Influence of lipopolysaccharide exposure on airway function and allergic responses in developing mice

Asthma-protective agents in dust from traditional farm environments

BACKGROUND

Growing up on traditional European or US Amish dairy farms in close contact with cows and hay protects children against asthma, and airway administration of extracts from dust collected from cowsheds of those farms prevents allergic asthma in mice.

OBJECTIVES

This study sought to begin identifying farm-derived asthma-protective agents.

METHODS

Our work unfolded along 2 unbiased and independent but complementary discovery paths. Dust extracts (DEs) from protective and nonprotective farms (European and Amish cowsheds vs European sheep sheds) were analyzed by comparative nuclear magnetic resonance profiling and differential proteomics. Bioactivity-guided size fractionation focused on protective Amish cowshed DEs. Multiple in vitro and in vivo functional assays were used in both paths. Some of the proteins thus identified were characterized by in-solution and in-gel sodium dodecyl sulfate-polyacrylamide gel electrophoresis enzymatic digestion/peptide mapping followed by liquid chromatography/mass spectrometry. The cargo carried by these proteins was analyzed by untargeted liquid chromatography-high-resolution mass spectrometry.

RESULTS

Twelve carrier proteins of animal and plant origin, including the bovine lipocalins Bos d 2 and odorant binding protein, were enriched in DEs from protective European cowsheds. A potent asthma-protective fraction of Amish cowshed DEs (≈0.5% of the total carbon content of unfractionated extracts) contained 7 animal and plant proteins, including Bos d 2 and odorant binding protein loaded with fatty acid metabolites from plants, bacteria, and fungi.

CONCLUSIONS

Animals and plants from traditional farms produce proteins that transport hydrophobic microbial and plant metabolites. When delivered to mucosal surfaces, these agents might regulate airway responses.

Supercritical Fluid-Assisted Porous Microspheres for Efficient Delivery of Insulin and Inhalation Therapy of Diabetes

Pulmonary delivery of drugs has attracted increasing attention in healthcare, as the lungs are an easily accessible site for noninvasive systemic delivery of drugs. Although pulmonary inhalation of porous microparticles has been shown to sustain drug delivery, there are limited reports on efficient delivery of insulin and inhalation therapy of diabetes based on supercritical carbon dioxide (SC-CO₂ ) technology. Herein, this study reports the fabrication of insulin-loaded poly-l-lactide porous microspheres (INS-PLLA PMs) by using the SC-CO₂ technology, and their use as an inhalation delivery system potentially for diabetes therapy. Biocompatibility and delivery efficiency of the PLLA PMs in the lungs are investigated. The PLLA PMs show negligible toxicity to lung-derived cells, resulting in no significant reduction in cell viability, as well as levels of various inflammatory mediators such as interleukin (IL)-6, IL-8, and tumor necrosis factor-α, compared with the negative control group. INS-PLLA PMs are further efficiently deposited in the trachea and the bronchi of superior lobes of the lungs, which exhibit pronounced hypoglycemic activity in induced diabetic rats. Together, the results demonstrate that the INS-PLLA PMs have a strong potential as an effective strategy for inhalation treatment of diabetes.

Supercritical Fluid-Assisted Decoration of Nanoparticles on Porous Microcontainers for Codelivery of Therapeutics and Inhalation Therapy of Diabetes

The impact of nanotechnology and its advancements have allowed us to explore new therapeutic modalities. To this end, we designed nanoparticles-inlaid porous microparticles (NIPMs) coloaded with small interfering RNA (siRNA) and glucagon-like peptide-1 (GLP-1) using the supercritical carbon dioxide (SC-CO₂) technology as an inhalation delivery system for diabetes therapy. siRNA-encapsulating chitosan (CS) nanoparticles were first synthesized by an ionic gelation method, which resulted in particles with small sizes (100-150 nm), high encapsulation efficiency (∼94.8%), and sustained release performance (∼60% in 32 h). These CS nanoparticles were then loaded with GLP-1-dispersed poly-l-lactide (PLLA) porous microparticles (PMs) by SC-CO₂-assisted precipitation with the compressed antisolvent (PCA) process. The hypoglycemic efficacy of NIPMs administered via pulmonary route in mice persisted longer due to sustained release of siRNA from CS nanoparticles and the synergistic effects of GLP-1 in PMs, which significantly inhibited the expression of dipeptidyl peptidase-4 mRNA (DPP-4-mRNA). This ecofriendly technology provides a convenient way to fabricate nanoparticle-microparticle composites for codelivery of a gene and a therapeutic peptide, which will potentially find widespread applications in the field of pharmaceutics.

