Autocrine and exocrine regulation of interleukin-10 production in THP-1 cells stimulated with Borrelia burgdorferi lipoproteins

Decades Long Involvement of THP-1 Cells as a Model for Macrophage Research: A Comprehensive Review

Over the years, researchers have endeavored to identify dependable and reproducible in vitro models for examining macrophage behavior under controlled conditions. The THP-1 cell line has become a significant and widely employed tool in macrophage research within these models. Originating from the peripheral blood of individuals with acute monocytic leukemia, this human monocytic cell line can undergo transformation into macrophage-like cells, closely mirroring primary human macrophages when exposed to stimulants. Macrophages play a vital role in the innate immune system, actively regulating inflammation, responding to infections, and maintaining tissue homeostasis. A comprehensive understanding of macrophage biology and function is crucial for gaining insights into immunological responses, tissue healing, and the pathogenesis of diseases such as viral infections, autoimmune disorders, and neoplastic conditions. This review aims to thoroughly evaluate and emphasize the extensive history of THP-1 cells as a model for macrophage research. Additionally, it will delve into the significance of THP-1 cells in advancing our comprehension of macrophage biology and their invaluable contributions to diverse scientific domains.

Two transcription factors PU.1a and PU.1b have different functions in the immune system of teleost ayu

Transcription factor PU.1 is a regulator of macrophage function, however, the specific function of PU.1 in teleost monocytes/macrophages (MO/MФ) remains unknown. We determined the cDNA sequence of two PU.1 genes from ayu (Plecoglossus altivelis; PaPU.1a and PaPU.1b). Sequence comparisons showed that PaPU.1 were most closely related to the PU.1 of rainbow smelt (Osmerus mordax). The PU.1 transcripts were mainly expressed in the spleen, and their expression was altered in various tissues upon infection with Vibrio anguillarum. PaPU.1a and PaPU.1b proteins were upregulated in MO/MФ, after infection. RNA interference was employed to knockdown PaPU.1a and PaPU.1b to investigate their function in MO/MФ. The expression of inflammatory cytokines was regulated by PaPU.1a, but not PaPU.1b, in ayu MO/MФ upon V. anguillarum infection. Both PaPU.1a and PaPU.1b knockdown lowered the phagocytic activity of MO/MФ. Furthermore, PaPU.1b knockdown attenuated MO/MФ bacterial killing capability. Our results indicate that two PaPU.1 genes differentially modulate the immune response in ayu MO/MФ against bacterial infection.

Spirochetal Lipoproteins and Immune Evasion

Spirochetes are a major threat to public health. However, the exact pathogenesis of spirochetal diseases remains unclear. Spirochetes express lipoproteins that often determine the cross talk between the host and spirochetes. Lipoproteins are pro-inflammatory, modulatory of immune responses, and enable the spirochetes to evade the immune system. In this article, we review the modulatory effects of spirochetal lipoproteins related to immune evasion. Understanding lipoprotein-induced immunomodulation will aid in elucidating innate pathogenesis processes and subsequent adaptive mechanisms potentially relevant to spirochetal disease vaccine development and treatment.

Rv0774c, an iron stress inducible, extracellular esterase is involved in immune-suppression associated with altered cytokine and TLR2 expression

Tuberculosis, one of the leading cause of death from infectious diseases, is caused by Mycobacterium tuberculosis. The genome of M. tuberculosis has been sequenced and nearly 40% of the whole genome sequence was categorized as hypothetical. Rv0774c was annotated as membrane exported hypothetical protein in TB database. In silico analysis revealed that Rv0774c is a paralog of PE-PGRS multi gene family with 100 aa N-terminal domain similar to PE domain of PE-PGRS proteins. Its C-terminal domain is quite different from PGRS domain, having characteristic lipase signature GXSXG & HG and catalytic residues predicted for lipolytic activity. Therefore, DNA coding for Rv0774c (303 aa), its N-terminal (1-100 aa) and C- terminal domain (100-303 aa) were separately cloned from M. tuberculosis and were over expressed in E. coli. Rv0774c gene and its C-terminal lipolytic domain preferably hydrolyzed short chain esters. Though no enzyme activity was observed in N-terminus PE like domain, it was demonstrated to enhance the thermostability of full length Rv0774c. Tetrahydrolipstatin inhibited the enzyme activity and predicted catalytic residues (Ser-185, Asp-255 and His-281) were confirmed by site directed mutagenesis. Rv0774c was secreted out in culture media by M. tuberculosis and was up-regulated in iron limiting conditions. Treatment of THP-1 cells with rRv0774c resulted in a decline in the LPS induced production of NO and expression of iNOS. rRv0774c treated THP-1 cells also showed an enhanced expression of IL-10 and TLR2. On contrary, it suppressed the LPS induced production of IL-12, chemokines MCP-1 and IL-8. Rv0774c inhibited the LPS induced phosphorylation of p38. These observations suggested that Rv0774c could modulate the pro-inflammatory immune response to support intracellular survival of the mycobacterium.

Differentiated THP-1 Cells Exposed to Pathogenic and Nonpathogenic Borrelia Species Demonstrate Minimal Differences in Production of Four Inflammatory Cytokines

Tick-borne borreliae include Lyme disease and relapsing fever agents, and they are transmitted primarily by ixodid (hard) and argasid (soft) tick vectors, respectively. Tick-host interactions during feeding are complex, with host immune responses influenced by biological differences in tick feeding and individual differences within and between host species. One of the first encounters for spirochetes entering vertebrate host skin is with local antigen-presenting cells, regardless of whether the tick-associated Borrelia sp. is pathogenic. In this study, we performed a basic comparison of cytokine responses in THP-1-derived macrophages after exposure to selected borreliae, including a nonpathogen. By using THP-1 cells, differentiated to macrophages, we eliminated variations in host response and reduced the system to an in vitro model to evaluate the extent to which the Borrelia spp. influence cytokine production. Differentiated THP-1 cells were exposed to four Borrelia spp., Borrelia hermsii (DAH), Borrelia burgdorferi (B31), B. burgdorferi (NC-2), or Borrelia lonestari (LS-1), or lipopolysaccharides (LPS) (activated) or media (no treatment) controls. Intracellular and secreted interferon (IFN)-γ, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α were measured using flow cytometric and Luminex-based assays, respectively, at 6, 24, and 48 h postexposure time points. Using a general linear model ANOVA for each cytokine, treatment (all Borrelia spp. and LPS compared to no treatment) had a significant effect on secreted TNF-α only. Time point had a significant effect on intracellular IFN-γ, TNF-α and IL-6. However, we did not see significant differences in selected cytokines among Borrelia spp.

