Inhibition of T cell costimulation abrogates airway hyperresponsiveness in a murine model

Abatacept to induce remission of peanut allergy during oral immunotherapy (ATARI): protocol for a phase 2a randomized controlled trial

Context

While oral immunotherapy (OIT) has been shown to promote the remission of mild peanut allergy in young children, there is still an unmet need for a disease-modifying intervention for older patients and those with severe diseases. In mice models, abatacept, a cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) immunoglobulin fusion protein, has been shown to promote immune tolerance to food when used as an adjuvant to allergen immunotherapy. The goal of this study is to explore the potential efficacy of abatacept in promoting immune tolerance to food allergens during OIT in humans.

Methods

In this phase 2a proof-of-concept study (NCT04872218), 14 peanut-allergic participants aged from 14 to 55 years will be randomized at a 1:1 ratio to abatacept vs. placebo for the first 24 weeks of a peanut OIT treatment (target maintenance dose of 300 mg peanut protein). The primary outcome will be the suppression of the OIT-induced surge in peanut-specific IgE/total IgE at 24 weeks, relative to the baseline. Sustained unresponsiveness will be assessed as a secondary outcome starting at 36 weeks by observing incremental periods of peanut avoidance followed by oral food challenges.

Discussion

This is the first study assessing the use of abatacept as an adjuvant to allergen immunotherapy in humans. As observed in preclinical studies, the ability of abatacept to modulate the peanut-specific immune response during OIT will serve as a proxy outcome for the development of clinical tolerance, given the small sample size. The study will also test a new patient-oriented approach to sustained tolerance testing in randomized controlled trials.

DNA sequencing validation by PCR-RFLP for evaluating butyrophilin-like 2 rs2076530 polymorphism in Iranian patients with sarcoidosis

BACKGROUND

Sarcoidosis is a multifactorial immune disorder with an uncertain origin. A single nucleotide polymorphism (G→A, rs2076530) in the butyrophilin-like 2 (BTNL2) gene results in the formation of truncating protein. This study aimed to genotype the predisposition of the BTNL2 rs2076530 polymorphism in Iranian patients with sarcoidosis using the RFLP technique.

MATERIALS AND METHODS

In this study, 80 patients with sarcoidosis and 80 healthy individuals were included. The rs2076530 polymorphism of the BTNL2 gene was genotyped using the PCR-RFLP method by AvrII restriction enzyme and confirmed by DNA sequencing (Capillary electrophoresis 3130, ABI).

RESULTS

There was a statistically significant difference between proportions of patients with AA (47,5%) and controls (27.5%) (OR=2.38, 95%CI:1.23-4.61, P=0.009). In addition, a significant difference was observed in the frequency of the A allele (62.5%) in sarcoidosis (OR=2.14, 95%CI:1.37-3.35, P=0.001). A Bonferroni correction with P<0.0038 indicates a statistical difference for genotype AA (P=0.009). In an effective model, binary logistic regression analysis indicates a statistical association between AA genotype and sarcoidosis (P=0.018 with 60% prediction). Based on the gene analysis study using DNA sequencing, all of the mentioned mutations were seen via RFLP.

CONCLUSION

According to our findings, the BTNL2 rs2076530 A allele in the Iranian population is associated with susceptibility to sarcoidosis. This designed PCR-RFLP method for detecting SNPs is effective as DNA sequencing.

Bronchoprovocation Testing in Asthma: An Update

Bronchial hyperresponsiveness (BHR) is defined as a heightened bronchoconstrictive response to airway stimuli. It complements the cardinal features in asthma, such as variable or reversible airflow limitation and airway inflammation. Although BHR is considered a pathophysiologic hallmark of asthma, it should be acknowledged that this property of the airway is dynamic, because its severity and even presence can vary over time with disease activity, triggers or specific exposure, and with treatment. In addition, it is important to recognize that there is a component that is not reflective of a specific disease entity.

Controlled release strategies for modulating immune responses to promote tissue regeneration

Advances in the field of tissue engineering have enhanced the potential of regenerative medicine, yet the efficacy of these strategies remains incomplete, and is limited by the innate and adaptive immune responses. The immune response associated with injury or disease combined with that mounted to biomaterials, transplanted cells, proteins, and gene therapies vectors can contribute to the inability to fully restore tissue function. Blocking immune responses such as with anti-inflammatory or immunosuppressive agents are either ineffective, as the immune response contributes significantly to regeneration, or have significant side effects. This review describes targeted strategies to modulate the immune response in order to limit tissue damage following injury, promote an anti-inflammatory environment that leads to regeneration, and induce antigen (Ag)-specific tolerance that can target degenerative diseases that destroy tissues and promote engraftment of transplanted cells. Focusing on targeted immuno-modulation, we describe local delivery techniques to sites of inflammation as well as systemic approaches that preferentially target subsets of immune populations.

Experimental advances in understanding allergic airway inflammation

Asthma is largely an inflammatory disease, with the development of T cell mediated inflammation in the lung following exposure to allergen or other precipitating factors. Currently, the major therapies for this disease are directed either at relief of bronchoconstriction (ie beta-agonists) or are non-specific immunomodulators (ie, corticosteroids). While much attention has been paid to factors that regulate the initiation of an inflammatory response, chronic inflammation may also be due to defects in regulatory mechanisms that limit or terminate immune responses. In this review, we explore the elements controlling both the recruitment of T cells to the lung and their function. Possibilities for future therapeutic intervention are highlighted.

Interruption of CD28-mediated costimulation during allergen challenge protects mice from allergic airway disease

BACKGROUND

Allergic asthma is a T(H)2-promoted hyperreactivity with an immediate, IgE, and mast cell-dependent response followed by eosinophil-dominated inflammation and airway obstruction.

OBJECTIVE

Because costimulation by CD28 is essential for T(H)2 but not T(H)1 responses, we investigated the effect of selective interference with this pathway in mice using the models of ovalbumin and house dust mite-induced airway inflammation.

METHODS

To study the role of CD28 in the effector phase of allergic airway inflammation, we developed an inducibly CD28-deleting mouse strain or alternatively used a CD28 ligand-binding site-specific mouse anti-mouse mAb blocking CD28 engagement.

RESULTS

We show that even after systemic sensitization to the allergen, interruption of CD28-mediated costimulation is highly effective in preventing airway inflammation during challenge. In addition to improving airway resistance and histopathologic presentation and reducing inflammatory infiltrates, antibody treatment during allergen challenge resulted in a marked relative increase in regulatory T-cell numbers among the CD4 T-cell subset of the challenged lung.

CONCLUSION

Selective interference with CD28-mediated costimulation during allergen exposure might be an attractive therapeutic concept for allergic asthma.

