. It was demonstrated that mineral oil treatment reduces P2X7-dependent MGC formation, whereas thioglycolate treatment does not. Mineral oil treatment reduced P2X7 receptor expression, down-modulating ATP-induced apoptosis, permeabilization and nitric oxide production. In conclusion, mineral oil down modulated P2X7 expression and consequently P2X7-associated phenomena, but thioglycolate did not. These effects might be associated with the unpleasant side effects already described during long-term administration of mineral oil for cosmetic purposes or as a laxative and could be useful in understanding the mechanism of recycling and modulation of P2 receptors present in other situations of immunopathological interest.

Comparability and monitoring immunogenic N-linked oligosaccharides from recombinant monoclonal antibodies from two different cell lines using HPLC with fluorescence detection and mass spectrometry

One of the most important structural features of recombinant monoclonal antibodies produced in mammalian cells is the N-linked oligosaccharide profile. These profiles impact recombinant therapeutics in a multitude of ways affecting distribution, efficacy, and immunogenicity. High mannose, alpha-gal and other oligosaccharide species are highly immunogenic and in most cases should be minimized during manufacturing. A recombinant monoclonal antibody, h5G1.1, was produced in NS0 and CHO cell lines and tested to identify changes in the N-linked oligosaccharide profiles caused from a change in cell line. Traditional peak analysis using HPLC with fluorescence detection was augmented by mass spectrometric analysis. Nano LC-MS following tryptic digestion corroborated HPLC findings of the presence of several alpha-gal oligosaccharide species in the recombinant IgG (rIgG) from NS0 cell line. Both cell lines possessed rIgGs with complex and small amounts of high mannose glycans.

Fungal Recognition by TLR2 and Dectin-1

The innate immune system utilizes multiple receptors to recognize fungal pathogens, and the net inflammatory response is controlled by interactions between these receptors. Many fungi are recognized, at least in part, by Toll-like receptor 2 (TLR2) and Dectin-1. Examination of the roles these receptors play together and on their own is a useful model for understanding the interplay between innate immune receptors. This review focuses on the role(s) of TLR2 and Dectin-1 in triggering inflammatory responses, transcription factor activation, phagocytosis, and reactive oxygen production in response to fungi.

Macrophage fusion: molecular mechanisms

Macrophages are the most versatile, plastic, and mobile cells in the animal kingdom. They are present in all tissues and might even define a true " body-wide" network that maintains health and ensures the repair of tissues and organs. In specific and rare instances, macrophages fuse to form multinucleate osteoclasts and giant cells in bone and in chronic inflammatory reactions, respectively. While macrophages lose most of their plasticity and mobility after they become multinucleate, at the same time they acquire the capacity to resorb calcified tissues, such as bone, and foreign bodies, such as pathogens and implants, and they mediate the replacement of the resorbed tissue by new tissue. There is evidence to suggest that macrophages might also fuse with somatic cells to repair tissues and with tumor cells to trigger the metastatic process. The molecular machinery of macrophage fusion remains poorly characterized, but it is likely to be shared by all fusing macrophages.

Murine macrophages: a technical approach

In this chapter, we describe current protocols used for the characterization of macrophages (MPhi) in mouse tissues and in cell suspensions from spleen and lymph nodes. Also, we include a brief description of a complementary approach: culture of primary MPhi. Although culture MPhi are extremely useful for analysing the basic biology of MPhi and their receptors, it should not be forgotten that the term MPhi encompasses a wide range of different types of cells with phenotypic characteristics dependent on their activation state and tissue of origin. In our view, there is no perfect MPhi marker and analysis of the expression profile of several markers, and functional studies are required to make an informed guess of the cellular characteristics and function of the MPhi population of interest.

Lung Defenses

We breathe to live, but the air we breathe carries many potentially harmful agents. To protect us against these constant challenges, our lungs have defenses that are remarkably effective, biologically complex, and scientifically fascinating. It is not hyperbole to say that the pathogenesis of most lung disease begins with a breach of these defenses. This chapter surveys these normal lung defense systems. Just as this text assumes familiarity with general pathology, we also assume knowledge of basic immunology. This chapter emphasizes the lung’s variations on themes of innate and adaptive immunity, and discusses the special role of granulomatous inflammation in lung defenses.