TREATMENTS

Thus, in this model, we were unable to distinguish pathogenic from nonpathogenic borreliae using the limited array of selected cytokines. While unique immune profiles may be detectable in an in vitro model and may reveal predictors for pathogenicity in borreliae of unknown pathogenicity, a larger panel of cytokines would be desirable to test.

Immunomodulatory effects of tick saliva on dermal cells exposed to Borrelia burgdorferi, the agent of Lyme disease

BACKGROUND

The prolonged feeding process of ixodid ticks, in combination with bacterial transmission, should lead to a robust inflammatory response at the blood-feeding site. Yet, factors present in tick saliva may down-regulate such responses, which may be beneficial to spirochete transmission. The primary goal of this study was to test the hypothesis that tick saliva, in the context of Borrelia burgdorferi, can have widespread effects on the production of immune mediators in skin.

METHODS

A cross-section of tick feeding on skin was examined histologically. Human THP-1 cells stimulated with B. burgdorferi and grown in the presence or absence of tick saliva were examined by human DNA microarray, cytokine bead array, sandwich ELISA, and qRT-PCR. Similar experiments were also conducted using dermal fibroblasts.

RESULTS

Tick feeding on skin showed dermal infiltration of histiocytes and granulocytes at the bite location. Changes in monocytic transcript levels during co-culture with B. burgdorferi and saliva indicated that tick saliva had a suppressive effect on the expression of certain pro-inflammatory mediators, such as IL-8 (CXCL8) and TLR2, but had a stimulatory effect on specific molecules such as the Interleukin 10 receptor, alpha subunit (IL-10RA), a known mediator of the immunosuppressive signal of IL-10. Stimulated cell culture supernatants were analyzed via antigen-capture ELISA and cytokine bead array for inflammatory mediator production. Treatment of monocytes with saliva significantly reduced the expression of several key mediators including IL-6, IL-8 and TNF-alpha. Tick saliva had an opposite effect on dermal fibroblasts. Rather than inhibiting, saliva enhanced production of pro-inflammatory mediators, including IL-8 and IL-6 from these sentinel skin cells.

CONCLUSIONS

The effects of ixodid tick saliva on resident skin cells is cell type-dependent. The response to both tick and pathogen at the site of feeding favors pathogen transmission, but may not be wholly suppressed by tick saliva.

Increased expression of Fas receptor and Fas ligand in the culture of the peripheral blood mononuclear cells stimulated with Borrelia burgdorferi sensu lato

Apoptosis of the lymphocytes plays an essential role in the regulation of inflammatory/immune responses and its abnormalities may contribute to a chronic infection, persistent inflammation and autoimmunity. Its role in the pathogenesis of the late Lyme borreliosis manifestations has not been studied so far. We have measured Th lymphocyte apoptosis rate, membrane expression of pro-apoptotic Fas receptor, and supernatant concentrations of selected soluble pro- and anti-apoptotic mediators in cultures of peripheral blood mononuclear cells from 16 patients with disseminated Lyme borreliosis (6 with osteoarticular symptoms, 7 with neuroborreliosis and 3 with acrodermatitis chronica atrophicans) and 8 healthy controls. The cultures stimulated for 48h with live Borrelia burgdorferi sensu stricto, B. garinii or B. afzelii spirochetes. Fraction of the apoptotic Th (CD3+CD4+) lymphocytes and expression of Fas in this cell population was measured cytometrically and concentrations of soluble Fas, soluble Fas ligand, IL-10, IL-12 and TGF-β in culture supernatant with ELISA assays. The expression of IL-10, soluble and membrane Fas and soluble Fas ligand was increased under stimulation and higher in the presence of B. burgdorferi sensu stricto than the other species. Apoptosis rate was not affected. There was no difference between Lyme borreliosis patients and controls. IL-10 concentration correlated negatively with the membrane Fas expression and apoptosis under stimulation with B. afzelii and B. garinii. Expression of Fas/FasL system is up-regulated under stimulation with B. burgdorferi, but without corresponding increase in lymphocyte apoptosis. Variable responses observed with different B. burgdorferi species may reflect differences in the pathogenesis of the infection in vivo.

Development of an experimental model for assessing the effects of cigarette smoke and virus infections on inflammatory responses to bacterial antigens

Interactions among major risk factors associated with bacterial infections were assessed in a model system using surrogates for virus infection; IFN-g, and exposure to cigarette smoke; cigarette smoke extract (CSE), nicotine and cotinine. Cytokine responses elicited by LPS from THP-1 cells in the presence of these components, or combinations of components, were assessed by multiplex bead assay, i.e. IL-1β, IL-6, IL-8, IL-10, TNF-α and IFN-γ. IFN-γ-priming significantly increased pro-inflammatory cytokines induced by LPS. CSE suppressed production of pro-inflammatory cytokines IL-1β, TNF-α and IFN-γ, but enhanced production of IL-8. Nicotine and cotinine suppressed all cytokine responses. In combination, IFN-γ masked the inhibitory effects of CSE. In relation to the objectives of the study, we concluded that (a) IFN-γ at biologically relevant concentrations significantly enhanced pro-inflammatory responses; (b) CSE, nicotine and cotinine dysregulated the inflammatory response and that the effects of CSE were different from those of the individual components, nicotine and cotinine; (c) when both IFN-γ and CSE were present, IFN-γ masked the effect of CSE. There is a need for clinical investigations on the increase in IL-8 responses in relation to exposure to cigarette smoke and increased pro-inflammatory responses in relation to recent viral infection.

The Cross-Talk between Spirochetal Lipoproteins and Immunity

Spirochetal diseases such as syphilis, Lyme disease, and leptospirosis are major threats to public health. However, the immunopathogenesis of these diseases has not been fully elucidated. Spirochetes interact with the host through various structural components such as lipopolysaccharides (LPS), surface lipoproteins, and glycolipids. Although spirochetal antigens such as LPS and glycolipids may contribute to the inflammatory response during spirochetal infections, spirochetes such as Treponema pallidum and Borrelia burgdorferi lack LPS. Lipoproteins are most abundant proteins that are expressed in all spirochetes and often determine how spirochetes interact with their environment. Lipoproteins are pro-inflammatory, may regulate responses from both innate and adaptive immunity and enable the spirochetes to adhere to the host or the tick midgut or to evade the immune system. However, most of the spirochetal lipoproteins have unknown function. Herein, the immunomodulatory effects of spirochetal lipoproteins are reviewed and are grouped into two main categories: effects related to immune evasion and effects related to immune activation. Understanding lipoprotein-induced immunomodulation will aid in elucidating innate immunopathogenesis processes and subsequent adaptive mechanisms potentially relevant to spirochetal disease vaccine development and to inflammatory events associated with spirochetal diseases.