Regulation of cytotoxic T lymphocyte antigen 4 by cyclic AMP

Recent studies indicate that cyclic AMP (cAMP) induces cytotoxic T lymphocyte antigen (CTLA) 4. CTLA4 is expressed in T cells, and is a negative regulator of T cell activation. CTLA4 expression is regulated by T cell receptor plus CD28 (adaptive immune signaling) at both the transcriptional and post-transcriptional level. Here, we examine the pathways by which cAMP regulates CTLA4 expression, focusing on transcriptional activation. Elevating intracellular cAMP levels by cell-permeable cAMP analogs, the adenylyl cyclase activator, forskolin, or phosphodiesterase inhibitors increases CTLA4 mRNA expression in EL4 murine T cells and primary CD4(+) T cells. Activation of protein kinase A (using the protein kinase A-selective agonist, N6-phenyladenosine-cAMP), but not exchange proteins activated by cAMP (using the exchange proteins activated by cAMP-selective 8-pCPT-2Me-cAMP), increases CTLA4 promoter activity. Mutation constructs of the CTLA4 promoter uncover an enhancer binding site located within the -150 to -130 bp region relative to the transcription start site. Promoter analysis and chromatin immunoprecipitation assays suggest that cAMP response element-binding is a putative transcription factor induced by cAMP. We have previously shown that CTLA4 mediates decreased pulmonary inflammation in an LPS-induced murine model of acute lung injury (ALI). We observed that LPS can induce CTLA4 transcription via the same cAMP-inducible promoter region. The immunosuppressant, rapamycin, decreases cAMP and LPS-induced CTLA4 transcription in vitro. In vivo, LPS induces cAMP accumulation in bronchoalveolar lavage fluid, bronchoalveolar lavage cells, and lung tissues in ALI. We demonstrate that rapamycin decreases cAMP accumulation and CTLA4 expression in ALI. Together, these data suggest that cAMP may negatively regulate pulmonary inflammatory responses in vivo and in vitro by altering CTLA4 expression.

PKC-theta-mediated signal delivery from the TCR/CD28 surface receptors

Protein kinase C-theta (PKCθ) is a key enzyme in T lymphocytes, where it plays an important role in signal transduction downstream of the activated T cell antigen receptor (TCR) and the CD28 costimulatory receptor. Interest in PKCθ as a potential drug target has increased following recent findings that PKCθ is essential for harmful inflammatory responses mediated by Th2 (allergies) and Th17 (autoimmunity) cells as well as for graft-versus-host disease (GvHD) and allograft rejection, but is dispensable for beneficial responses such as antiviral immunity and graft-versus-leukemia (GvL) response. TCR/CD28 engagement triggers the translocation of the cytosolic PKCθ to the plasma membrane (PM), where it localizes at the center of the immunological synapse (IS), which forms at the contact site between an antigen-specific T cell and antigen-presenting cells (APC). However, the molecular basis for this unique localization, and whether it is required for its proper function have remained unresolved issues until recently. Our recent study resolved these questions by demonstrating that the unique V3 (hinge) domain of PKCθ and, more specifically, a proline-rich motif within this domain, is essential and sufficient for its localization at the IS, where it is anchored to the cytoplasmic tail of CD28 via an indirect mechanism involving Lck protein tyrosine kinase (PTK) as an intermediate. Importantly, the association of PKCθ with CD28 is essential not only for IS localization, but also for PKCθ-mediated activation of downstream signaling pathways, including the transcription factors NF-κB and NF-AT, which are essential for productive T cell activation. Hence, interference with formation of the PKCθ-Lck-CD28 complex provides a promising basis for the design of novel, clinically useful allosteric PKCθ inhibitors. An additional recent study demonstrated that TCR triggering activates the germinal center kinase (GSK)-like kinase (GLK) and induces its association with the SLP-76 adaptor at the IS, where GLK phosphorylates the activation loop of PKCθ, converting it into an active enzyme. This recent progress, coupled with the need to study the biology of PKCθ in human T cells, is likely to facilitate the development of PKCθ-based therapeutic modalities for T cell-mediated diseases.

Bronchoprovocation testing in asthma

This article covers the relationships between BHR and airway inflammation. Recent evidence suggests that various commonly used bronchoprovocation challenges (BPCs) differ in their potential to serve as inflammatory biomarkers. The response to direct stimuli depends on the smooth muscle's response to the chemical, whereas in indirect challenges, the reaction is caused by the smooth muscle's responsiveness to the mediators induced by the stimuli. The information obtained from studies with BPC has provided insights into the pathogenesis and pathophysiology of asthma, and the relationships between airway inflammation and bronchial hyper-responsiveness.

Prevention of house dust mite induced allergic airways disease in mice through immune tolerance

Allergic airways disease is a consequence of a Th2 response to an allergen leading to a series of manifestations such as production of allergen-specific IgE, inflammatory infiltrates in the airways, and airway hyper-reactivity (AHR). Several strategies have been reported for tolerance induction to allergens leading to protection from allergic airways disease. We now show that CD4 blockade at the time of house dust mite sensitization induces antigen-specific tolerance in mice. Tolerance induction is robust enough to be effective in pre-sensitized animals, even in those where AHR was pre-established. Tolerant mice are protected from airways eosinophilia, Th2 lung infiltration, and AHR. Furthermore, anti-CD4 treated mice remain immune competent to mount immune responses, including Th2, to unrelated antigens. Our findings, therefore, describe a strategy for tolerance induction potentially applicable to other immunogenic proteins besides allergens.

Intrinsic and extrinsic control of peripheral T-cell tolerance by costimulatory molecules of the CD28/ B7 family

Positive and negative costimulation by members of the CD28 family is critical for the development of productive immune responses against foreign pathogens and their proper termination to prevent inflammation-induced tissue damage. In addition, costimulatory signals are critical for the establishment and maintenance of peripheral tolerance. This paradigm has been established in many animal models and has led to the development of immunotherapies targeting costimulation pathways for the treatment of cancer, autoimmune disease, and allograft rejection. During the last decade, the complexity of the biology of costimulatory pathways has greatly increased due to the realization that costimulation does not affect only effector T cells but also influences regulatory T cells and antigen-presenting cells. Thus, costimulation controls T-cell tolerance through both intrinsic and extrinsic pathways. In this review, we discuss the influence of costimulation on intrinsic and extrinsic pathways of peripheral tolerance, with emphasis on members of the CD28 family, CD28, cytotoxic T-lymphocyte antigen-4 (CTLA-4), and programmed death-1 (PD-1), as well as the downstream cytokine interleukin-1 (IL-2).

BTNL2 gene polymorphisms may be associated with susceptibility to Kawasaki disease and formation of coronary artery lesions in Taiwanese children

The butyrophilin-like 2 (BTNL2) gene is a member of the B7 receptor family that probably functions as a T cell costimulatory molecule. Because altered T cell functions are implicated in dysregulation of the immune response seen in Kawasaki disease (KD), it is reasonable to speculate that BTNL2 gene is involved in the pathophysiology of KD. The purpose of this study was to investigate whether polymorphisms of the BTNL2 gene are associated with KD and the development of coronary artery lesions (CALs) in Taiwanese children. Nine-three patients with KD and 669 ethnically matched healthy controls were genotyped for BTNL2 gene rs1555115 C/G and rs2395158 A/G polymorphisms. The frequency of GG genotype of rs 1555115 was significantly higher in KD patients compared with controls (2.2% vs 0.2%, P = 0.012). The odds ratio for developing KD in individuals with rs 1555115 GG genotype was 14.7 (95% confidence interval, 2.04-105.5, P = 0.003) compared with individuals with rs 1555115 CG and CC genotypes. No significant difference was observed in the genotype and allelic frequencies of rs 2395158 polymorphism between KD patients and controls. However, the frequency of the G allele of rs 2395158 was significantly higher in KD patients with CALs than in those without CALs (P = 0.001). No significant difference was observed in the genotype and allelic frequencies of rs 1555115 polymorphism between KD patients with and without CALs. In conclusion, our results suggest that BTNL2 gene polymorphisms might be genetic markers of KD susceptibility and risk of coronary artery complication in Taiwanese children.

