Nontransformed, GM-CSF-dependent macrophage lines are a unique model to study tissue macrophage functions.

Macrophages are diverse cell types in the first line of antimicrobial defense. Only a limited number of primary mouse models exist to study their function. Bone marrow-derived, macrophage-CSF-induced cells with a limited life span are the most common source.

Bacterial sensing, cell signaling, and modulation of the immune response during sepsis.

Since the definition of systemic inflammatory response syndrome/sepsis was originally proposed, a large amount of new information has been generated showing a much more complex scenario of inflammatory and counterinflammatory responses during sepsis. Moreover, some fundamental mechanisms of sensing and destroying invading microorganisms have been uncovered, which include the discovery of TLR4 as the lipopolysaccharide (LPS) gene, implications of innate immune cells as drivers of the adaptive response to infection, and the modulation of multiple accessory molecules that stimulate or inhibit monocyte/macrophage and lymphocyte interactions. The complexity of the infection/injury-induced immune response could be better appreciated with the application of genomics and proteomics studies, and LPS was a useful tool in many of these studies.

TLR9-dependent and independent pathways drive activation of the immune system by Propionibacterium acnes.

Propionibacterium acnes is usually a relatively harmless commensal. However, under certain, poorly understood conditions it is implicated in the etiology of specific inflammatory diseases. In mice, P.

Absence of TRIF signaling in lipopolysaccharide-stimulated murine mast cells.

In macrophages, two signaling pathways, dependent on MyD88 or TIR domain-containing adaptor-inducing IFN-β (TRIF) signaling, emanate from the LPS receptor TLR4/MD-2. In this study, we show that in murine bone marrow-derived mast cells (BMMCs), only the MyD88-dependent pathway is activated by LPS. The TRIF signaling branch leading both to NF-κB activation and enhanced proinflammatory cytokine production, as well as to IRF3 activation and subsequent IFN-β production, is absent in LPS-stimulated BMMCs.

Crucial role for human Toll-like receptor 4 in the development of contact allergy to nickel.

Allergies to nickel (Ni(2+)) are the most frequent cause of contact hypersensitivity (CHS) in industrialized countries. The efficient development of CHS requires both a T lymphocyte-specific signal and a proinflammatory signal. Here we show that Ni(2+) triggered an inflammatory response by directly activating human Toll-like receptor 4 (TLR4).

Innate, antigen-independent role for T cells in the activation of the immune system by Propionibacterium acnes.

Propionibacterium acnes is a human commensal but also an opportunistic pathogen. In mice, P. acnes exerts strong immunomodulatory activities, including formation of intrahepatic granulomas and induction of LPS hypersensitivity.

Tumour Biology: tumour-associated inflammation versus antitumor immunity.

The latest research results suggest that tumour-infiltrating leukocytes and the intra-tumoural cytokine environment play a central role in both the genesis and development of cancer. Over a hundred years ago, Virchow pointed out that numerous immune cells occur in the vicinity of practically all malignant tumours and that the structure of tumour tissue closely resembles the inflamed region of a non-healing wound. With the aid of the latest molecular and cell-biological methods, we are not only able today to closely characterise tumour cells and their immediate vicinity but also the other cell types present in tumour tissue, such as infiltrating immune cells, endothelial cells, connective tissue cells and others, both in terms of phenotype and function.

Enhanced B-cell activation mediated by TLR4 and BCR crosstalk.

Despite the important role of B lymphocytes as a bridge between the innate and the adaptive immune system, little is known regarding lipopolysaccharide (LPS) recognition, activation of signalling networks or conceivable cooperation between LPS and the B-cell antigen receptor (BCR). Here, we show that primary B cells can efficiently discriminate between different LPS chemotypes, responding with at least 100-fold higher sensitivity to rough-form LPS compared with smooth-form LPS. Using genetically modified mice, we demonstrate that B lymphocytes recognize all LPS chemotypes via Toll-like receptor 4 (TLR4).

Toll-like receptor and IL-12 signaling control susceptibility to contact hypersensitivity.

Allergic contact hypersensitivity (CHS) is a T cell-mediated inflammatory skin disease. Interleukin (IL)-12 is considered to be important in the generation of the allergen-specific T cell response. Loss of IL-12 function in IL-12Rbeta2-deficient mice, however, did not ameliorate the allergic immune response, suggesting alternate IL-12-independent pathways in the induction of CHS.