Lipopolysaccharide Exposure Alleviates Asthma in Mice by Regulating Th1/Th2 and Treg/Th17 Balance

Background

It is generally believed that endotoxin exposure exacerbates risk of developing asthmatic symptoms. However, recent studies have indicated that prior bacterial exposure may prevent future symptoms of asthma. Here, we evaluated the influence of pre-exposure to different concentrations of lipopolysaccharide (LPS) to subsequent ovalbumin (OVA) allergen sensitization and challenge.

Material/Methods

Four-week-old Balb/c mice were treated intranasally with varying concentrations of LPS (1 ug, 10 ug, and 100 ug) or sterile PBS for 10 days, then 2 weeks later they were exposed to OVA. Both the molecular and functional airway responses to OVA administration were assessed following prior exposure to different doses of LPS or controls. Additionally, the Th1/Th2 and Treg/Th17 balance was measured.

Results

Airway responsiveness and immune cell recruitment in the bronchoalveolar lavage (BALF) were decreased in animals exposed to a low dose of LPS (1 ug) treatment compared with the asthma group. Moderate-dose (10 ug) and high-dose (100 ug) LPS administration showed no differences from controls. Further, low-dose LPS (1 ug) exposure was associated with increased Th1 cytokines, T-bet, Treg cytokine (IL-10, TGF-β), and Foxp3 expression, but decreased Th2 cytokines (IL-4,5,13), GATA3, Th17, and ROR-γt expression compared with the asthma group. Finally, higher numbers of CD4+CD25+Foxp3+Treg cells, and CD4+INF-γ+T cells, and lower CD4+IL-4+T cells and CD4+IL-17+T cells were observed in the low-dose LPS-treated groups compared to controls.

Conclusions

Our findings suggest that prior exposure to low doses of LPS may protect from OVA-induced airway hyperresponsiveness (AHR) and histopathologic changes through regulation of the Th1/Th2 and Treg/Th17 balance.

Role of lipopolysaccharide (LPS) in asthma and other pulmonary conditions

Endotoxin significantly contaminates house dust and is an enhancing factor for asthma severity. Natural exposure to endotoxin in early life could influence immune development and protect from the risk of developing atopy. This article will focus on published data showing that home environmental contamination by endotoxin can participate in chronic airways diseases, in particular asthma.

The lung: the natural boundary between nature and nurture

Common lung diseases such as asthma, COPD, and pulmonary fibrosis cause significant morbidity and mortality in the U.S. and worldwide. Research investigating the mechanisms of disease etiology has clearly indicated that genetic attributes and environmental exposures each play important roles in the development of these diseases. Emerging evidence underscores the importance of the interplay between genetic predisposition and environmental factors in fully understanding the development of lung disease. Herein we discuss recent advances in knowledge and technology surrounding the role of genetics, the environment, and gene-environment interactions in these common lung diseases.

Immunomodulating effects of endotoxin in mouse models of allergic asthma

Endotoxin or lipopolysaccharide (LPS) is a cell wall component of Gram-negative bacteria. Like aeroallergens, LPS is ubiquitous in our living environment. Epidemiology studies in young children have found that LPS exposure at home is inversely correlated with the development of atopic diseases, thus the 'hygiene hypothesis' for allergic diseases. However, positive association has also been found between indoor LPS exposure and the development of wheezing or asthma in children. In humans, experimental exposure to LPS in the airways can cause inflammatory responses and lung function changes directly or modulate responses to allergens indirectly, particularly in those with asthma. In animal studies, experimental exposure to LPS has generated some conflicting, sometimes opposite, results in host responses to allergen stimulation. In this article, we will review recent advances in our understanding of the immunomodulating effects of LPS on allergen-induced responses and analyse some of the possible reasons for the inconsistent findings.