Phagocytotic activation of muscularis resident macrophages inhibits smooth muscle contraction in rat ileum

Intestinal muscularis resident macrophages distributed in myenteric region may play an important role in the immunological host defense against infection. In this study, we investigated the phagocytic stimulation of resident macrophages on cyclooxygenase-2 (COX-2) expression and smooth muscle contraction in the small intestine of rat. After the injection of FITC-dextran to rat, phagocytosed macrophages could be detected in the myenteric plexus. FITC-positive macrophages were also immunostained with COX-2 antibody. The number of COX-2 immunopositive cells increased in a time-dependent manner reaching its maximum at 4 hr after the injection, which then decreased gradually but considerable number of cells were still remained on 7 days. The injection of FITC-dextran, however, did not change the population of ED2-positive resident macrophages even on 7 days. Production of PGE2 was significantly higher in the dextran treated tissue as compared to control tissue. In the smooth muscle tissue phagocytosed dextran, carbachol-induced contraction was significantly decreased. The suppression of the carbachol-induced contraction was completely restored by COX inhibitor, indomethacin. Finally we demonstrated that, in freshly isolated macrophage cells, addition of dextran induced a slow and sustained increase in intracellular Ca2+ concentration. These results indicate that phagocytotic activation of muscularis resident macrophages induces COX-2 gene expression and then results in production of PGE2 to suppress the smooth muscle contractile activity.

Innate immunity, macrophage activation, and atherosclerosis

Inflammation underpins the development of atherosclerosis. Initiation and progression of vascular inflammation involves a complex cellular network, with macrophages as major contributors. Activated macrophages produce proinflammatory mediators, bridge innate and adaptive immunity, regulate lipid retention, and participate directly in vascular repair and remodeling. Recent efforts to elucidate molecular mechanisms involved in the regulation of vascular inflammation in atherosclerosis have implicated several families of innate immune recognition receptors in inflammatory activation during the course of this disease. This article reviews our current understanding of innate immune recognition receptors, signaling pathways, and putative ligands implicated in activation of macrophages in the disease. In its final section, we propose a model for the role of macrophages in bridging inflammation and atherosclerosis from the perspective of innate immune recognition and activation.

Macrophages from 11beta-hydroxysteroid dehydrogenase type 1-deficient mice exhibit an increased sensitivity to lipopolysaccharide stimulation due to TGF-beta-mediated up-regulation of SHIP1 expression

11beta-Hydroxysteroid dehydrogenase type 1 (11betaHSD1) performs end-organ metabolism of glucocorticoids (GCs) by catalyzing the conversion of C(11)-keto-GCs to C(11)-hydroxy-GCs, thereby generating activating ligands for the GC receptor. In this study, we report that 11betaHSD1(-/-) mice are more susceptible to endotoxemia, evidenced by increased weight loss and serum TNF-alpha, IL-6, and IL-12p40 levels following LPS challenge in vivo. Peritoneal and splenic macrophage (splnMphi) from these genetically altered mice overproduce inflammatory cytokines following LPS stimulation in vitro. Inflammatory cytokine overexpression by 11betaHSD1(-/-) splnMphi results from an increased activation of NF-kappaB- and MAPK-signaling cascades and an attenuated PI3K-dependent Akt activation. The expression of SHIP1 is augmented in 11betaHSD1(-/-) Mphi and contributes to inflammatory cytokine production because overexpression of SHIP1 in primary bone marrow Mphi (BMMphi) leads to a similar type of hyperresponsiveness to subsequent LPS stimulation. 11betaHSD1(+/+) and 11betaHSD1(-/-) BMMphi responded to LPS similarly. However, 11betaHSD1(-/-) BMMphi derived in the presence of elevated GC levels up-regulated SHIP1 expression and increased their capacity to produce inflammatory cytokines following their activation with LPS. These observations suggest the hyperresponsiveness of 11betaHSD1(-/-) splnMphi results from myeloid cell differentiation in the presence of moderately elevated GC levels found within 11betaHSD1(-/-) mice. GC-conditioning of BMMphi enhanced SHIP1 expression via up-regulation of bioactive TGF-beta. Consistently, TGF-beta protein expression was increased in unstimulated CD11b(-) cells residing in the BM and spleen of 11betaHSD1(-/-) mice. Our results suggest that modest elevations in plasma GC levels can modify the LPS responsiveness of Mphi by augmenting SHIP1 expression through a TGF-beta-dependent mechanism.