Borrelia burgdorferi elicited-IL-10 suppresses the production of inflammatory mediators, phagocytosis, and expression of co-stimulatory receptors by murine macrophages and/or dendritic cells

Borrelia burgdorferi (Bb) is a tick-borne spirochete that is the causative agent for Lyme disease. Our previous studies indicate that virulent Bb can potently enhance IL-10 production by macrophages (MØs) and that blocking IL-10 production significantly enhances bacterial clearance. We hypothesize that skin-associated APC types, such as MØs and dendritic cells (DCs) are potent producers of IL-10 in response to Bb, which may act in autocrine fashion to suppress APC responses critical for efficient Bb clearance. Our goal is to delineate which APC immune functions are dysregulated by Bb-elicited IL-10 using a murine model of Lyme disease. Our in vitro studies indicated that both APCs rapidly produce IL-10 upon exposure to Bb, that these levels inversely correlate with the production of many Lyme-relevant proinflammatory cytokines and chemokines, and that APCs derived from IL-10(-/-) mice produced greater amounts of these proinflammatory mediators than wild-type APCs. Phagocytosis assays determined that Bb-elicited IL-10 levels can diminish Bb uptake and trafficking by MØs, suppresses ROS production, but does not affect NO production; Bb-elicited IL-10 had little effect on phagocytosis, ROS, and NO production by DCs. In general, Bb exposure caused little-to-no upregulation of several critical surface co-stimulatory markers by MØs and DCs, however eliminating Bb-elicited IL-10 allowed a significant upregulation in many of these co-stimulatory receptors. These data indicate that IL-10 elicited from Bb-stimulated MØs and DCs results in decreased production of proinflammatory mediators and co-stimulatory molecules, and suppress phagocytosis-associated events that are important for mediating both innate and adaptive immune responses by APCs.

Different patterns of expression and of IL-10 modulation of inflammatory mediators from macrophages of Lyme disease-resistant and -susceptible mice

C57BL/6J (C57) mice develop mild arthritis (Lyme disease-resistant) whereas C3H/HeN (C3H) mice develop severe arthritis (Lyme disease-susceptible) after infection with the spirochete Borrelia burgdorferi. We hypothesized that susceptibility and resistance to Lyme disease, as modeled in mice, is associated with early induction and regulation of inflammatory mediators by innate immune cells after their exposure to live B. burgdorferi spirochetes. Here, we employed multiplex ELISA and qRT-PCR to investigate quantitative differences in the levels of cytokines and chemokines produced by bone marrow-derived macrophages from C57 and C3H mice after these cells were exposed ex vivo to live spirochetes or spirochetal lipoprotein. Upon stimulation, the production of both cytokines and chemokines was up-regulated in macrophages from both mouse strains. Interestingly, however, our results uncovered two distinct patterns of spirochete- and lipoprotein-inducible inflammatory mediators displayed by mouse macrophages, such that the magnitude of the chemokine up-regulation was larger in C57 cells than it was in C3H cells, for most chemokines. Conversely, cytokine up-regulation was more intense in C3H cells. Gene transcript analyses showed that the displayed patterns of inflammatory mediators were associated with a TLR2/TLR1 transcript imbalance: C3H macrophages expressed higher TLR2 transcript levels as compared to those expressed by C57 macrophages. Exogenous IL-10 dampened production of inflammatory mediators, especially those elicited by lipoprotein stimulation. Neutralization of endogenously produced IL-10 increased production of inflammatory mediators, notably by macrophages of C57 mice, which also displayed more IL-10 than C3H macrophages. The distinct patterns of pro-inflammatory mediator production, along with TLR2/TLR1 expression, and regulation in macrophages from Lyme disease-resistant and -susceptible mice suggests itself as a blueprint to further investigate differential pathogenesis of Lyme disease.

Systematic review of membrane components of gram-positive bacteria responsible as pyrogens for inducing human monocyte/macrophage cytokine release

Fifty years after the elucidation of lipopolysaccharides (LPS, endotoxin) as the principal structure of Gram-negative bacteria activating the human immune system, its Gram-positive counterpart is still under debate. Pyrogen tests based on the human monocyte activation have been validated for LPS detection as an alternative to the rabbit test and, increasingly, the limulus amebocyte lysate test. For full replacement, international validations with non-endotoxin pyrogens are in preparation. Following evidence-based medicine approaches, a systematic review of existing evidence as to the structural nature of the Gram-positive pyrogen was undertaken. For the three major constituents suggested, i.e., peptidoglycan, lipoteichoic acids (LTA), and bacterial lipoproteins (LP), the questions to be answered and a search strategy for relevant literature was developed, starting in MedLine. The evaluation was based on the Koch–Dale criteria for a mediator of an effect. A total of 380 articles for peptidoglycan, 391 for LP, and 285 for LTA were retrieved of which 12, 8, and 24, respectively, fulfilled inclusion criteria. The compiled data suggest that for peptidoglycan two Koch–Dale criteria are fulfilled, four for LTA, and two for bacterial LP. In conclusion, based on the best currently available evidence, LTA is the only substance that fulfills all criteria. LTA has been isolated from a large number of bacteria, results in cytokine release patterns inducible also with synthetic LTA. Reduction in bacterial cytokine induction with an inhibitor for LTA was shown. However, this systematic review cannot exclude the possibility that other stimulatory compounds complement or substitute for LTA in being the counterpart to LPS in some Gram-positive bacteria.

Transcription profiles of LPS-stimulated THP-1 monocytes and macrophages: a tool to study inflammation modulating effects of food-derived compounds

An assay was developed to study inflammation-related immune responses of food compounds on monocytes and macrophages derived from THP-1 cell line. First strategy focused on the effects after stimulation with either lipopolysaccharide (LPS) or Concanavalin A (ConA). Gene expression kinetics of inflammation-related cytokines (IL-1β, IL-6, IL-8, IL-10 and TNF-α), inflammation-related enzymes (iNOS and COX-2), and transcription factors (NF-κB, AP-1 and SP-1) were analyzed using RT-PCR. Time dependent cytokine secretion was investigated to study the inflammation-related responses at protein level. LPS stimulation induced inflammation-related cytokine, COX-2 and NF-κB genes of THP-1 monocytes and THP-1 macrophages with the maximum up-regulation at 3 and 6 h, respectively. These time points, were subsequently selected to investigate inflammation modulating activity of three well known immuno-modulating food-derived compounds; quercetin, citrus pectin and barley glucan. Co-stimulation of LPS with either quercetin, citrus pectin, or barley glucan in THP-1 monocytes and macrophages showed different immuno-modulatory activity of these compounds. Therefore, we propose that simultaneously exposing THP-1 cells to LPS and food compounds, combined with gene expression response analysis are a promising in vitro screening tool to select, in a limited time frame, food compounds for inflammation modulating effects.