Protease-activated receptors and prostaglandins in inflammatory lung disease

Protease-activated receptors (PARs) are a novel family of G protein-coupled receptors. Signalling through PARs typically involves the cleavage of an extracellular region of the receptor by endogenous or exogenous proteases, which reveals a tethered ligand sequence capable of auto-activating the receptor. A considerable body of evidence has emerged over the past 20 years supporting a prominent role for PARs in a variety of human physiological and pathophysiological processes, and thus substantial attention has been directed towards developing drug-like molecules that activate or block PARs via non-proteolytic pathways. PARs are widely expressed within the respiratory tract, and their activation appears to exert significant modulatory influences on the level of bronchomotor tone, as well as on the inflammatory processes associated with a range of respiratory tract disorders. Nevertheless, there is debate as to whether the principal response to PAR activation is an augmentation or attenuation of airways inflammation. In this context, an important action of PAR activators may be to promote the generation and release of prostanoids, such as prostglandin E(2), which have well-established anti-inflammatory effects in the lung. In this review, we primarily focus on the relationship between PARs, prostaglandins and inflammatory processes in the lung, and highlight their potential role in selected respiratory tract disorders, including pulmonary fibrosis, asthma and chronic obstructive pulmonary disease.

The role of infection in asthma

This paper reviews the impact of infections on the onset and clinical course of bronchial asthma. A just emphasis is given to the role viral infections, particularly rhinovirus infections, play in exacerbations, and that played by respiratory syncytial virus, suspected of triggering the asthmatic syndrome. The mechanisms of the immune response to virus attacks are explained, highlighting the asthmatic and allergic patient's weakened response, particularly in the perinatal period. Further stressed is a potentiating effect of viral aggression on the allergic response. The hygiene hypothesis and its lack of scientific consistency is detailed, at least as far as the role it seeks to confer on an unproven antagonism of the Th1 and Th2 lymphocyte responses. The current importance of research not into bacteria, but into bacterial products, including endotoxins, on the modulation of asthma and allergy is noted. Studies which, along these lines, show an environmental impact on genetic secretion in the phenotype are underlined. Also discussed in passing are several mechanisms which go towards explaining neutrophilic asthma - for many a contradiction, given eosinophilia's stranglehold on asthmatic inflammation.

Infecção na modulaçâo da asma11Trabalho apresentado no XXIII Congresso de Pneumologia da SPP – Guarda, Novembro 2007 / Paper presented at the XXIII Congresso de Pneumologia da SPP / PSP Pulmonology Congress, Guarda, November 2007

Faz-se uma revisão da influência das infecções no aparecimento e na clínica da asma brônquica. Dá-se o relevo que merece à intervenção virusal, sobretudo ao rinovírus, pela sua influência nas exacerbações, e ao vírus sincicial respiratório, sobre o qual recai a suspeita de poder ser causa determinante no aparecimento da síndroma asmática. Tentam-se esclarecer os mecanismos da resposta imune à agressão virusal em função das debilidades da resposta do asmático e do atópico, sobretudo no período perinatal, salientando-se, ainda, um efeito de potenciação da agressão virusal sobre a resposta atópica. Aborda-se a hipótese higiénica e a sua falta de consistência científica, pelo menos no papel que pretende atribuir a um não demonstrado antagonismo das respostas linfocitárias Th₁ e Th_2, apontando-se a importância actual da investigação, não das bactérias mas dos produtos bacterianos, como as endotoxinas, na modulação da asma e da atopia, dando-se relevo aos estudos que, a partir deste modelo, demonstram uma influência do ambiente na secreção génica e, consequentemente, no fenótipo. Invocam-se, nas entrelinhas, vários mecanismos que podem explicar a asma neutrofílica que, para muitos, é um paradoxo perante o consagrado domínio do eosinófilo na inflamação asmática.