Regulation of TREM expression in hepatic macrophages and endothelial cells during acute endotoxemia

Triggering receptor expressed on myeloid cells (TREM) regulates inflammatory responses to lipopolysaccharide (LPS). In these studies, we analyzed the expression of TREM in hepatic macrophages and endothelial cells which play a central role in LPS clearance. LPS administration to C3H/HeOuJ mice resulted in a rapid induction of TREM-1 and TREM-3, but a decrease in TREM-2 in liver macrophages and endothelial cells. The observation that TREM family members are detectable in endothelial cells is novel and demonstrates that their expression is not limited to myeloid cells. LPS-induced alterations in TREM expression were not evident in cells from C3H/HeJ TLR-4 mutant mice, indicating that the response is dependent on TLR-4. IL-1beta and TNFalpha upregulated TREM-1 and TREM-3 expression and suppressed TREM-2 expression in macrophages and endothelial cells. This activity involved PI3-kinase and p38 MAP kinase signaling. Interestingly, no significant differences were noted in TREM expression between wild-type and TNFR1-/- mice treated with LPS. Treatment of macrophages and endothelial cells with LPS upregulated expression of nitric oxide synthase-2 (NOS-2). This was blocked by TREM-1 Fc/fusion protein, indicating that TREM-1 mediates LPS-induced NOS-2 expression. These results suggest that TREM proteins are important in the inflammatory response of hepatic macrophages and endothelial cells to acute endotoxemia.

Invasive Candida species disease in infants and children: occurrence, risk factors, management, and innate host defense mechanisms

PURPOSE OF REVIEW

Invasive infections by opportunistic Candida species significantly impact morbidity and mortality. This review provides an update of the incidence, risk factors, and management of invasive candidal disease in infants and children, focusing on very-low-birth-weight neonates, and highlights recent advances in understanding candidal virulence factors and innate anti-Candida species host defense mechanisms.

RECENT FINDINGS

Invasive infections with Candida species are the most common cause of late-onset, blood culture-proven nosocomial sepsis in very-low-birth-weight neonates. Risk factors include colonization, long stay in neonatal intensive care units, and use of broad-spectrum antibiotics, central venous catheters, parenteral nutrition, and mechanical ventilation. These risks are compounded by increasing resistance of Candida species to standard antifungal agents. Recent data suggest that, in addition to the macrophage mannose receptor, beta-glucan receptors, Toll-like receptors, and galectin-3 play an important role in host recognition of Candida species.

SUMMARY

Reduction of proven risk factors, more aggressive eradication of colonizing fungi by anticandidal agents, and possibly Candida species vaccines may reduce Candida species-associated morbidity and mortality. Accumulating data of molecular mechanisms that underlie innate immune functions against Candida species may provide a basis to prevent and treat candidal infections more efficiently.

EMR1, the human homolog of F4/80, is an eosinophil-specific receptor

The EGF-TM7 F4/80 is a defining marker of murine macrophage populations. Applying flow cytometric analysis using the newly generated mAb A10, and quantitative real-time PCR, we here report the surprising observation that the human ortholog of F4/80, EGF-like module containing mucin-like hormone receptor (EMR)1, is absent on mononuclear phagocytic cells including monocytes, macrophages, and myeloid dendritic cells. Unexpectedly, we found that EMR1 expression is restricted to eosinophilic granulocytes, where expression is overlapping with the eotaxin receptor CCR3 and the immunoglobulin-like lectin Siglec-8. Absence on other leukocytes, including basophils, implies that EMR1 is a highly specific marker for eosinophils in humans.