Lipopolysaccharide sensing an important factor in the innate immune response to Gram-negative bacterial infections: benefits and hazards of LPS hypersensitivity.

In this review, we summarize our investigations concerning the differential importance of CD14 and LBP in toll-like receptor 4 (TLR4)/myeloid differentiation protein-2 (MD-2)-mediated signaling by smooth and rough-form lipopolysaccharide (LPS) chemotypes and include the results obtained in studies with murine and human TLR4-transgenic mice. Furthermore, we present more recent data on the mechanisms involved in the induction of LPS hypersensitivity by bacterial and viral infections and on the reactivity of the hypersensitive host to non-LPS microbial ligands and endogenous mediators. Finally, the effects of pre-existing hypersensitivity on the course and outcome of a super-infection with Salmonella typhimurium or Listeria monocytogenes are summarized.

Stage of primary infection with lymphocytic choriomeningitis virus determines predisposition or resistance of mice to secondary bacterial infections.

We investigated the effect of a primary non-lethal infection with lymphocytic choriomeningitis virus (LCMV) on the course and outcome of a secondary infection with the Gram-negative Salmonella enterica serovar Typhimurium or the Gram-positive Listeria monocytogenes in mice. We found that at each stage of the viral infection the susceptibility of mice to bacterial super-infections changes dramatically and depends also on whether the secondary infection is a Gram-positive or Gram-negative one. The study shows that the outcome of the secondary infection is determined by a delicate balance between the overproduction of and the hypersensitivity to inflammatory cytokines (TNF-alpha and IFN-gamma), as well as by the changes in blood leukocytes occurring in mice in the course of viral infection.

Stimulation of mast cells via FcvarepsilonR1 and TLR2: the type of ligand determines the outcome.

Little is known about the interplay between pathophysiological processes of allergy and infection, particularly with respect to mast cell (MC)-mediated responses. The presence and recognition of pathogen-associated molecular patterns (PAMPs) might have broad impact on the development and severity of diseases. In this study, we assessed the influence of toll-like receptor 2 (TLR 2)-dependent synthetic analogs of bacterial lipopeptides (LPs), Pam(3)CSK(4) and MALP-2, on Ag (DNP-HSA)-triggered responses in bone marrow-derived MCs (BMMCs).

R-form LPS, the master key to the activation ofTLR4/MD-2-positive cells.

Lipopolysaccharide (endotoxin, LPS) is a major recognition marker for the detection of gram-negative bacteria by the host and a powerful initiator of the inflammatory response to infection. Using S- and R-form LPS from wild-type and R-mutants of Salmonella and E. coli, we show that R-form LPS readily activates mouse cells expressing the signaling receptor Toll-like receptor 4/myeloid differentiation protein 2 (TLR4/MD-2), while the S-form requires further the help of the LPS-binding proteins CD14 and LBP, which limits its activating capacity.

Lethal effect and apoptotic DNA fragmentation in response of D-GalN-treated mice to bacterial LPS can be suppressed by pre-exposure to minute amount of bacterial LPS: dual role of TNF receptor 1.

Aim: To investigate whether induction of tolerance of mice to lipopolysaccharide (LPS) was able to inhibit apoptotic reaction in terms of characteristic DNA fragmentation and protect mice from lethal effect.

Methods: Experimental groups of mice were pretreated with non-lethal amount of LPS (0.05 microg).

CD14 is required for MyD88-independent LPS signaling.

The recessive mutation 'Heedless' (hdl) was detected in third-generation N-ethyl-N-nitrosourea-mutated mice that showed defective responses to microbial inducers. Macrophages from Heedless homozygotes signaled by the MyD88-dependent pathway in response to rough lipopolysaccharide (LPS) and lipid A, but not in response to smooth LPS. In addition, the Heedless mutation prevented TRAM-TRIF-dependent signaling in response to all LPS chemotypes.

Requirement for TLR9 in the immunomodulatory activity of Propionibacterium acnes.

Propionibacterium acnes (formerly Corynebacterium parvum) is part of the human flora and, as such, is associated with several human pathologies. It possesses strong immunomodulatory activities, which makes this bacterium interesting for prophylactic and therapeutic vaccination. The bacterial component(s) and the host receptor(s) involved in the induction of these activities are poorly understood.

Chemokine gene expression in toll-like receptor-competent and -deficient mice infected with Leishmania major.