Rev Port Pneumol 2008; XIV (5): 647-675

T-cell responses to allergens

The allergic response in human beings is engineered by CD4(+) T lymphocytes, which secrete T(H)2 cytokines in response to activation by allergen-derived peptides. Although T(H)2 cells have been well characterized, defining the properties of allergen-specific T cells has proved challenging in human beings because of their low frequency within the T-cell repertoire. However, recent studies have provided insight into the molecular signature of long-lived human memory T(H)2 cells, which are allergen-specific. T-cell responses directed against allergens develop in early life and are heavily influenced by the type and dose of allergen, and possibly coexposure to microbial products. These responses are susceptible to suppression by regulatory T cells. This article highlights recent advances in the characterization of allergen-specific memory T(H)2 cells and discusses the heterogeneous nature of regulatory T cells and possible mechanisms of action. The relevance of T-cell epitope mapping studies to understanding the unique nature of T-cell responses to different allergens, as well as to peptide vaccine development, is reviewed. Experimental techniques and approaches for analyzing allergen-specific T cells and identifying novel T-cell epitopes are described that may lead to new T-cell-based therapies.

Lipopolysaccharide exposure makes allergic airway inflammation and hyper-responsiveness less responsive to dexamethasone and inhibition of iNOS

Allergic airway disease can be refractory to anti-inflammatory treatment, whose cause is unclarified. Therefore, in the present experiment, we have tested the hypothesis that co-exposure to lipopolysacharide (Lps) and allergen results in glucocorticoid-resistant eosinophil airway inflammation and hyper-responsiveness (AHR). Ovalbumin (Ova)-sensitized BALB/c mice were primed with 10 microg intranasal Lps 24 h before the start of Ova challenges (20 min on 3 consecutive days). Dexamethasone (5 mg/kg/day) was given on the last 2 days of Ova challenges. AHR, cellular build-up, cytokine and nitrite concentrations of bronchoalveolar lavage fluid (BALF) and lung histology were examined. To assess the role of iNOS-derived NO in airway responsiveness, mice were treated with a selective inhibitor of this enzyme (1400W) 2 h before AHR measurements. More severe eosinophil inflammation and higher nitrite formation were found in Lps-primed than in non-primed allergized mice. After Lps priming, AHR and concentrations of T-helper type 2 cytokines in BALF were decreased, but still remained significantly higher than in controls. Eosinophil inflammation was partially, while nitrite production and AHR were observed to be largely dexamethasone resistant in Lps-primed allergized animals. 1400W effectively and rapidly diminished the AHR in Ova-sensitized and challenged mice, but failed to affect it after Lps priming plus allergization. In conclusion, Lps inhalation may exaggerate eosinophil inflammation and reduce responsiveness to anti-inflammatory treatment in allergic airway disease.

Elevated concentrations of endotoxin in indoor air due to cigarette smoking

Exposure to environmental tobacco smoke (ETS) is an important worldwide public health issue. The present study demonstrates that cigarette smoke can be a major source of endotoxin (lipopolysaccharide, LPS) in indoor environments. Gas-chromatography/mass-spectrometry was used to determine 3-hydroxy fatty acids as markers of endotoxin in air-borne house dust in homes of smokers and non-smokers. Air concentrations of endotoxin were 4-63 times higher in rooms of smoking students than in identical rooms of non-smoking students. The fact that cigarette smoke contains large amounts of endotoxin may partly explain the high prevalence of respiratory disorders among smokers and may also draw attention to a hitherto neglected risk factor of ETS.