Emergence of chronic Lyme arthritis: putting the breaks on CD28 costimulation

Lyme disease is a debilitating infection that is caused upon a bite of Borrelia burgdorferi (Bb)-infected ticks. One of the most prominent clinical manifestations is the development of chronic Lyme arthritis. Months after Bb infection, approximately 60% of untreated Lyme patients experience intermittent arthritic attacks that may last for years. The use of the CD28(-/-) mouse in Bb infection has helped to shed light into the mechanisms that govern this inflammatory process, which seems to be tightly regulated. In this current review, the effect of immunoregulation, as well as CD28 deficiency in the development of chronic Lyme arthritis is discussed.

Resistance to bleomycin-induced lung fibrosis in MMP-8 deficient mice is mediated by interleukin-10

Background

Matrix metalloproteinases (MMPs) may have pro and antifibrotic roles within the lungs, due to its ability to modulate collagen turnover and immune mediators. MMP-8 is a collagenase that also cleaves a number of cytokines and chemokines.

Methodology and Principal Findings

To evaluate its relevance in lung fibrosis, wildtype and Mmp8^−/− mice were treated with either intratracheal bleomycin or saline, and lungs were harvested at different time points. Fibrosis, collagen, collagenases, gelatinases, TGFβ and IL-10 were measured in lung tissue. Mmp8^−/− mice developed less fibrosis than their wildtype counterparts. This was related to an increase in lung inflammatory cells, MMP-9 and IL-10 levels in these mutant animals. In vitro experiments showed that MMP-8 cleaves murine and human IL-10, and tissue from knockout animals showed decreased IL-10 processing. Additionally, lung fibroblasts from these mice were cultured in the presence of bleomycin and collagen, IL-10 and STAT3 activation (downstream signal in response to IL-10) measured by western blotting. In cell cultures, bleomycin increased collagen synthesis only in wildtype mice. Fibroblasts from knockout mice did not show increased collagen synthesis, but increased levels of unprocessed IL-10 and STAT3 phosphorylation. Blockade of IL-10 reverted this phenotype, increasing collagen in cultures.

Conclusions

According to these results, we conclude that the absence of MMP-8 has an antifibrotic effect by increasing IL-10 and propose that this metalloprotease could be a relevant modulator of IL-10 metabolism in vivo.

Microglia are mediators of Borrelia burgdorferi-induced apoptosis in SH-SY5Y neuronal cells

Inflammation has long been implicated as a contributor to pathogenesis in many CNS illnesses, including Lyme neuroborreliosis. Borrelia burgdorferi is the spirochete that causes Lyme disease and it is known to potently induce the production of inflammatory mediators in a variety of cells. In experiments where B. burgdorferi was co-cultured in vitro with primary microglia, we observed robust expression and release of IL-6 and IL-8, CCL2 (MCP-1), CCL3 (MIP-1α), CCL4 (MIP-1β) and CCL5 (RANTES), but we detected no induction of microglial apoptosis. In contrast, SH-SY5Y (SY) neuroblastoma cells co-cultured with B. burgdorferi expressed negligible amounts of inflammatory mediators and also remained resistant to apoptosis. When SY cells were co-cultured with microglia and B. burgdorferi, significant neuronal apoptosis consistently occurred. Confocal microscopy imaging of these cell cultures stained for apoptosis and with cell type-specific markers confirmed that it was predominantly the SY cells that were dying. Microarray analysis demonstrated an intense microglia-mediated inflammatory response to B. burgdorferi including up-regulation in gene transcripts for TLR-2 and NFκβ. Surprisingly, a pathway that exhibited profound changes in regard to inflammatory signaling was triggering receptor expressed on myeloid cells-1 (TREM1). Significant transcript alterations in essential p53 pathway genes also occurred in SY cells cultured in the presence of microglia and B. burgdorferi, which indicated a shift from cell survival to preparation for apoptosis when compared to SY cells cultured in the presence of B. burgdorferi alone. Taken together, these findings indicate that B. burgdorferi is not directly toxic to SY cells; rather, these cells become distressed and die in the inflammatory surroundings generated by microglia through a bystander effect. If, as we hypothesized, neuronal apoptosis is the key pathogenic event in Lyme neuroborreliosis, then targeting microglial responses may be a significant therapeutic approach for the treatment of this form of Lyme disease.

Lyme disease, which is transmitted to humans through the bite of a tick, is currently the most frequently reported vector-borne illness in the northern hemisphere. Borrelia burgdorferi is the bacterium that causes Lyme disease and it is known to readily induce inflammation within a variety of infected tissues. Many of the neurological signs and symptoms that may affect patients with Lyme disease have been associated with B. burgdorferi-induced inflammation in the central nervous system (CNS). In this report we investigated which of the primary cell types residing in the CNS might be functioning to create the inflammatory environment that, in addition to helping clear the pathogen, could simultaneously be harming nearby neurons. We report findings that implicate microglia, a macrophage cell type in the CNS, as the key responders to infection with B. burgdorferi. We also present evidence indicating that this organism is not directly toxic to neurons; rather, a bystander effect is generated whereby the inflammatory surroundings created by microglia in response to B. burgdorferi may themselves be toxic to neuronal cells.

Modelling and simulating interleukin-10 production and regulation by macrophages after stimulation with an immunomodulator of parasitic nematodes

Parasitic nematodes can downregulate the immune response of their hosts through the induction of immunoregulatory cytokines such as interleukin-10 (IL-10). To define the underlying mechanisms, we measured in vitro the production of IL-10 in macrophages in response to cystatin from Acanthocheilonema viteae, an immunomodulatory protein of filarial nematodes, and developed mathematical models of IL-10 regulation. IL-10 expression requires stimulation of the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK) and p38, and we propose that a negative feedback mechanism, acting at the signalling level, is responsible for transient IL-10 production that can be followed by a sustained plateau. Specifically, a model with negative feedback on the ERK pathway via secreted IL-10 accounts for the experimental data. Accordingly, the model predicts sustained phospho-p38 dynamics, whereas ERK activation changes from transient to sustained when the concentration of immunomodulatory protein of Acanthocheilonema viteae increases. We show that IL-10 can regulate its own production in an autocrine fashion, and that ERK and p38 control IL-10 amplitude, duration and steady state. We also show that p38 affects ERK via secreted IL-10 (autocrine crosstalk). These findings demonstrate how convergent signalling pathways may differentially control kinetic properties of the IL-10 signal.