Association and interaction analyses of eight genes under asthma linkage peaks

BACKGROUND

Linkage studies have implicated the 2q33, 9p21, 11q13 and 20q13 regions in the regulation of allergic disease. The aim of this study was to test genetic variants in candidate genes from these regions for association with specific asthma traits.

METHODS

Ninety-five single nucleotide polymorphisms (SNP) located in eight genes (CD28, CTLA4, ICOS, ADAM23, ADAMTSL1, MS4A2, CDH26 and HRH3) were genotyped in >5000 individuals from Australian (n = 1162), Dutch (n = 99) and Danish (n = 303) families. Traits tested included doctor-diagnosed asthma, atopy, airway obstruction, total serum immunoglobulin (Ig) E levels and eosinophilia. Association was tested using both multivariate and univariate methods, with gene-wide thresholds for significance determined through simulation. Gene-by-gene and gene-by-environment analyses were also performed.

RESULTS

There was no overall evidence for association with seven of the eight genes tested when considering all genetic variation assayed in each gene. The exception was MS4A2 on chromosome 11q13, which showed weak evidence for association with IgE (gene-wide P < 0.05, rs502581). There were no significant gene-by-gene or gene-by-environment interaction effects after accounting for the number of tests performed.

CONCLUSIONS

The individual variants genotyped in the 2q33, 9p21 and 20q13 regions do not explain a large fraction of the variation in the quantitative traits tested or have a major impact on asthma or atopy risk. Our results are consistent with a weak effect of MS4A2 polymorphisms on the variation of total IgE levels.

Airway cytokine responses to acute and repeated stress in a murine model of allergic asthma

Although stress is known to exacerbate asthma, the underlying mechanisms are unclear. Using a murine model of allergic asthma, Th1 (interleukin [IL]-2 and gamma-interferon [IFN-γ]) and Th2 (IL-4 and IL-5) airway cytokine responses and Th1:Th2 cytokine ratios to acute and repeated stress were examined in bronchoalveolar lavage fluid (BALF). Asthmatic mice showed significantly higher IL-4 level and Th2 predominance, compared with healthy mice. To acute stress, asthmatic mice significantly increased IL-4 but decreased IFN-γ levels favoring Th2 predominance, whereas healthy mice significantly decreased IL-4 level favoring Th1 predominance in BALF. To repeated stress, asthmatic mice significantly decreased IFN-γ, IL-4 and IL-5 levels overall favoring Th1 predominance, whereas healthy mice basically maintained the same response profile shown to acute stress. These findings suggest that a significant shift toward Th2 predominance in asthmatic mice under acute stress may be a mechanism underlying exacerbation of asthma.

CD28 and ICOS play complementary non-overlapping roles in the development of Th2 immunity in vivo

Previous work has shown ICOS can function independently of CD28, but whether either molecule can compensate for the other in vivo is not known. Since ICOS is a potent inducer of Th2 cytokines and linked to allergy and elevated serum IgE in humans, we hypothesized that augmenting ICOS costimulation in murine allergic airway disease may overcome CD28 deficiency. While ICOS was expressed on T cells from CD28(-/-) mice, Th2-mediated airway inflammation was not induced in CD28(-/-) mice by increased ICOS costimulation. Further, we determined if augmenting CD28 costimulation could compensate for ICOS deficiency. ICOS(-/-) mice had a defect in airway eosinophilia that was not overcome by augmenting CD28 costimulation. CD28 costimulation also did not fully compensate for ICOS for antibody responses, germinal center formation or the development of follicular B helper T cells. CD28 and ICOS play complementary non-overlapping roles in the development of Th2 immunity in vivo.

B7-H3 contributes to the development of pathogenic Th2 cells in a murine model of asthma

B7-H3 is a new member of the B7 family. The receptor for B7-H3 has not been identified, but it seems to be expressed on activated T cells. Initial studies have shown that B7-H3 provides a stimulatory signal to T cells. However, recent studies suggest a negative regulatory role for B7-H3 in T cell responses. Thus, the immunological function of B7-H3 is controversial and unclear. In this study, we investigated the effects of neutralizing anti-B7-H3 mAb in a mouse model of allergic asthma to determine whether B7-H3 contributes to the development of pathogenic Th2 cells and pulmonary inflammation. Administration of anti-B7-H3 mAb significantly reduced airway hyperreactivity with a concomitant decrease in eosinophils in the lung as compared with control IgG-treated mice. Treatment with anti-B7-H3 mAb also resulted in decreased production of Th2 cytokines (IL-4, IL-5, and IL-13) in the draining lymph node cells. Although blockade of B7-H3 during the induction phase abrogated the development of asthmatic responses, B7-H3 blockade during the effector phase did not inhibit asthmatic responses. These results indicated an important role for B7-H3 in the development of pathogenic Th2 cells during the induction phase in a murine model of asthma.

Costimulation blockade in autoimmunity and transplantation

Signaling through the costimulation receptors is a critical pathway in the regulation of T-cell activation. The selective costimulation inhibitor abatacept (cytotoxic T lymphocyte-associated antigen 4-Ig) binds to CD80 and CD86 on antigen-presenting cells, blocking interaction with CD28 on T cells, and is approved for the treatment of moderate to severe rheumatoid arthritis. Belatacept (LEA29Y), currently enrolling phase III trials in renal transplantation, was rationally designed from abatacept to bind with more avidity to CD86, providing the more potent immunosuppressive properties required for immunosuppression in transplantation. This review describes the relevant preclinical studies and summarizes recent clinical findings on these 2 molecules in autoimmune diseases and organ transplantation. Although both inhibit the CD28 costimulatory pathway, they are tailored for specific disease states--abatacept for autoimmune diseases and belatacept for transplantation.

The future of asthma therapy: integrating clinical and experimental studies

Asthma is one of the most common, and now most heavily investigated, of modern diseases. Research along two fronts, involving experimental models of asthma and human clinical trials, proceeds in parallel, often with investigators unaware of their counterpart's findings. Here, we review the unique immunological insights into asthma pathogenesis and therapy that may be gained from comparison of human clinical trial results and analogous experimental studies. The pitfalls and benefits of animal models of asthma are discussed, and we briefly review ongoing asthma clinical studies that are based on immunological principals. Finally, we use new insights from human and animal studies to construct a refined immunopathologic disease model that may be of use in designing future experimental and therapeutic studies.