Role of cysteinyl leukotrienes in airway inflammation and responsiveness following RSV infection in BALB/c mice

Cysteinyl leukotrienes (CysLTs) contribute to the development of airway obstruction and inflammation in asthma; however little information is available on the role of these molecules in the pathophysiology of respiratory syncytial virus (RSV) bronchiolitis. This study was designed to evaluate the effects of RSV infection on CysLTs production in a well-established mouse infection model. Furthermore, we assessed the effect of anti-inflammatory agents (a leukotriene receptor antagonist, MK-571, and dexamethasone) on the functional and immune changes induced by RSV infection. Six to 8-wk-old BALB/c mice were infected with human RSV (strain A2). Measurements of airway function were performed using whole body plethysmography. Lung inflammation was assessed by cell counts, measurement of cytokines and CysLTs in bronchoalveolar lavage fluid (BALF) in the absence and presence of treatment with MK-571 or dexamethasone. RSV infection produced a marked increase in CysLTs in the BALF and lung tissue, recruitment of neutrophils and lymphocytes into the airways, increased IFN-gamma levels and airway hyperresponsiveness (AHR). Treatment with MK-571 decreased RSV-induced AHR without affecting the cellular and inflammatory responses to RSV. Dexamethasone decreased AHR and markedly reduced the recruitment of inflammatory cells and production of IFN-gamma. Our findings suggest CysLTs play an important role in the pathogenesis of RSV-induced airway dysfunction. Treatment with MK-571 decreases RSV-induced AHR but does not appear to alter the lung inflammatory responses to RSV. In contrast, dexamethasone decreases RSV-induced AHR but interferes with recruitment of inflammatory cells, resulting in decreased Th1 cytokines (a potentially Th2-prone environment) in this model. These studies support recent reports on the beneficial effects of CysLT receptor antagonist in human trials and provide a model for investigating the role of CysLTs in RSV bronchiolitis.

Endotoxin and the lung: Insight into the host-environment interaction

Understanding the pathophysiology and basic mechanisms of asthma and chronic obstructive pulmonary disease (COPD) has been an intense source of investigation over the years. For decades, research in these fields has focused on the control of inflammation. However, new evidence has emerged demonstrating that airway inflammation is just the surface of a more complex pathobiological relationship between the disease and its host. Specifically, the relationship is a unique interaction of one's genetic background and the environment. The airway response to inhaled endotoxin serves as an effective model for studying the pathobiology of asthma as well as the importance of host genetic susceptibility. In this review, we provide a brief overview on the role of endotoxin in asthma and COPD, highlighting a few of the major discoveries, but also discussing future directions.

Pulmonary inflammation caused by chitosan microparticles

Chitosan is a cationic biopolymer derived from chitin with potential therapeutic applications such as controlled drug delivery to mucosal-epithelial surfaces in the body. Inhaled chitosan microparticles (CM), for example, are of potential interest in pulmonary pharmacotherapy. In this context, we examine some basic reactions of lung tissue to CM. Inhaled CM (2-10 mg/kg of particles) induce dose-dependent proinflammatory effects in rat lungs; these effects are documented in increases in bronchoalveolar lavage fluid protein (BALF-P) and lactate dehydrogenase activity (BALF-LDH) and increases in lung tissue myeloperoxidase (MPO) activity and leukocyte migration. Overall, the biochemical parameters (i.e., average of BALF-P, BALF-DH, and MPO) indicate that the inflammation response is 1.8-fold greater than controls without CM; the same inflammation parameters, however, are 1.9-fold lower with CM compared with the proinflammatory effects of lipopolysaccharide (LPS). Cytological examination of BALF shows a large infiltration of polymorphonuclear neutrophils to lung tissue: more than a sixfold increase in this population of inflammatory cells, after inhalation of CM relative to air inhalation controls. Thus, the results indicate that inhaled CM can have significant proinflammatory effects on lung tissues; these effects are mild relative to LPS but need to be considered in the context of therapeutic applications via pulmonary delivery if such concentrations of CM are used.