A proinflammatory cytokine interleukin-32beta promotes the production of an anti-inflammatory cytokine interleukin-10

A new proinflammatory cytokine interleukin-32 (IL-32) has six isoforms. Although IL-32 can be detected in sera from patients suffering from Crohn's disease and rheumatoid arthritis, it is unclear which isoforms are involved. To this end, we investigated the functions of the most abundant IL-32beta by generating K562-IL-32beta stable cell lines. This report confirms, using IL-32 small interfering RNA, that IL-32beta induces an anti-inflammatory cytokine IL-10 in K562-IL-32beta cells and U937 promonocytic cells, which express endogenous IL-32beta upon phorbol 12-myristate 13-acetate (PMA) treatment, and monocyte-derived dendritic cells (DC) upon lipopolysaccharide (LPS) treatment. Interleukin-32beta was induced in monocyte-derived macrophages by LPS and in monocyte-derived DC by LPS, poly(I:C), or anti-CD40 antibody, but was not induced by PMA. We showed that IL-32beta expression was increased in a time-dependent manner in monocyte-derived DC upon LPS treatment and peaked at 24 hr. Production of IL-10 was exactly coincident with IL-32beta expression, but IL-1beta and tumour necrosis factor-alpha production peaked at 6 hr after LPS treatment, then steeply declined. Interleukin-12 p40 was induced at 9 hr and gradually increased until 48 hr, at which time IL-32beta and IL-10 were no longer increased. Knock-down of IL-32beta by IL-32 small interfering RNA led to the decrease of IL-10, but the increase of IL-12 in monocyte-derived DC, which means that IL-32beta promotes IL-10 production, but limits IL-12 production. We also showed that IL-10 neutralization increases IL-12, IL-1beta and tumour necrosis factor-alpha production, which implies that IL-10 suppresses such proinflammatory cytokines. Taken together, our results suggest that IL-32beta upregulates the production of an anti-inflammatory cytokine IL-10, and then IL-10 suppresses proinflammatory cytokines.

Review: variability of host-pathogen interaction

The course of every infection is different. The same pathogen can lead to subclinical, mild, severe or lethal infections in individuals. But is this just chance or determined by individual differences--on the side of the host as well as on the side of the pathogen? If so, we might need to consider these variations for treatment decisions. Indeed, we now understand that genetic polymorphisms and health status represent inborn and acquired risk factors. Similarly, pathogens impress with an increasing number of already identified virulence factors and host response modifiers. The emerging, more complex, view of the factors determining course and outcome of infections promises to enable more tailored and thus, hopefully, more effective treatment decisions.

Viable Borrelia burgdorferi enhances interleukin-10 production and suppresses activation of murine macrophages

Although it is capable of eliciting strong innate and adaptive immune responses, Borrelia burgdorferi often evades immune clearance through largely unknown mechanisms. Our previous studies determined that infected interlukin-10-/- (IL-10-/-) mice show significantly lower B. burgdorferi levels than wild-type (B6) mice and that IL-10 inhibits innate immune responses critical for controlling B. burgdorferi infection. To determine whether virulent B. burgdorferi preferentially enhances IL-10 production, we developed an in vitro coculture medium (RPMI.B) in which both B. burgdorferi and primary macrophages (Mphis) remain viable. B. burgdorferi grew at similar rates and was able to regulate expression of immunoreactive proteins with similar kinetics in RPMI.B and in traditional BSK medium; in contrast, B. burgdorferi cultured in conventional tissue culture medium (RPMI) rapidly lost viability. Coculture of viable B. burgdorferi in RPMI.B with Mphis resulted in more rapid and significant increases in IL-10 transcripts and secreted proteins than coculture with nonviable B. burgdorferi in RPMI, which corresponded with decreased production of proinflammatory cytokines. Addition of live B. burgdorferi to Mphis in RPMI.B also elicited substantially higher IL-10 levels than heat-killed bacteria elicited, confirming that increased IL-10 production was not inherent to coculture in RPMI.B. Transfer of supernatants from B. burgdorferi-stimulated Mphis into naïve Mphi cultures resulted in suppressed activation upon subsequent stimulation with different bacterial agonists, and this suppression was obviated by IL-10-specific antibody. In vivo analyses determined that murine skin samples exhibited substantial upregulation of IL-10 within 24 h of injection of B. burgdorferi. Together, these results suggest that viable B. burgdorferi can suppress early Mphi responses during infection by causing increased release of IL-10.

Pro-inflammatory action of LDL(−) on mononuclear cells is counteracted by increased IL10 production

OBJECTIVE

LDL(-) is a minor LDL subfraction that induces inflammatory factor release by endothelial cells. Since LDL(-) is present in plasma, its interaction with leucocytes, a cell type involved in atherosclerosis phenomena, is feasible; therefore, the aim of the current study was to evaluate LDL(-) effect on lymphocytes and monocytes isolated from human plasma.

METHODS AND RESULTS

Mononuclear cells were incubated with LDL(+) and LDL(-) and expression and release of several inflammatory mediators were analyzed by protein membrane assay, ELISA and real-time RT-PCR. LDL(-) induced a significantly increased production versus LDL(+) in MCP1, GRObeta, GROgamma, IL6, IL8 and IL10 in monocytes as well as in lymphocytes. These induced molecules are inflammatory, except for IL10 which is considered an anti-inflammatory cytokine. Therefore, the role of IL10 was evaluated in experiments where exogenous IL10 or antibodies anti-IL10 or anti-IL10 receptor were added. IL10 addition diminished the release of the other factors induced by LDL(-) near to basal production both at protein and RNA level. In contrast, the antibody anti-IL10 increased inflammatory cytokine release around two-fold, whereas the antibody anti-IL10 receptor produced a lower effect.

CONCLUSIONS

LDL(-) promoted inflammatory cytokine production in leucocytes; however, it also induced IL10 that minimized this effect. Therefore, IL10 developed a significant role in counteracting the LDL(-) inflammatory action.

Propensity to excessive proinflammatory response in chronic Lyme borreliosis

The clinical course of Lyme borreliosis is extremely variable. However, all the clinical manifestations, acute or chronic, are characterized by strong inflammation. Borrelia burgdorferi can induce the production of several proinflammatory and anti-inflammatory cytokines. The aim of our study was to find out whether the balance between inflammatory and regulatory mechanisms is important in determining the course of Lyme borreliosis. 13 patients with early Lyme borreliosis, 8 patients with chronic Lyme disease with neurological or joint manifestations, and 15 age- and sex-matched healthy controls were studied. Chronic forms of Lyme borreliosis were characterized by stronger TNF-alpha response by monocytes to lipopolysaccharide as well as to borrelia antigen compared to early Lyme borreliosis and the healthy state. The percentage of IL-10-secreting monocytes in response to borrelia lysate was lower in the Lyme borreliosis patients than in healthy controls. The percentage of CD4(+) CTLA-4(+) regulatory T cells showed the highest values in early Lyme borreliosis. We conclude that chronic forms of Lyme borreliosis can evolve due to an aberrant innate proinflammatory response.