Exogenous heat shock protein 27 uniquely blocks differentiation of monocytes to dendritic cells

Circulating heat shock protein (HSP)-27 is associated with tumor progression and increased post-injury infection. Extracellular HSP-27 might alter monocyte (MO)-derived DC and/or MPhi function to mediate immunosuppression. HSP-27 treatment inhibited expression of CD1a and CD1b/c, antigen uptake, and allogeneic T cell induction (MLR) by IL-4 + GM-CSF-differentiated human DC while increasing some MPhi characteristics ( upward arrowCD14, upward arrowCD16, upward arrowCD163). MO cytokine receptor profiles elicited by 24-h exogenous HSP-27 treatment remained supportive of immature DC (iDC) emergence ( upward arrowIL-4R, downward arrowIL-6R, downward arrowM-CSFR). IL-10, IL-6, and M-CSF (which promote MPhi differentiation) were significantly increased in IL-4 + GM-CSF + HSP-27 MO-->iDC differentiation cultures. However, HSP-27 treatment during MO differentiation to DC increased programmed cell death ligand 1 coinhibitor and depressed CD86 costimulator expression in parallel to decreased iDC MLR activity. This suggested that increased MPhi differentiation was not solely responsible for HSP-27 reduction of differentiating DC activity. HSP-27 treatment actually depressed the phagocytic capacity of MO differentiated to MPhi by IL-10 or M-CSF culture. CD163 (hemoglobin receptor) expression was depressed on M-CSF + HSP-27 MO-derived MPhi. HSP-27-mediated inhibition of MO-->iDC differentiation was reversed by p38alpha & beta inhibitor (SB202190) addition or TLR4 receptor modulation. HSP-27 impaired appropriate MO-->iDC and MO-->MPhi differentiation modulating expression of receptors necessary for their proper functions. This suggests that endogenous HSP-27 has immunoregulatory activities which could contribute to immunopathology.

Gene signatures reflect the marked heterogeneity of tissue-resident macrophages

Tissue-resident macrophages play an important role in defense against pathogens and perform key functions in organ homeostasis, innate and adaptive immunity. Tissue macrophages originate from blood monocytes that infiltrate virtually every organ in the body. Macrophages in different tissues share many characteristics, including their ability to migrate, phagocytose particles, metabolize lipids and present antigens. Morphologically they are quite heterogeneous, and some distinct functions have been reported. The gene expression profile of macrophages is reflective of both their shared and distinct biological functions. Here, we show that macrophages from murine spleen, liver and peritoneum display dramatically different expression profiles. Clusters of genes were found to represent unique biological functions related to adhesion, antigen presentation, phagocytosis, lipid metabolism and signal transduction. Some gene families, such as integrins, are differentially expressed among the macrophages resident in different tissues, suggesting that the tissue of residence influences their biological function.

Dectin-1 interaction with Mycobacterium tuberculosis leads to enhanced IL-12p40 production by splenic dendritic cells

Dectin-1 is a fungal pattern recognition receptor that binds to beta-glucans and triggers cytokine production by facilitating interaction with TLR2 or by directly activating spleen tyrosine kinase (Syk). To assess the possible role of Dectin-1 in the innate response to mycobacteria, we used an in vitro system in which IL-12p40 production is measured in splenic dendritic cells (SpDC) following exposure to live Mycobacterium tuberculosis bacilli. Treatment of SpDC with laminarin or glucan phosphate, two molecules known to block Dectin-1-dependent activity, led to a reduction in M. tuberculosis-induced IL-12p40 as well as IL-12p70 production. Moreover, SpDC from Dectin-1-/- chimeric mice displayed reduced IL-12p40 production in response to mycobacteria when compared with Dectin-sufficient DC. Laminarin treatment also inhibited mycobacterial-induced IL-12p40 production in DC from TLR2-/- mice, arguing that Dectin-1 functions independently of TLR2 signaling in this system. Importantly, a Dectin-1 fusion protein was found to directly bind to live mycobacteria in a laminarin-inhibitable manner indicating the presence of ligands for the receptor in the bacterium and laminarin pretreatment resulted in reduced association of mycobacteria to SpDC. In additional experiments, mycobacterial stimulation was shown to be associated with increased phosphorylation of Syk and this response was inhibited by laminarin. Furthermore, pharmacologic inhibition of Syk reduced the M. tuberculosis-induced IL-12p40 response. Together, these findings support a role for Dectin-1 in promoting M. tuberculosis-induced IL-12p40 production by DC in which the receptor augments bacterial-host cell interaction and enhances the subsequent cytokine response through an unknown mechanism involving Syk signaling.