Airway mucosal thickening and bronchial hyperresponsiveness induced by inhaled beta 2-agonist in mice

BACKGROUND

Patients with chronic persistent asthma require frequent use of inhaled beta(2)-agonist, which may result in aggravation of asthma symptoms. Our recent in vitro study has shown that beta(2)-agonist stimulates the growth of human airway epithelial cell lines.

STUDY OBJECTIVE

To determine whether beta(2)-agonist likewise affects airway epithelial cell proliferation in vivo and, if so, what the mechanism of action is, we examined the effect of salbutamol on the morphology of murine airways.

METHODS

Seventy-two BALB/c mice were administered aerosolized salbutamol using "flow-through" nose-only inhalation chambers at daily doses of 0.2 to 20 microg for up to 6 weeks. Morphology of tracheal mucosa, labeling of epithelial cells with 5-bromo-2'-deoxyuridine (BrdU), and bronchial responsiveness were assessed.

RESULTS

Exposure to salbutamol increased the thickness of tracheal epithelial layer and the number of BrdU-positive epithelial cells in a dose- and time-dependent manner: the values in mice receiving 20 microg salbutamol for 6 weeks were 247% and 642%, respectively, of those in control animals receiving saline solution alone. These effects were inhibited by the mitogen-activated protein (MAP) kinase kinase inhibitors PD98059 and U0126. Salbutamol also caused a decrease in the provocative concentration of methacholine to achieve 400% of baseline enhanced pause. Combined treatment with inhaled budesonide attenuated salbutamol-induced airway morphologic changes and bronchial hyperresponsiveness.

CONCLUSION

beta(2)-agonist stimulates proliferation of airway epithelial cells and produces airway wall thickening in vivo via MAP kinase-dependent pathway, and these effects are prevented by inhaled corticosteroid.

Interleukin-12-independent down-modulation of cockroach antigen-induced asthma in mice by intranasal exposure to bacterial lipopolysaccharide

Several studies have shown that exposure to bacterial lipopolysaccharide (LPS) can either prevent or inhibit asthma in humans and laboratory rodents. Much emphasis has been placed on the role of cytokines and chemokines in the establishment and maintenance of allergic airway disease. Therefore, it is of interest to study the role of LPS in affecting airway pathology and lung cytokine and chemokine responses in the maintenance phase of asthma. Increasing doses of LPS were administered into the airways of mice presensitized with cockroach allergen (CRAg), then allergic airway disease parameters were assessed after CRAg challenge. Airway hyperresponsiveness after antigen challenge decreased at the highest dose of LPS tested, which was accompanied by a decrease in airway and lung eosinophils. However, a dramatic increase in lung inflammation because of neutrophil influx was observed. Measurement of cytokines in lungs of LPS-treated, CRAg-sensitized mice indicated that interleukin (IL)-12 levels were increased by LPS treatment in a dose-dependent manner, as were levels of several inflammatory chemokines. In contrast, levels of IL-4, IL-13, IL-5, and IL-10 were reduced in whole lung homogenates only of high-dose LPS-treated mice. Intranasal administration of neutralizing anti-IL-12 at the time of high-dose LPS challenge reduced lung IL-12, interferon-gamma, CXCL9, and CXCL10 but did not affect levels of the other chemokines or Th2-type cytokines, and did not restore AHR. These findings suggest that the amelioration of airway hyperresponsiveness observed in LPS-treated, CRAg-sensitized mice is coincident with an immune deviation of the lung inflammatory response, independent of IL-12.

Airway responsiveness after acute exposure to urban particulate matter 1648 in a DO11.10 murine model