Monocyte p110alpha phosphatidylinositol 3-kinase regulates phagocytosis, the phagocyte oxidase, and cytokine production

Mononuclear phagocytes are critical modulators and effectors of innate and adaptive immune responses, and PI-3Ks have been shown to be multifunctional monocyte regulators. The PI-3K family includes eight catalytic isoforms, and only limited information is available about how these contribute to fine specificity in monocyte cell regulation. We examined the regulation of phagocytosis, the phagocyte oxidative burst, and LPS-induced cytokine production by human monocytic cells deficient in p110alpha PI-3K. We observed that p110alpha PI-3K was required for phagocytosis of IgG-opsonized and nonopsonized zymosan in differentiated THP-1 cells, and the latter was inhibitable by mannose. In contrast, p110alpha PI-3K was not required for ingestion serum-opsonized zymosan. Taken together, these results suggest that FcgammaR- and mannose receptor-mediated phagocytosis are p110alpha-dependent, whereas CR3-mediated phagocytosis involves a distinct isoform. It is notable that the phagocyte oxidative burst induced in response to PMA or opsonized zymosan was also found to be dependent on p110alpha in THP-1 cells. Furthermore, p110alpha was observed to exert selective and bidirectional effects on the secretion of pivotal cytokines. Incubation of p110alpha-deficient THP-1 cells with LPS showed that p110alpha was required for IL-12p40 and IL-6 production, whereas it negatively regulated the production of TNF-alpha and IL-10. Cells deficient in p110alpha also exhibited enhanced p38 MAPK, JNK, and NF-kappaB phosphorylation. Thus, p110alpha PI-3K appears to uniquely regulate important monocyte functions, where other PI-3K isoforms are uninvolved or unable to fully compensate.

Role of interleukin 10 during persistent infection with the relapsing fever Spirochete Borrelia turicatae

Relapsing fever is an infection characterized by peaks of spirochetemia attributable to antibody selection against variable serotypes. In the absence of B cells, serotypes cannot be cleared, resulting in persistent infection. We previously identified differences in spirochetemia and disease severity during persistent infection of severe combined immunodeficiency mice with isogenic serotypes 1 (Bt1) or 2 (Bt2) of Borrelia turicatae. To investigate this further, we studied pathogen load, clinical disease, cytokine/chemokine production, and inflammation in mice deficient in B (Igh6-/-) or B and T (Rag1-/-) cells persistently infected with Bt1 or Bt2. The results showed that Igh6-/- mice, despite lower spirochetemia, had a significantly aggravated disease course compared with Rag1-/- mice. Measurement of cytokines revealed a significant positive correlation between pathogen load and interleukin (IL)-10 in blood, brain, and heart. Bt2-infected Rag1-/- mice harbored the highest spirochetemia and, at the same time, displayed the highest IL-10 plasma levels. In the brain, Bt1, which was five times more neurotropic than Bt2, caused higher IL-10 production. Activated microglia were the main source of IL-10 in brain. IL-10 injected systemically reduced disease and spirochetemia. The results suggest IL-10 plays a protective role as a down-regulator of inflammation and pathogen load during infection with relapsing fever spirochetes.

Cell adhesion on nanofibrous polytetrafluoroethylene (nPTFE)

Here, we described the in vitro biocompatibility of a novel nanostructured surface composed of PTFE as a potential polymer for the prevention of adverse host reactions to implanted devices. The foreign body response is characterized at the tissue-material interface by several layers of macrophages and large multinucleated cells known as foreign body giant cells (FBGC), and a fibrous capsule. The nanofibers of nanofibrous PTFE (nPTFE) range in size from 20 to 30 nm in width and 3-4 mm in length. Glass surfaces coated with nPTFE (produced by jet-blowing of PTFE 601A) were tested under in vitro conditions to characterize the amount of protein adsorption, cell adhesion, and cell viability. We have shown that nPTFE adsorbs 495 +/- 100 ng of bovine serum albumin (BSA) per cm2. This level was considerably higher than planar PTFE, most likely due to the increase in hydrophobicity and available surface area, both a result of the nanoarchitecture. Endothelial cells and macrophages were used to determine the degree of cell adsorption on the surface of the nanostructured polymer. Both cell types were significantly more round and occupied less area on nPTFE as compared to tissue culture polystyrene (TCPS). Furthermore, a larger majority of the cells on the nPTFE were dead compared to TCPS, at dead-to-live ratios of 778 +/- 271 to 1 and 23 +/- 5.6 to 1, respectively. Since there was a high amount of cell death (due to either apoptosis or necrosis), and the foreign body response is a form of chronic inflammation, an 18 cytokine Luminex panel was performed on the supernatant from macrophages adherent on nPTFE and TCPS. As a positive control for inflammation, lipopolysaccharide (LPS) was added to macrophages on TCPS to estimate the maximum inflammation response of the macrophages. From the data presented with respect to IL-1, TNF-alpha, IFN-gamma, and IL-5, we concluded that nPTFE is nonimmunogenic and should not yield a huge inflammatory response in vivo, and cell death observed on the surface of nPTFE was likely due to apoptosis resulting from the inability of cells to spread on these surface. On the basis of the production of IL-1, IL-6, IL-4, and GM-CSF, we concluded that FBGC formation on nPTFE may be decreased as compared to materials known to elicit FBGC formation in vivo.

Interleukin-10 anti-inflammatory response to Borrelia burgdorferi, the agent of Lyme disease: a possible role for suppressors of cytokine signaling 1 and 3

It has been established that interleukin-10 (IL-10) inhibits inflammatory cytokines produced by macrophages in response to Borrelia burgdorferi or its lipoproteins. The mechanism by which IL-10 exerts this anti-inflammatory effect is still unknown. Recent findings indicate that suppressors of cytokine signaling (SOCS) proteins are induced by cytokines and Toll-like receptor (TLR)-mediated stimuli, and in turn they can down-regulate cytokine and TLR signaling in macrophages. Because it is known that SOCS are induced by IL-10 and that B. burgdorferi and its lipoproteins most likely interact via TLR2 or the heterodimers TLR2/1 and/or TLR2/6, we hypothesized that SOCS are induced by IL-10 and B. burgdorferi and its lipoproteins in macrophages and that SOCS may mediate the inhibition by IL-10 of concomitantly elicited cytokines. We report here that mouse J774 macrophages incubated with IL-10 and added B. burgdorferi spirochetes (freeze-thawed, live, or sonicated) or lipidated outer surface protein A (L-OspA) augmented their SOCS1/SOCS3 mRNA and protein expression, with SOCS3 being more abundant. Pam(3)Cys, a synthetic lipopeptide, also induced SOCS1/SOCS3 expression under these conditions, but unlipidated OspA was ineffective. Neither endogenous IL-10 nor the translation inhibitor cycloheximide blocked SOCS1/SOCS3 induction by B. burgdorferi and its lipoproteins, indicating that the expression of other genes is not required. This temporally correlated with the IL-10-mediated inhibition of the inflammatory cytokines IL-1beta, IL-6, IL-12p40, IL-18, and tumor necrosis factor alpha. Our data are evidence to suggest that expression of SOCS is part of the mechanism of IL-10-mediated inhibition of inflammatory cytokines elicited by B. burgdorferi and its lipoproteins.