Bronchoprovocation testing in asthma

Bronchial hyperresponsiveness (BHR) is an important feature of asthma and is useful in diagnosis, monitoring, and prognostication. It probably represents inherent elements of the disease process such as genetic predisposition, airway inflammation, and airway remodeling. Airway inflammation likely accounts for the variable component of BHR, whereas the persistent component of BHR correlates significantly with structural changes in the airway, such as basement membrane thickness and epithelial damage. It might be this component that is resistant or refractory to the effects of available interventions. A few trials of immunomodulatory therapy have shown considerable improvements in markers of airway inflammation, without significantly modifying airway reactivity. Interventions to impact the more permanent feature of BHR are needed.

(R)-albuterol decreases immune responses: role of activated T cells

Racemic albuterol is an equimolar mixture of two isomers, (R) and (S). Whether (R) and (S) isomers and the combination of both exert different effects in immune activation is not well defined. We analyzed the effects of (R+S)-albuterol, (R)-albuterol and (S)-albuterol in a murine model of allergic pulmonary inflammation and in activated T cells. Mice (C57BL/6) sensitized and aerosol challenged with the allergen ovalbumin (OVA) or phosphate buffered saline (PBS) were treated with (R)-albuterol, (S)-albuterol or (R+S)-albuterol. Following administration of (R)-albuterol, allergen induced bronchoalveolar lavage eosinophils and IgE showed a decrease, albeit not significantly by ANOVA. As T cells are important in allergic inflammation, we asked whether (R+S), (R) or (S)-albuterol might differ in effects on T cells and on the activity of the inflammatory transcription factor NF-κB. In activated T cells, (R)-albuterol administration decreased levels of inflammatory cytokines and NF-κB activity. These studies suggest that (R)-albuterol decreases cytokine secretion and NF-κB activity in T cells.

Costimulation and allergic responses: immune and bioinformatic analyses

Asthma is a complex polygenic disease, the prevalence of which has been on the rise for last few decades. Defining the underpinnings of allergic immune responses and the factors predisposing to asthma are fundamental investigative challenges. T cell costimulatory pathways play critical roles in the pathogenesis of asthma. In this review, we analyze the current state of the art of T cell costimulation in allergic airway inflammation. Also, we discuss both immune and bioinformatic approaches as potential strategies for analyzing multiple costimulatory pathways relevant to asthma.

CD45RB ligation inhibits allergic pulmonary inflammation by inducing CTLA4 transcription

CD45, a type I transmembrane protein tyrosine phosphatase expressed on nucleated hemopoietic cells, is prominently involved in T cell activation. Ligation of CD45RB isoforms has been associated with transplant tolerance. A recent genotyping analysis of asthma indicates a correlation with CD45 splicing. In this study, we administered an anti-CD45RB mAb (aCD45) in a murine model of allergic asthma and found that CD45RB ligation decreases allergic responses. aCD45 decreases allergen-induced pulmonary eosinophilia, bronchoalveolar lavage IL-13, IgE, and airway responses. Also, aCD45 increases the expression of CTLA4, a negative regulator of T cell activation. Furthermore, CD45RB signals no longer decrease allergic inflammation when CTLA4 is inhibited. These data support a role for CTLA4 in CD45RB-mediated inhibition of allergic inflammation. T cells and splenocytes stimulated with aCD45 exhibited increased CTLA4 levels, and analysis of CTLA4 promoter gene constructs identified a CD45RB-inducible regulatory region localized from -335 to -62 bp relative to the transcription start site. Together, these findings suggest that CD45RB signals mediate a novel role in the modulation of allergic inflammation, orchestrated by T cells through induction of CTLA4 transcription.

Costimulation blockade inhibits allergic sensitization but does not affect established allergy in a murine model of grass pollen allergy

Type I allergy is characterized by the development of an initial Th2-dependent allergen-specific IgE response, which is boosted upon a subsequent allergen encounter. Although the immediate symptoms of allergy are mainly IgE-mediated, allergen-specific T cell responses contribute to the late phase as well as to the chronic manifestations of allergy. This study investigates the potential of costimulation blockade with CTLA4Ig and an anti-CD154 mAb for modifying the allergic immune response to the major timothy grass pollen allergen Phl p 5 in a mouse model. BALB/c mice were treated with the costimulation blockers at the time of primary sensitization to the Phl p 5 allergen or at the time of a secondary allergen challenge. Costimulation blockade (CTLA4Ig plus anti-CD154 or anti-CD154 alone) at the time of sensitization prevented the development of allergen-specific IgE, IgM, IgG, and IgA responses compared with untreated but sensitized mice. However, costimulation blockade had no influence on established IgE responses in sensitized mice. Immediate-type reactions as analyzed by a rat basophil leukemia cell mediator release assay were only suppressed by early treatment but not by a costimulation blockade after sensitization. CTLA4Ig given alone failed to suppress both the primary and the secondary allergen-specific Ab responses. Allergen-specific T cell activation was suppressed in mice by early as well as by a late costimulation blockade, suggesting that IgE responses in sensitized mice are independent of T cell help. Our results indicate that T cell suppression alone without active immune regulation or a shifting of the Th2/Th1 balance is not sufficient for the treatment of established IgE responses in an allergy.

Inhaled CD86 antisense oligonucleotide suppresses pulmonary inflammation and airway hyper-responsiveness in allergic mice

The B7-family molecule CD86, expressed on the surface of pulmonary and thoracic lymph node antigen-presenting cells, delivers essential costimulatory signals for T-cell activation in response to inhaled allergens. CD86-CD28 signaling is involved in priming allergen-specific T cells, but it is unclear whether these interactions play a role in coordinating memory T-helper 2 cell responses. In the ovalbumin (OVA)-induced mouse model of asthma, administration of CD86-specific antibody before systemic sensitization suppresses inhaled OVA-induced pulmonary inflammation and airway hyper-responsiveness (AHR). In previously OVA-sensitized mice, systemic and intranasal coadministration of CD86 antibody is required to produce these effects. To directly assess the importance of pulmonary CD86 expression in secondary immune responses to inhaled allergens, mice were sensitized and locally challenged with nebulized OVA before treatment with an inhaled aerosolized CD86 antisense oligonucleotide (ASO). CD86 ASO treatment suppressed OVA-induced up-regulation of CD86 protein expression on pulmonary dendritic cells and macrophages as well as on recruited eosinophils. Suppression of CD86 protein expression correlated with decreased methacholine-induced AHR, airway inflammation, and mucus production following rechallenge with inhaled OVA. CD86 ASO treatment reduced BAL eotaxin levels, but it did not reduce CD86 protein on cells in the draining lymph nodes of the lung, and it had no effect on serum IgE levels, suggesting a local and not a systemic effect. These results demonstrate that CD86 expression on pulmonary antigen-presenting cells plays a vital role in regulating pulmonary secondary immune responses and suggest that treatment with an inhaled CD86 ASO may have utility in asthma and other chronic inflammatory lung conditions.