Wound healing is impaired in MyD88-deficient mice: a role for MyD88 in the regulation of wound healing by adenosine A2A receptors

Synergy between Toll-like receptor (TLR) and adenosine A2A receptor (A2AR) signaling switches macrophages from production of inflammatory cytokines such as tumor necrosis factor-alpha to production of the angiogenic growth factor vascular endothelial growth factor (VEGF). We show in this study that this switch critically requires signaling through MyD88, IRAK4, and TRAF6. Macrophages from mice lacking MyD88 (MyD88(-/-)) or IRAK4 (IRAK4(-/-)) lacked responsiveness to TLR agonists and did not respond to A2AR agonists by expressing VEGF. Suppression of TRAF6 expression with siRNA in RAW264.7 macrophages also blocked their response to TLR and A2AR agonists. Excisional skin wounds in MyD88(-/-) mice healed at a markedly slower rate than wounds in wild-type MyD88(+/+) mice, showing delayed contraction, decreased and delayed granulation tissue formation, and reduced new blood vessel density. Although macrophages accumulated to higher levels in MyD88(-/-) wounds than in controls, expression of VEGF and HIF1-alpha mRNAs was elevated in MyD88(+/+) wounds. CGS21680, an A2AR agonist, promoted repair in MyD88(+/+) wounds and stimulated angiogenesis but had no significant effect on healing of MyD88(-/-) wounds. These results suggest that the synergistic interaction between TLR and A(2A)R signaling observed in vitro that switches macrophages from an inflammatory to an angiogenic phenotype also plays a role in wound healing in vivo.

Resveratrol modulates phagocytosis of bacteria through an NF-kappaB-dependent gene program

Many studies have shown that the pharmacological effects of resveratrol, a phytoalexin polyphenolic compound, include protective effects against cancer and inflammation as well as enhancement of stress resistance. In this study, we examined whether resveratrol affected the phagocytosis of bacteria by macrophages and the activation of the transcription factor NF-kappaB after stimulation with or without the ligand FSL-1 for Toll-like receptor 2 (TLR2). Phagocytosis of Escherichia coli and of Staphylococcus aureus by THP-1 cells and RAW264.7 cells was inhibited by resveratrol in a dose-dependent manner regardless of stimulation with FSL-1. The NF-kappaB activity in HEK293 cells stably expressing TLR2 was also inhibited by resveratrol after stimulation with FSL-1. Resveratrol also inhibited both the translocation of p65 of NF-kappaB into nuclei in the transfectant and tumor necrosis factor alpha production by THP-1 cells or RAW264.7 cells. It has recently been reported that TLR-mediated signaling pathways lead to the upregulation of mRNAs of phagocytic receptors, including scavenger receptors and C-type lectin receptors. This study also demonstrated that FSL-1 induced the upregulation of mRNAs of phagocytic receptors such as macrophage scavenger receptor-1, CD36, DC-SIGN, and Dectin-1 and that the FSL-1-induced upregulation of their mRNAs was inhibited by resveratrol. In addition, it was found that the expression of DC-SIGN in HEK293 cells stably expressing DC-SIGN was reduced by resveratrol and that the phagocytic activity was significantly inhibited by resveratrol. Thus, this study suggests that resveratrol inhibited bacterial phagocytosis by macrophages by downregulating the expression of phagocytic receptors and NF-kappaB activity.

Subcapsular sinus macrophages in lymph nodes clear lymph-borne viruses and present them to antiviral B cells

Lymph nodes prevent the systemic dissemination of pathogens such as viruses that infect peripheral tissues after penetrating the body's surface barriers. They are also the staging ground of adaptive immune responses to pathogen-derived antigens. It is unclear how virus particles are cleared from afferent lymph and presented to cognate B cells to induce antibody responses. Here we identify a population of CD11b+CD169+MHCII+ macrophages on the floor of the subcapsular sinus (SCS) and in the medulla of lymph nodes that capture viral particles within minutes after subcutaneous injection. Macrophages in the SCS translocated surface-bound viral particles across the SCS floor and presented them to migrating B cells in the underlying follicles. Selective depletion of these macrophages compromised local viral retention, exacerbated viraemia of the host, and impaired local B-cell activation. These findings indicate that CD169+ macrophages have a dual physiological function. They act as innate 'flypaper' by preventing the systemic spread of lymph-borne pathogens and as critical gatekeepers at the lymph-tissue interface that facilitate the recognition of particulate antigens by B cells and initiate humoral immune responses.