Enhanced airway responsiveness (AR) is a well-established characteristic of asthma that epidemiological evidence has linked with inhalation of ambient particulate matter (PM). To determine whether acute exposure to urban particulate matter PM1648 can exacerbate airway responsiveness and alter the early inflammatory state, a unique murine model was created using DO11.10 mice, transgenic for a T cell receptor recognizing ovalbumin(323-339). Because these mice are sensitive to ovalbumin, immunization procedures involving adjuvant or long aerosolization procedures are not necessary and, therefore, allow for the study of an acute AR response to particulate and antigen in young animals. AR was assessed by barometric whole body plethysmography and measured by enhanced pause (Penh). PM1648 and ovalbumin were administered intranasally 72 and 4 h before to AR assessment, respectively. A dose-response relationship between PM1648 and Penh was determined, and doses at or above 500 microg had Penh values significantly higher than saline controls. Penh values of control particle titanium dioxide (TiO(2)) were similar to saline controls demonstrating no nonspecific particulate effect on AR. Lung lavage at time of AR assessment showed no significant inflammation due to particulate exposure or ovalbumin alone; however, PM1648/ovalbumin and TiO(2)/ovalbumin combinations resulted in significant neutrophilia. In addition, treatment with polymyxin B to remove surface-bound endotoxin did not significantly affect Penh levels. These results indicate that PM1648 specifically increases AR in a dose-dependent manner and that this exacerbation is not a direct response to increased neutrophil concentration, particle-bound endotoxin or nonspecific particle effects.

At the crossroads of SUMO and NF-kappaB

BACKGROUND

Recognition of pathogens by immune receptors leads to activation of macrophages, dendritic cells, and lymphocytes. Signals are communicated to enhance expression of target molecules such as cytokines and adhesion molecules, depending on activation of various inducible transcription factors, among which the family NF-kappaB transcription factors plays an evolutionarily conserved and critical role. Classical activation of NF-kappaB involves phosphorylation, polyubiquitination and subsequent degradation of the inhibitor molecules of NF-kappaB, referred to as IkappaB. Modification of IkappaBalpha, one of the mammalian IkappaB isoforms, with the small ubiquitin-like modifier (SUMO) results its protection from degradation.

PRESENTATION OF THE HYPOTHESIS

SUMO-IkappaBalpha localizes in the nucleus. The nuclear SUMO-IkappaBalpha pool may be dynamic. SUMO-IkappaBalpha functions as synergy control factor.

TESTING THE HYPOTHESIS

Immunoprecipitation from cellular fractions, 35S methionine pulse-chase, and FRET assays should reveal the localization of SUMO-IkappaBalpha and the dynamics of the pool. Expression of SUMOylation defective IkappaBalpha in an IkappaBalpha -/- background should yield insights into the function of SUMO-IkappaBalpha.

IMPLICATION OF THE HYPOTHESIS

IkappaBalpha contains the required SUMOylation motif but IkappaBbeta does not. The suggested study would provide evidence whether or not IkappaBalpha and IkappaBbeta can substitute each other. In addition, the suggested assays would reveal a possible redundancy in controlling transcriptional activity of NF-kappaB.

Toll-like receptors and T-helper-1/T-helper-2 responses

PURPOSE OF REVIEW

Toll-like receptors (TLRs) are a family of pattern recognition receptors that are activated by specific components of microbes and certain host molecules. They constitute the first line of defense against many pathogens and play a crucial role in the function of the innate immune system. Recently, TLRs were observed to influence the development of adaptive immune responses, presumably by activating antigen-presenting cells. This has important implications for our understanding of how the host tailors its immune response as a function of specific pathogen recognition. The present review discusses the recent studies that demonstrate the role of TLRs in the regulation of adaptive T-helper-1 (Th1) and Th2 responses, and the mechanisms by which the effects are carried out.

RECENT FINDINGS

Most studies have focused on the role of TLRs and components of their signaling pathways in the control of Th1-type immune responses, and on the implications for their use as antimicrobial agents, such as adjuvants in vaccines, or to treat or prevent the Th2-type dominated immune responses seen in allergies. TLR-deficient mice have been described and used to come to these conclusions. Although controversial, there is also evidence that TLRs may be important for Th2-type responses, possibly by augmenting the overall maturity of dendritic cells.

SUMMARY

A greater understanding of the processes by which TLRs regulate adaptive immunity may yield not only improved ways to treat infectious diseases but also new approaches to the treatment and prevention of allergic and certain autoimmune disorders.