CD48 is critically involved in allergic eosinophilic airway inflammation

RATIONALE

Despite ongoing research, the molecular mechanisms controlling asthma are still elusive. CD48 is a glycosylphosphatidylinositol-anchored protein involved in lymphocyte adhesion, activation, and costimulation. Although CD48 is widely expressed on hematopoietic cells and commonly studied in the context of natural killer and cytotoxic T cell functions, its role in helper T cell type 2 settings has not been examined.

OBJECTIVES

To evaluate the expression and function of CD48, CD2, and 2B4 in a murine model of allergic eosinophilic airway inflammation.

METHODS

Allergic eosinophilic airway inflammation was induced by ovalbumin (OVA)-alum sensitization and intranasal inoculation of OVA or, alternatively, by repeated intranasal inoculation of Aspergillus fumigatus antigen in wild-type, STAT (signal transducer and activator of transcription)-6-deficient, and IL-4/IL-13-deficient BALB/c mice. Gene profiling of whole lungs was performed, followed by Northern blot and flow cytometric analysis. Anti-CD48, -CD2, and -2B4 antibodies were administered before OVA challenge and cytokine expression and histology were assessed.

MEASUREMENTS AND MAIN RESULTS

Microarray data analysis demonstrated upregulation of CD48 in the lungs of OVA-challenged mice. Allergen-induced CD48 expression was independent of STAT-6, IL-13, and IL-4. Neutralization of CD48 in allergen-challenged mice abrogated bronchoalveolar lavage fluid and lung inflammation. Neutralization of CD2 inhibited the inflammatory response to a lesser extent and neutralization of 2B4 had no effect.

CONCLUSIONS

Our results suggest that CD48 is critically involved in allergic eosinophilic airway inflammation. As such, CD48 may provide a new potential target for the suppression of asthma.

A negative regulatory role in mouse cardiac transplantation for a splice variant of CD80

BACKGROUND

Members of the B7 costimulatory protein family (CD80 and CD86) play a determining role in allograft rejection. Both CD80 and CD86 have naturally occurring splice variants whose roles in transplantation are unknown. Full length CD80 has two immunoglobulin (Ig)-like domains in the extracellular portion, IgC and IgV. In mouse, the isoform IgV-CD80 lacks the IgC-like domain. Here we analyzed the role of mouse IgV-CD80 in heart allograft rejection and search for equivalent splice variants in human.

METHODS

Mice made deficient for full-length CD80 but which retain expression of the shorter IgV-CD80 (CD80 mice) were used as donor or recipient of a heart allograft. Recipient animals were untreated or pretreated with alloantigen expressing cells and/or treated with CD80 and CTLA4 monoclonal antibodies (mAbs).

RESULTS

Recipients expressing IgV-CD80 but not full length CD80 exhibited a slight prolongation in survival of either wild-type (Wt) or CD80 grafts. More dramatically, CD80 animals pretreated with donor alloantigen exhibited permanent graft survival, whereas their Wt counterparts rejected their grafts with a median survival of 24 days. This prolonged survival was due to the expression of IgV-CD80 in recipients since treatment with CD80 mAb abrogated the beneficial effect observed. We identified and report here a similar isoform of CD80 from human cDNA encoding a putative soluble, IgV-containing protein.

CONCLUSIONS

IgV-CD80 bearing recipients show enhanced allograft survival especially after donor alloantigen pretreatment. This together with data from other species suggests that regulation delivered by splice variants of CD80 significantly modulates immunity and may be common across the species.

Differential contributions of B7-1 and B7-2 to the development of murine experimental allergic conjunctivitis

B7-1 and B7-2 are the co-stimulatory molecules that are involved in activation of T cells. We investigated whether B7-1 and B7-2 play a role in the development of T cell-mediated experimental allergic conjunctivitis (EC). EC was induced in Balb/c mice by active immunization with ragweed (RW) followed by RW challenge in eye drops. These mice were treated with neutralizing anti-B7-1 Ab, anti-B7-2 Ab, both Abs, anti-cytotoxic T lymphocyte-associated Ag-4 (CTLA-4) Ab or normal IgGs as controls either during the induction phase or the effector phase. With regard to the induction phase treatment, EC was significantly attenuated when both anti-B7-1 and anti-B7-2 Abs were injected. In contrast, anti-CTLA-4 Ab treatment significantly exacerbated EC. With regard to the effector phase treatment, anti-B7-2 Ab alone significantly attenuated EC, while anti-CTLA-4 Ab tended to exacerbate EC. Collectively, B7-1 and B7-2 differently contribute to the development of EC during the induction and effector phases.

IgE-mediated allergen presentation and blocking antibodies: regulation of T-cell activation in allergy

It is well established that both the production of IgE by B lymphocytes and the maturation and recruitment of eosinophils in late-phase reactions are dependent on the activation of allergen-specific type-2 T-helper cells. What is less well known is the fact that efficient activation of allergen-specific T cells upon low-dose exposure to allergens is critically dependent on IgE-mediated or -facilitated allergen presentation. In fact, changes in the level of IgE-mediated allergen presentation may account for many of the immunological effects described for specific immunotherapy or anti-IgE treatment. This review aims to summarize the current knowledge, and will discuss the clinical relevance of blocking IgG antibodies induced by specific immunotherapy and anti-IgE monoclonal antibodies that both interfere with IgE-mediated allergen presentation.

Molecular regulation of cytoskeletal rearrangements during T cell signalling

Regulation of the cytoskeleton in cells of the haematopoietic system is essential for fulfilling diverse tasks such as migration towards a chemoattractant, phagocytosis or cell-cell communication. This is particularly true for the many types of T cells, which are at the foundation of the adaptive immune system in vertebrates. Deregulation of actin filament turnover is known to be involved in the development of severe immunodeficiencies or immunoproliferative diseases. Therefore, molecular dissection of signalling complexes and effector molecules, which leads to controlled cytoskeletal assembly, has been the focus of immunological research in the last decade. In the past, cytoskeletal remodelling was frequently understood as the finish line of signalling, while today it becomes increasingly evident that actin and microtubule dynamics are required for proper signal transmission in many processes such as T cell activation. Significant effort is made in many laboratories to further elucidate the contribution of cytoskeletal remodelling to immune function. The objective of this article is to summarise the current knowledge on how actin and microtubules are reorganised to support the formation of structures as diverse as the immunological synapse and peripheral protrusions during cell migration.

Co-stimulatory molecules as potential targets for therapeutic intervention in allergic airway disease

Airway inflammation is a characteristic feature of allergic asthma. Central to the initiation and progression of the inflammatory process are allergen-specific T lymphocytes that attract eosinophils, mast cells, and B cells to the airways by the secretion of specific cytokines. The direction of T cell responses is influenced by co-stimulatory signals that modulate the antigen-specific signal delivered by the T cell receptor. In addition to the prototypic co-stimulatory molecule, CD28, a number of newly identified co-stimulatory molecules and their ligands have now been characterized. Over the past 5 years, the role of these molecules in the pathophysiology of allergen-mediated sensitization and airway inflammation has been extensively studied in animal models of allergic asthma. The aim of this review is to provide a detailed overview on recent studies in mice and preliminary findings in man and to discuss the potential therapeutic and preventive treatment strategies offered by interactions with co-stimulatory molecules for patients with allergic airway diseases.