Lipoprotein-dependent and -independent immune responses to spirochetal infection

In this study, we used the epidermal suction blister technique, in conjunction with multiparameter flow cytometry, to analyze the cellular and cytokine responses elicited by intradermal injection of human volunteers with synthetic analogs for spirochetal lipoproteins and compared the responses to findings previously reported from patients with erythema migrans (EM). Compared with peripheral blood (PB), lipopeptides derived from the N termini of the Borrelia burgdorferi outer surface protein C and the 17-kDa lipoprotein of Treponema pallidum (OspC-L and 17-L, respectively) elicited infiltrates enriched in monocytes/macrophages and dendritic cells (DCs) but also containing substantial percentages of neutrophils and T cells. Monocytoid (CD11c(+)) and plasmacytoid (CD11c(-)) DCs were selectively recruited to the skin in ratios similar to those in PB, but only the former expressed the activation/maturation surface markers CD80, CD83, and DC-SIGN. Monocytes/macrophages and monocytoid DCs, but not plasmacytoid DCs, displayed significant increases in surface expression of Toll-like receptor 1 (TLR1), TLR2, and TLR4. Staining for CD45RO and CD27 revealed that lipopeptides preferentially recruited antigen-experienced T-cell subsets; despite their lack of antigenicity, these agonists induced marked T-cell activation, as evidenced by surface expression of CD69, CD25, and CD71. Lipopeptides also induced significant increases in interleukin 12 (IL-12), IL-10, gamma interferon, and most notably IL-6 without corresponding increases in serum levels of these cytokines. Although lipopeptides and EM lesional infiltrates shared many similarities, differences were noted in a number of immunologic parameters. These studies have provided in situ evidence for a prominent "lipoprotein effect" during human infection while at the same time helping to pinpoint aspects of the cutaneous response that are uniquely driven by spirochetal pathogens.

IL-10-dependent down-regulation of MHC class II expression level on monocytes by peritoneal fluid from endometriosis patients

Endometriosis is a gynecologic disorder characterized by the ectopic growth of misplaced endometrial cells. Moreover, immunological abnormalities of cell-mediated and humoral immunity may be associated with the pathogenesis of endometriosis. The effects of peritoneal fluid (PF) from endometriosis patients on the expression levels of MHC class II and costimulatory molecules on the cell surfaces of monocytes were investigated. Compared to the PF of controls, the addition of 10% PF (n=10) from patients with endometriosis to culture medium significantly reduced the percentage of MHC class II-positive cells in cultures of a THP-1, monocytic cell line at 48 h. The effect of endometriosis patient PF (EPF) was dose-dependent, and similar effect was observed in peripheral blood monocytes. An inverse correlation was found between MHC class II expression level and IL-10 concentration in EPF (r=-0.518; p=0.019) and in the supernatant of peripheral blood monocyte cultured in EPF (r=-0.459; p=0.042) (n=20). The expression levels of costimulatory molecules (CD80 and CD86), but not of CD54 and B7-H1, were down-regulated by EPF. The mRNA level of HLA-DR was unaffected by EPF but protein level was reduced by EPF. Neutralizing IL-10 antibody abrogated MHC class II down-regulation on monocytes, which had been induced by EPF. However, in a functional assay, monocytes treated with EPF failed to stimulate T cell in mixed leukocyte reaction, although T cell proliferation was increased with EPF-treated monocytes and Staphylococcus enterotoxin B. These results suggest that MHC class II expression level on monocytes is down-regulated by EPF, but the cell stimulatory ability of monocytes does not coincide with MHC class II expression level.

Immunochemical analysis of lipopolysaccharide-like component extracted from Borrelia burgdorferi sensu lato

Immunoelectrophoresis and its modifications were applied to analysis of a lipopolysaccharide-like component (LPS-LC) extracted from Borrelia garinii strains K24 and K48 isolated from Ixodes ricinus and Borrelia burgdorferi sensu stricto strain B31. A modification of the hot phenol-water method was used for isolation of LPS. Immunoelectrophoresis (IE) and crossed immunoelectrophoresis (CIE) of LPS-LC with polyclonal rabbit antisera revealed a pattern and properties partially similar to LPS from other Gram-negative bacteria. B. garinii LPS-LC formed in CIE a diffuse band extending from the start to the anode. Similarly, the shape and position of the band in IE did not show major differences from LPS of other Gram-negative bacteria. The LPS-LC extracted from the three genomic groups of B. burgdorferi sensu lato were found to have similar immunochemical properties irrespective of their genotype origin.

Influence of pathological progression on the balance between cellular and humoral immune responses in bovine tuberculosis

Studies of tuberculosis have suggested a shift in dominance from a T helper type 1 (Th1) towards a Th2 immune response that is associated with suppressed cell-mediated immune (CMI) responses and increased humoral responses as the disease progresses. In this study a natural host disease model was used to investigate the balance of the evolving immune response towards Mycobacterium bovis infection in cattle with respect to pathogenesis. Cytokine analysis of CD4 T-cell clones derived from M. bovis-infected animals gave some indication that there was a possible relationship between enhanced pathogenesis and an increased ratio of Th0 [interleukin-4-positive/interferon-gamma-positive (IL-4(+)/IFN-gamma(+))] clones to Th1 (IFN-gamma(+)) clones. All animals developed strong antimycobacterial CMI responses, but depressed cellular responses were evident as the disease progressed, with the IFN-gamma test failing to give consistently positive results in the latter stages. Furthermore, a stronger Th0 immune bias, depressed in vitro CMI responses, elevated levels of IL-10 expression and enhanced humoral responses were also associated with increased pathology. In minimal disease, however, a strong Th1 immune bias was maintained and an anti-M. bovis humoral response failed to develop. It was also seen that the level of the anti-M. bovis immunoglobulin G1 (IgG1) isotype antibody responses correlated with the pathology scores, whereas CMI responses did not have as strong a relationship with the development of pathology. Therefore, the development and maintenance of a Th1 IFN-gamma response is associated with a greater control of M. bovis infection. Animals progressing from a Th1-biased to a Th0-biased immune response developed more extensive pathology and performed less well in CMI-based diagnostic tests but developed strong IgG1 humoral responses.