We studied the expression of a subset of chemokines, including RANTES/CCL5, MIP-1alpha/CCL3, IP-10/CXCL10, and MCP-1/CCL2, in Toll-like receptor (TLR)-competent and -deficient mice after infection with Leishmania major. Chemokine expression at the site of infection (the footpad), in the draining lymph nodes and in the spleens of infected animals was determined by using two different methods of analysis. The results indicate that L.

Toll-like receptor 4 contributes to efficient control of infection with the protozoan parasite Leishmania major.

The essential role of Toll-like receptors (TLR) in innate immune responses to bacterial pathogens is increasingly recognized, but very little is known about the role of TLRs in host defense against infections with eukaryotic pathogens. For the present study, we investigated whether TLRs contribute to the innate and acquired immune response to infection with the intracellular protozoan parasite Leishmania major. Our results show that TLR4 contributes to the control of parasite growth in both phases of the immune response.

Role of interferons in LPS hypersensitivity.

The innate immune response to Gram-negative bacteria depends mainly on the ability of the host to respond to the LPS component. Consequently, the state of LPS sensitivity at the time of infection and the numbers of invading bacteria (i.e.

Differential contribution of Toll-like receptors 4 and 2 to the cytokine response to Salmonella enterica serovar Typhimurium and Staphylococcus aureus in mice.

The contribution of murine Toll-like receptors 2 and 4 (TLR2 and -4, respectively) to cytokine induction by heat-killed bacteria was analyzed in vitro and in vivo. Gram-negative bacteria induced cytokines primarily via TLR4; the contribution of TLR2 was only minor. Neither TLR4 nor, surprisingly, TLR2 was required in the MyD88-dependent response to Staphylococcus aureus.

TNF revisited: TNF-independent antitumor activity in sera of mice sensitized with Propionibacterium acnes and challenged with lipopolysaccharide.

Sera of mice sensitized with bacteria and subsequently challenged with lipopolysaccharide promote hemorrhagic necrosis of tumors in vivo and display cytotoxic activity against tumor cells in vitro, which has been attributed to the induction of tumor necrosis factor (TNF). Here, we describe the induction of a previously unrecognized antitumor activity in such sera, which is distinct from TNF but displays tumor-specific cytocidal activity in vitro as well as potent tumor-regressing activity in vivo. Biochemical analysis of this activity yielded a molecular mass of approximately 150 kDa, closely resembling a novel tumoricidal factor of murine macrophages (Mphi) termed MTC 170 (Mphi tumor cytotoxin, approximate molecular mass 170 kDa), which we have previously proposed to constitute a major effector pathway for the destruction of tumor cells by activated Mphi.

Toll-like receptor 2- and 6-mediated stimulation by macrophage-activating lipopeptide 2 induces lipopolysaccharide (LPS) cross tolerance in mice, which results in protection from tumor necrosis factor alpha but in only partial protection from lethal LPS doses.

Patients or experimental animals previously exposed to lipopolysaccharide (LPS) become tolerant to further LPS challenge. We investigated the potential of the macrophage-activating lipopeptide 2 (MALP-2) to induce in vivo cross tolerance to tumor necrosis factor alpha (TNF-alpha) and LPS. MALP-2-induced tolerance could be of practical interest, as MALP-2 proved much less pyrogenic in rabbits than LPS.

A striking correlation between lethal activity and apoptotic DNA fragmentation of liver in response of D-galactosamine-sensitized mice to a non-lethal amount of lipopolysaccharide.

Aim: To observe whether challenge of bacterial lipopolysaccharide (LPS) with D-galactosamine (D-GalN) in mice will result in apoptotic characteristic of vital organs.

Methods: The experimental group of mice was challenged directly with bacterial LPS (0.05 microg) in the presence of D-GalN (20 mg), and the control group of mice was challenged either with bacterial LPS or with D-GalN alone.

Toll-like receptor 4 expression levels determine the degree of LPS-susceptibility in mice.

C57BL/10ScCr (Cr) mice carry a deletion of the Toll-like receptor 4 (tlr4) gene (i.e. they are tlr4(0/0)) and are thus refractory to LPS effects.

Antitumor effect of the human immunodeficiency virus protease inhibitor ritonavir: induction of tumor-cell apoptosis associated with perturbation of proteasomal proteolysis.

Ritonavir is an HIV protease inhibitor used in the therapy of HIV infection. Ritonavir has also been shown to inhibit the chymotrypsin-like activity of isolated 20S proteasomes. Here, we demonstrate that ritonavir, like classical proteasome inhibitors, has antitumoral activities.