The costimulatory molecule SLAM is critical for pulmonary allergic responses

T-cell activation plays an essential role in the generation of the pulmonary inflammation that is manifest in allergic asthma. Optimal T-cell activation requires not only presentation of antigen with the major histocompatibility complex, but also concurrent signaling through costimulatory molecules. The costimulatory molecule SLAM (Signaling Lymphocytic Activation Molecule, CD150) is a glycoprotein expressed on activated lymphocytes and antigen-presenting cells. Disruption of the SLAM gene demonstrated that SLAM-induced signal transduction pathways regulate cytokine production by T helper (Th)2 cells and macrophages. Here we tested the postulate that the costimulatory molecule SLAM may be critical for allergic inflammation in a murine model. SLAM-deficient mice did not manifest allergen-induced bronchoalveolar lavage eosinophilia, increased serum IgE, or heightened airway responses compared with wild-type mice. Allergen-induced Th2 cytokines and Th1 cytokines were decreased in SLAM-deficient mice. These data support the concept that SLAM plays a crucial role in allergic responses.

Blockade of CTLA-4 promotes airway inflammation in naive mice exposed to aerosolized allergen but fails to prevent inhalation tolerance

In subjects not developing allergy, inhalation of nonpathogenic protein antigens causes no harm and is associated with tolerance induction. Repeated exposure to aerosolized ovalbumin (OVA) likewise does not evoke airway inflammation and induces inhalation tolerance in experimental animals. The present study explored the role of the inhibitory T-cell receptor CTLA-4, in preventing inflammation and in establishing inhalation tolerance in response to a protein antigen. Naive BALB/c mice were injected intraperitoneally with anti-CTLA-4 monoclonal antibody or control immunoglobulin G (IgG) and exposed daily to aerosolized saline or OVA over 10 or 20 consecutive days. OVA-specific IgE levels and the inflammatory response in airway tissues were assessed 2 days after last exposure. The OVA-specific IgE response was also evaluated in mice subjected to a subsequent immunogenic OVA challenge 18 days after last aerosol exposure. Additional mice were made tolerant by 10 days of OVA aerosol exposure and were then subjected to an immunogenic OVA challenge combined with CTLA-4 blockade or control IgG treatment. Repeated inhalation of aerosolized OVA alone did not cause a pulmonary inflammatory response. In contrast, 10 days of OVA exposure combined with blockade of CTLA-4 led to development of eosinophilic lung infiltrates, BAL fluid eosinophilia, goblet cell hyperplasia and increased OVA-specific IgE. By 20 days of OVA exposure and blockade of CTLA-4, the inflammatory response remained. Mice exposed to aerosolized OVA for 10 days exhibited greatly reduced OVA-specific IgE responses to subsequent immunogenic OVA challenge. Blockade of CTLA-4 during the period of OVA aerosol exposure did not prevent this suppression of the OVA-specific IgE response. Neither did blockade of CTLA-4 during immunogenic OVA challenge alter the allergen-specific IgE response. Our results indicate that in vivo blockade of CTLA-4 modulates the initial immune response to a protein antigen allowing the development of allergen-induced airway inflammation in naive mice. However, this initial exaggerated immune response is followed by the induction of inhalation tolerance, demonstrating that CTLA-4 signalling is not decisive in this process. Our findings also show that once inhalation tolerance is established it may not be disrupted by blockade of CTLA-4.

The costimulatory molecules CD80, CD86 and OX40L are up-regulated in Aspergillus fumigatus sensitized mice

Aspergillus fumigatus (Af) is a fungus associated with allergic bronchopulmonary aspergillosis (ABPA) and other allergic diseases. Immune responses in these diseases are due to T and B cell responses. T cell activation requires both Af-specific engagement of the T-cell-receptor as well as interaction of antigen independent costimulatory molecules including CD28-CD80/CD86 and OX40-OX40L interactions. Since these molecules and their interactions have been suggested to have a potential involvement in the pathogenesis of ABPA, we have investigated their role in a model of experimental allergic aspergillosis. BALB/c mice were primed and sensitized with Af allergens, with or without exogenous IL-4. Results showed up-regulation of both CD86 and CD80 molecules on lung B cells from Af-sensitized mice (79% CD86+ and 24% CD80+) and Af/rIL-4-treated mice (90% CD86+ and 24% CD80+) compared to normal controls (36% and 17%, respectively). Lung macrophages in Af-sensitized mice treated or not with IL-4 showed enhanced expression of these molecules. OX40L expression was also up-regulated on lung B cells and macrophages from both Af-sensitized and Af/rIL-4 exposed mice as compared to normal controls. All Af-sensitized animals showed peripheral blood eosinophilia, enhanced total serum IgE and allergen-specific IgG1 antibodies and characteristic lung inflammation. The up-regulation of CD80, CD86 and OX40L molecules on lung B cells and macrophages from Af-allergen exposed mice suggests a major role for these molecules in the amplification and persistence of immunological and inflammatory responses in ABPA.

The BTNL2 gene and sarcoidosis susceptibility in African Americans and Whites

The BTNL2 gene is a member of the B7 receptor family that probably functions as a T-cell costimulatory molecule. It resides in the class II major histocompatibility complex (MHC) region of chromosome 6p and has recently been associated with sarcoidosis susceptibility in a white German population. We sought to replicate the BTNL2 association in an African American family-based study population (n=219 nuclear families) and two case-control populations--one African American (n=295 pairs) and one white (n=366 pairs). Ten SNPs were detected within a 490-bp region spanning exon/intron 5 of BTNL2. Haplotype variation within this region was significantly associated with sarcoidosis in all three study populations but more so in whites (P=.0006) than in the African American case-control (P=.02) or family-based (P=.03) samples. The previously reported BTNL2 SNP with the strongest sarcoidosis association, rs2076530, was also the SNP with the strongest association in our white population (P<.0001). The A allele of rs2076530 results in a premature exon-splice site and increases risk for sarcoidosis (odds ratio=2.03; 95% confidence interval 1.32-3.12). Although rs2076530 was not associated with sarcoidosis in either African American sample, a three-locus haplotype that included rs2076530 was associated with sarcoidosis across all three study samples. Multivariable logistic regression analyses showed that BTNL2 effects are independent of human leukocyte antigen class II genes in whites but may interact antagonistically in African Americans. Our results underscore the complexity of genetic risk for sarcoidosis emanating from the MHC region.

Costimulation: critical pathways in the immunologic regulation of asthma

T cells play an important role in the pathogenesis of allergy and asthma. T-cell receptor engagement by antigenic peptides presented to major histocompatibility complex (MHC) class II molecules and activation of costimulatory molecules are crucial in the regulation of T-cell immune responses. Costimulatory molecules are responsible for second signals that induce T-cell activation and proliferation. The best characterized costimulatory pathways include CD80/CD86 interacting with CD28, and a number of additional costimulatory molecules have recently been identified, including members of the tumor necrosis family. The positive signals induced by these molecules are counterbalanced by other members of the costimulatory family, including cytotoxic T lymphocyte-associated antigen (CTLA)-4, programmed death (PD)-1, and B and T lymphocyte attenuator (BTLA), which dampen immune responses. In this review, we describe the fundamental properties of costimulatory molecules and address the influence of costimulatory signals on allergic responses.