Lipoproteins, not lipopolysaccharide, are the key mediators of the proinflammatory response elicited by heat-killed Brucella abortus

Inflammation is a hallmark of brucellosis. Although Brucella abortus, one of the disease's etiologic agents, possesses cytokine-stimulatory properties, the mechanism by which this bacterium triggers a proinflammatory response is not known. We examined the mechanism whereby heat-killed B. abortus (HKBA), as well as its LPS, induces production of inflammatory cytokines in monocytes/macrophages. Polymyxin B, a specific inhibitor of LPS activity, did not inhibit the production of TNF-alpha- and IL-6-induced HKBA in the human monocytic cell line THP-1. HKBA induced the production of these cytokines in peritoneal macrophages of both C3H/HeJ and C3H/HeN mice, whereas B. abortus LPS only stimulated cells from C3H/HeN mice. Anti-TLR2 Ab, but not anti-TLR4 Ab, blocked HKBA-mediated TNF-alpha and IL-6 production in THP-1 cells. Because bacterial lipoproteins, a TLR2 ligand, have potent inherent stimulatory properties, we investigated the capacity of two B. abortus lipoproteins, outer membrane protein 19 (Omp19) and Omp16, to elicit a proinflammatory response. Lipidated (L)-Omp16 and L-Omp19, but not their unlipidated forms, induced the secretion of TNF-alpha, IL-6, IL-10, and IL-12 in a time- and dose-dependent fashion. Preincubation of THP-1 cells with anti-TLR2 Ab blocked L-Omp19-mediated TNF-alpha and IL-6 production. Together, these results entail a mechanism whereby B. abortus can stimulate cells from the innate immune system and induce cytokine-mediated inflammation in brucellosis. We submit that LPS is not the cause of inflammation in brucellosis; rather, lipoproteins of this organism trigger the production of proinflammatory cytokines, and TLR2 is involved in this process.

Inflammatory antigens of Brugia malayi and their effect on rodent host Mastomys coucha

The study was aimed at identifying pro- and anti-inflammatory cytokine releasing potential of Brugia malayi adult worm fractions and their role in filarial infection and pathogenesis. THP-1 cells were incubated with soluble somatic Brugia malayi adult worm extract (BmAS) and its Sephadex G-200 fractions BmAFI, BmAFII and BmAFIII and the effect of the fractions on parasitological, immunological and lymph node parameters was assessed in Mastomys coucha. BmAFII stimulated the pro-inflammatory TNF-alpha, IL-1beta and IL-6 release; IL-10 release was insignificant. Sensitization of animals with BmAFII and subsequent intraperitoneal implantation of worms enhanced CMI response. BmAFII also increased lymph node weight and cellularity, stimulated lymph node mast cells and eliminated intraperitoneally instilled worms. BmAFI stimulated several folds more release of IL-10, whereas TNF-alpha release was negligible. Sensitization with BmAFI elicited low CMI responses, moderately stimulated mast cells and facilitated survival of implanted adult parasites. Fifty percent of naive animals exposed to BmAFI showed oedematous lymph nodes and increased node weight. NCP-bound molecules corresponding to BmAFI and II showed cytokine-stimulating potential in vitro. It is concluded that BmAFII is protective and stimulates pro-inflammatory cytokines, whereas BmAFI facilitates parasite survival and stimulates IL-10.

Inhibition of NF-kappaB activation in macrophages increases atherosclerosis in LDL receptor-deficient mice

Atherosclerosis is now generally accepted as a chronic inflammatory condition. The transcription factor NF-kappaB is a key regulator of inflammation, immune responses, cell survival, and cell proliferation. To investigate the role of NF-kappaB activation in macrophages during atherogenesis, we used LDL receptor-deficient mice with a macrophage-restricted deletion of IkappaB kinase 2 (IKK2), which is essential for NF-kappaB activation by proinflammatory signals. These mice showed increased atherosclerosis as quantified by lesion area measurements. In addition, the lesions were more advanced and showed more necrosis and increased cell number in early lesions. Southern blotting revealed that deletion of IKK2 was approximately 65% in macrophages, coinciding with a reduction of 50% in NF-kappaB activation, as compared with controls. In both groups, the expression of differentiation markers, uptake of bacteria, and endocytosis of modified LDL was similar. Upon stimulation with LPS, production of TNF was reduced by approximately 50% in IKK2-deleted macrophages. Interestingly, we also found a major reduction in the anti-inflammatory cytokine IL-10. Our data show that inhibition of the NF-kappaB pathway in macrophages leads to more severe atherosclerosis in mice, possibly by affecting the pro- and anti-inflammatory balance that controls the development of atherosclerosis.

Borrelia burgdorferi-induced tolerance as a model of persistence via immunosuppression

If left untreated, infection with Borrelia burgdorferi sensu lato may lead to chronic Lyme borreliosis. It is still unknown how this pathogen manages to persist in the host in the presence of competent immune cells. It was recently reported that Borrelia suppresses the host's immune response, thus perhaps preventing the elimination of the pathogen (I. Diterich, L. Härter, D. Hassler, A. Wendel, and T. Hartung, Infect. Immun. 69:687-694, 2001). Here, we further characterize Borrelia-induced immunomodulation in order to develop a model of this anergy. We observed that the different Borrelia preparations that we tested, i.e., live, heat-inactivated, and sonicated Borrelia, could desensitize human blood monocytes, as shown by attenuated cytokine release upon restimulation with any of the different preparations. Next, we investigated whether these Borrelia-specific stimuli render monocytes tolerant, i.e. hyporesponsive, towards another Toll-like receptor 2 (TLR2) agonist, such as lipoteichoic acid from gram-positive bacteria, or towards the TLR4 agonist lipopolysaccharide. Cross-tolerance towards all tested stimuli was induced. Furthermore, using primary bone marrow cells from TLR2-deficient mice and from mice with a nonfunctional TLR4 (strain C3H/HeJ), we demonstrated that the TLR2 was required for tolerance induction by Borrelia, and using neutralizing antibodies, we identified interleukin-10 as the key mediator involved. Although peripheral blood mononuclear cells tolerized by Borrelia exhibited reduced TLR2 and TLR4 mRNA levels, the expression of the respective proteins on monocytes was not decreased, ruling out the possibility that tolerance to Borrelia is attributed to a reduced TLR2 expression. In summary, we characterized tolerance induced by B. burgdorferi, describing a model of desensitization which might mirror the immunosuppression recently attributed to the persistence of Borrelia in immunocompetent hosts.