Age-related macular degeneration and the immune response: implications for therapy

PURPOSE

To review the available information concerning the immune mediation of age-related macular degeneration (AMD) and to speculate on proposed mechanisms and immunotherapy.

DESIGN

Interpretative essay.

METHODS

Literature review and interpretation.

RESULTS

An ever-growing body of evidence is gathering concerning the role of the immune system in AMD. Evidence to date suggests that the underlying mechanism leading to AMD is the decline of the ocular downregulatory immune environment. The subsequent activation of the immune system would lead to T-cell sensitization. When combined with local antiangiogenic therapy, several existing immunotherapies may be used to downregulate the immune response, potentially leading to a more efficient inhibition of choroidal neovascularization.

CONCLUSIONS

The loss of the downregulatory immune environment is central to the development of AMD, permitting activation of the immune system. If so, immunotherapy could positively alter the course of the disease.

Langerhans Cell Receptors

Langerhans cells (LC) are a subtype of dendritic cells, which reside in the epidermis. LCs are antigen-presenting cells that originate in bone marrow and enter the epidermis through blood vessels. LCs exhibit a variety of antigen receptors that are able to respond to a wide range of antigens. Within the last two decades, these receptors have been the subject of considerable research. This article focuses on the rapidly growing body of knowledge with respect to the functions of LC receptors.

Innate and adaptive immune response to apoptotic cells

The immune system is constantly exposed to dying cells, most of which arise during central tolerance and from effete circulating immune cells. Under homeostatic conditions, phagocytes (predominantly macrophages and dendritic cells) belonging to the innate immune system, rapidly ingest cells and their debris. Apoptotic cell removal requires recognition of altered self on the apoptotic membrane, a process which is facilitated by natural antibodies and serum opsonins. Recognition, may be site and context specific. Uptake and ingestion of apoptotic cells promotes an immunosuppressive environment that avoids inflammatory responses to self-antigens. However, it does not preclude a T cell response and it is likely that constant exposure to self-antigen, particularly by immature dendritic cells, leads to T cell tolerance. Tolerance occurs by several different mechanisms including anergy and deletion (for CD8+T cells) and induction of T regulatory cells (for CD4+T cells). Failed apoptotic cell clearance promotes immune responses to self-antigens, especially when the cellular contents are leaked from the cell (necrosis). Inflammatory responses may be induced by nucleic acid stimulation of Toll like receptors and other immune sensors, specific intracellular proteins and non-protein (uric acid) stimulation of inflammasomes.

Signaling pathways downstream of pattern-recognition receptors and their cross talk

Pattern-recognition receptors (PRRs) initiate innate immunity through pathogen recognition. Serum PRRs opsonize pathogens for enhanced phagocytic clearance. Toll-like receptors (TLRs) initiate common NF-kappaB/AP-1 and distinct IRF3/7 pathways to coordinate innate immunity and to initiate adaptive immunity against diverse pathogens. Cytoplasmic caspase-recruiting domain (CARD) helicases, such as RIG-I/MDA5, mediate antiviral immunity by inducing the production of type I interferons via the adaptor IPS-1, whereas nucleotide-binding oligomerization domain (NOD)-like receptors mediate mainly antibacterial immunity by activating NF-kappaB or inflammasomes. Dectin-1 is important for antifungal immunity, promoting phagocytosis and activating NF-kappaB. Potentially harmful TLR signaling pathways can be negatively regulated by negative feedback mechanisms and also by anti-inflammatory factors such as TGFbeta, interleukin (IL)-10, and steroids. Many combinations of TLR-TLR and TLR-NOD modulate inflammatory responses. TLRs and NALP3 interplay to produce mature IL-1beta. Thus signaling pathways downstream of PRRs and their cross talk control immune responses in effective manners.