Effects of allergen inhalation and oral glucocorticoid on serum soluble CTLA-4 in allergic asthmatics

BACKGROUND

The serum soluble cytotoxic T lymphocyte associated antigen-4 (sCTLA-4) concentration is significantly elevated in patients with asthma, and sCTLA-4 concentration correlate with the severity of asthma. The aim of the present study was to investigate effects of allergen inhalation and oral glucocorticoid on concentration of serum sCTLA-4 in patients with allergic asthma.

METHODS

Allergen inhalation challenge was conducted in allergic asthmatics with isolated early asthma response and those with dual asthma response. In a randomized, double-blind, placebo-controlled, parallel group fashion, prednisolone or placebo was give orally once a day for 2 weeks. Venous blood samples were collected before and after allergen inhalation or prednisolone administration for obtaining sera. The serum sCTLA-4 concentrations were determined using enzyme-linked immunosorbent assay.

RESULTS

The serum sCTLA-4 concentrations in the dual responder group increased from 29.0 (14.5-43.7) microg/l [median (25-75 percentiles)] before allergen inhalation to 44.0 (24.3-61.3) microg/l 24 h after allergen inhalation. In the isolated early responders, there were no significant increase in serum sCTLA-4 concentrations after allergen inhalation compared with baseline levels. There was a significant decrease in serum sCTLA-4 concentrations after 2 weeks of glucocorticoid therapy [22.0 (15.5-31.0) microg/l] compared with baseline values [37.0 (19.5-53.0) microg/l], whereas there was no significant difference in the placebo group.

CONCLUSION

This study has demonstrated that serum sCTLA-4 concentrations increased after allergen inhalation in sensitized asthmatic subjects, and that serum sCTLA-4 concentrations were downregulated by prednisolone therapy.

T cells modulate neutrophil-dependent acute renal failure during endotoxemia: critical role for CD28

Sepsis still represents a leading cause of acute renal failure (ARF). Both lymphocytes and neutrophils (PMN) have been proposed as crucial mediators during sepsis. For further elucidation of the mechanisms of interactions between them, a murine model of LPS-induced ARF was used. In wild-type mice (WT), LPS administration led to a strong influx of PMN into the kidney (2.8-fold greater renal myeloperoxidase activity after 24 h) and to severe ARF (3.3-fold higher plasma creatinine concentrations after 24 h). By contrast, mice that were gene deficient for CD28 (CD28(-/-)), a co-stimulatory molecule for T cell activation, exhibited only minor renal dysfunction (50% protection compared with WT) and almost no PMN recruitment. When PMN(-) depleted, both WT and CD28(-/-) developed only mild ARF, similar to untreated CD28(-/-). Flow cytometry demonstrated that CD28 was vastly expressed on CD3(+) cells but not on PMN. Injecting wild-type CD3(+) cells into CD28(-/-) before LPS injection abolished the protection seen before. At baseline, both WT and CD28(-/-) displayed similar plasma concentrations of keratinocyte-derived chemokine (KC), a growth-related oncogene 1 gene product and PMN-specific chemokine. As opposed to WT, CD28(-/-) showed a greatly attenuated increase in plasma KC 4 h after LPS (2.5- versus 138.5-fold over controls, respectively). Moreover, CD28(-/-) showed less intense upregulation of renal growth-related oncogene 1 mRNA expression. Immunohistochemistry revealed considerable PMN but no T cell infiltrates in the kidney after LPS injection. In a PMN-dependent model of endotoxemic ARF, T cells, via the CD28 pathway, modulate kidney function and renal PMN recruitment. The effect on PMN is a remote one and presumably due to altered expression of PMN-specific chemokines.

Toll-like receptor 4 or 2 agonists decrease allergic inflammation

Toll-like receptors (TLRs) recognize highly conserved microbial molecular patterns, such as found in endotoxin. This study tested whether TLR4 and TLR2 stimulation in vivo would modulate subsequent adaptive (allergic) immune responses. We analyzed the effects of pulmonary administration of a TLR4 agonist, lipid A (LpA), and two TLR2 agonists, peptidoglycan (Ppg) and PamCys, in a murine model of allergic inflammation. The TLR agonists were administered during allergen sensitization or challenge. Both TLR agonists decreased the allergen-induced pulmonary recruitment of eosinophils when administered at sensitization or challenge. When given before sensitization, the TLR4 and TLR2 agonists decreased additional allergen-induced parameters of inflammation (pulmonary eosinophilia, bronchoalveolar lavage IL-13, total serum IgE, and airway hyperresponsiveness). Interestingly, TLR4 and TLR2 agonists decreased the number of CD4+ cells in the lung. Also, at the site of local allergen stimulation, the draining thoracic lymph nodes, allergen-induced lymphocyte proliferation, and IL-13 secretion were decreased by administration of LpA and Ppg. These data provide a distinct example of the modulation of adaptive (allergic) responses by non-antigen-dependent stimuli. Our findings also demonstrate that both TLR4 and TLR2 agonists decrease allergic responses, supporting the concept that exposure to bacterial components under defined conditions may protect against allergic disease.

Soluble CD86 protein in serum samples of patients with asthma

BACKGROUND

Previous studies have reported that soluble (s) CD86 is involved in the initiation of the immune response. A study was undertaken to investigate the concentrations of sCD86 in serum samples from patients with bronchial asthma and to determine the cell origin of sCD86.

METHODS

Serum sCD86 concentrations were measured in 52 asthmatic subjects and 25 non-atopic normal volunteers using an enzyme linked immunosorbent assay, and the relationship of serum sCD86 concentrations to asthma severity and to total and differential white cell counts was analysed. Each type of white blood cell was purified and cultured in vitro to determine the cell origin of serum sCD86.

RESULTS

Serum samples from patients with an acute asthma exacerbation had much higher levels of sCD86 (585.4 (20.5) IU/ml) than those from stable asthmatics (479.6 (15.7) IU/ml, p<0.001) and healthy individuals (435.1 (13.8) IU/ml, p<0.001), and there was no difference between the latter two groups (p = 0.079). In asthmatic subjects the serum sCD86 level was inversely correlated with airway responsiveness, forced expiratory volume in 1 second, and with arterial carbon dioxide tension. In addition, the serum sCD86 level was positively correlated with numbers of lymphocytes, eosinophils, monocytes, but not neutrophils. The in vitro experiments indicated that sCD86 was produced by monocytes.

CONCLUSIONS

The serum sCD86 protein level was significantly increased in asthmatic subjects during an exacerbation and correlated with the severity of asthma. sCD86 is most probably derived from monocytes in the peripheral blood.

Requirement for CD28 in the effector phase of allergic airway inflammation

Central to the pathogenesis of allergic airway inflammation are the activation and differentiation of T lymphocytes. This process requires the participation of the CD28 costimulatory receptor. Blockade of CD28 has been demonstrated to prevent inflammation and airway hyperreactivity in a murine model of asthma. Whether this is due specifically to defects in initial T cell activation or whether effector responses are also impaired has not been determined. Using adoptive transfer studies of Ag-specific lymphocytes, we demonstrate that CD28 has a critical role in both the induction and effector phase of allergic airway inflammation. Transfer of in vitro activated and Th2-differentiated Ag-specific lymphocytes from wild-type hosts restored inflammation, but not tissue eosinophilia in CD28-deficient recipients. Furthermore, similarly activated and differentiated CD28-deficient lymphocytes were ineffective at mediating inflammation in wild-type recipients. Secondary cytokine and proliferative responses of activated Th2 cells were highly dependent on CD28 in vitro. Moreover, eosinophil recruitment to both the lung and peritoneum is impaired by the lack of CD28, suggesting a generalized defect in the ability of eosinophils to accumulate at sites of inflammation in vivo. These data identify a novel role for CD28 in the effector phase of allergic airway inflammation and suggest that inhibition of this pathway may be a useful therapeutic intervention in previously sensitized individuals.

Biology and therapeutic potential of the interleukin-4/interleukin-13 signaling pathway in asthma

The future management of patients with allergic asthma is poised to change in the coming one to two decades. This prediction is based on fundamental new insights into the pathogenesis of disease, gained through the study of both humans and experimental models of asthma. These studies have revealed that allergic asthma is an immune-mediated disease which, despite the redundancy characteristic of all immune responses, may be induced through a single dominant signaling cascade called the interleukin (IL)-4/IL-13 signaling pathway. In addition to the cytokine IL-4, this pathway includes IL-13, the cytokine receptor subunit IL-4 receptor alpha (IL-4Ralpha), Janus-associated tyrosine kinases and the transcription factor, signal transducer and activator of transcription 6. The IL-4 signaling pathway controls the most important cellular developmental (afferent) events that underlie asthma. These include T helper (Th) type 2 cell activation, B cell activation and immunoglobulin (Ig) E secretion, mast cell development, and effector (efferent) events related exclusively to immune effects on the lung such as goblet cell metaplasia and airway hyperresponsiveness. Any of the IL-4 signaling molecules are potentially amenable to pharmacological intervention, but a detailed understanding of the entire pathway is required to appreciate their actual potential for drug development. For example, neutralization strategies that target only IL-4 are unlikely to succeed because they leave IL-13 free to continue the signaling cascade. In contrast, neutralization of IL-4Ralpha may represent a more feasible strategy, as it should prevent signaling by both IL-4 and IL-13. The therapeutic potential of targeting intracytoplasmic tyrosine kinases has already been achieved with the use of small molecules, suggesting that this approach may be realistically adopted for the treatment of asthma. However, well designed asthma clinical trials are warranted to determine with certainty, the efficacy of therapies based on IL-4/IL-13 blockade.

CD80, but not CD86 were up-regulated on the spleen-derived dendritic cells from OVA-sensitized and challenged BALB/c mice

Allergen-specific CD4+ T-helper (Th) 2 cells are involved in the induction and effector phase of allergic asthma. It is well established that T cells activation requires interaction of T cell receptor (TCR) and MHC-peptide complex, as well as costimulatory signal delivered by antigen presenting cells (APCs). There is increasing evidence that CD80 (B7.1) and CD86 (B7.2), as the most important costimulatory molecules, are involved in the allergic immune responses. In the present study, we investigated the CD80 and CD86 expression of spleen-derived dendritic cells (DCs) in a murine model of allergic asthma. We first established a murine model of ovalbumin (OVA)-allergic asthma that showed unique histological characteristic of allergic inflammation in the lung, high serum OVA-specific IgE level, high numbers of eosinophils in the bronchoalveolar lavage (BAL) and high production of Type 2 cytokines in the splenic T cells. In this model, we found that CD80 were significantly upregulated on the spleen-derived DCs from OVA-sensitized and challenged mice compared with that from PBS-treated or non-treated mice, while CD86 is not different among three groups. Furthermore, we demonstrated that Th2 immune responses were elicited by these DCs with high expression of CD80, even to nai;ve T cells from non-treated mice. Our results suggest that DCs in the spleen of allergic mice, via upregulation of CD80 might play a pivotal role in the maintenance and amplification of allergic immune response, namely Th2 immune response.

Divergence in NK cell and cyclic AMP regulation of T cell CD40L expression in asthmatic subjects

T cells are central in the pathogenesis of asthma, and the associated ligand, CD40L, plays an important role by increasing production of immunoglobulin E and inflammatory mediators. beta-Adrenoceptor agonists are commonly used in asthma, although little is known regarding effects on CD40L expression and T cell activation. Here, we demonstrate that cyclic adenosine monophosphate (cAMP) and beta-adrenoceptor agonists differentially regulate CD40L in asthma. cAMP increased naïve T cell CD40L expression in asthmatics (9.8+/-8.5 increase in percent CD40L-positive cells), and expression in control subjects was inhibited (7.1+/-6.0 decrease in percent CD40L-positive cells; P< 0.05). Cell depletion and reconstitution experiments were used to determine that cAMP enhancement of CD40L required cell-to-cell contact with an asthma-associated natural killer (NK) cell subset. The NK cell subset expressed elevated levels of CD95, and in vitro-generated CD95+ NK2 cells also produced similar effects on CD40L expression. Our findings suggest that a subset of NK cells with elevated CD95 expression is associated with asthma and can reverse cAMP inhibitory effects on T cell CD40L with the potential to increase disease exacerbation.

CD28/CTLA4 double deficient mice demonstrate crucial role for B7 co-stimulation in the induction of allergic lower airways disease

BACKGROUND

The existence of a third B7-1/B7-2 receptor was postulated in a recent study using a novel mouse strain lacking both CD28 and CTLA4 (CD28/CTLA4-/-).

OBJECTIVE

In the present study, it was investigated if T cell co-stimulation via the putative B7-1/B7-2 receptor plays a role in the induction of Th2-mediated asthma manifestations in mice.

METHODS

BALB/c wild-type, CD28/CTLA4-/- and B7-1/B7-2-/- mice were sensitized and aerosol challenged with ovalbumin (OVA).

RESULTS

At 24 h after the last aerosol, wild-type mice showed airway hyper-responsiveness in vivo and up-regulated levels of serum OVA-specific IgE compared with the situation shortly before OVA challenge. In addition, eosinophil numbers and IL-5 levels in the broncho-alveolar lavage fluid and Th2 cytokine production by lung cells upon OVA re-stimulation in vitro were observed. In agreement with an earlier study, we failed to induce any of the asthma manifestations in B7-1/B7-2-/- mice. Importantly, also CD28/CTLA4-/- mice showed no asthma manifestations upon OVA sensitization and challenge.

CONCLUSION

These data clearly demonstrate that T cell co-stimulation via the putative B7-1/B7-2 receptor appears to have no role in the induction of Th2-mediated asthma manifestations in this murine model and, conversely, that CD28 signalling is crucial.