Innate immune mechanism in allergic asthma

Allergic asthma is a chronic inflammatory disorder of the airways characterized by eosinophilic inflammation, airway hyperresponsiveness, and mucus hypersecretion. Adaptive, antigen-dependent immunity is critical for asthma pathogenesis. Allergic asthma may involve adaptive and innate, antigen-independent immune responses. This review discusses the current evidence that associates innate immunity with allergic asthma pathogenesis. In particular, we focus on the role of innate immune cells (eg, bronchial epithelial cells, alveolar macrophages, and dendritic cells) and molecules (Toll-like and nucleotide-binding oligomerization domain-like receptors) in modifying allergic immune responses.

(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.

Graft Produced Interleukin-6 Functions as a Danger Signal and Promotes Rejection After Transplantation

BACKGROUND

Interleukin (IL)-6 is a pleiotropic cytokine that functions in both the innate and adaptive immune responses. However, the role of IL-6 in allograft rejection remains poorly understood.

METHODS

In this study, we demonstrate a critical role for graft-produced IL-6 in allograft rejection in a murine model of cardiac allograft transplantation.

RESULTS

The results show that IL-6-deficient grafts transplanted into allogeneic wild-type recipients have significantly prolonged survival, approximately three times the survival time of wild-type controls. In contrast, allogeneic cardiac transplants into IL-6-deficient recipients do not have prolonged graft survival, indicating that donor graft cells are the relevant source of IL-6. Our investigation of potential mechanisms shows that graft-produced IL-6 promotes the activation of peripheral CD4 and CD8 T cells. Furthermore, we show that IL-6 deficiency prolongs graft survival only in the presence of CD25+ T cells that have a phenotype consistent with regulatory T cells. Interestingly, IL-6 production by the graft is triggered by antigen-independent innate immune mechanisms.

CONCLUSIONS

Thus, our results suggest the paradigm that graft rejection versus tolerance is determined by a balance between the activation of effector T cells versus immune suppression by regulatory T cells, and that after transplantation, IL-6 functions as a systemic danger signal that overcomes constitutive immune suppression mediated by regulatory T cells and promotes the activation of effector T cells.

Fetal cord blood: aspects of heightened immune responses

Neonatal immune responses have been associated with the development of atopy in childhood. We assessed in cord blood mononuclear cells (CBMC) whether increased allergen/mitogen-induced lymphoproliferation (LP) is associated with pro-allergic Th2 cytokine IL-13 or Th1 cytokine IFN-gamma secretion. We determined whether LP to one allergen is related to heightened lymphocyte function to other allergens/mitogen. CBMC from 135 neonates were stimulated with house dust mite (Derf1), cockroach, ovalbumin, or mitogen. LP to one allergen was associated with significantly increased LP to other allergens/mitogen. Increased Derf1-LP was associated with increased Derf1-induced IL-13 secretion (r = 0.21, p = 0.01). After adjusting for neonatal gender, race, and maternal smoking, Derf1-LP remained associated with Derf1-IL-13 (OR 3.08, 95% CI 1.56-6.10). Increased mitogen-induced proliferation was associated with increased mitogen-induced IL-13 secretion (r = 0.37, p < 0.001). For some individuals, a predisposition to a heightened immune response is already evident at birth. Whether this phenotype results in atopy in childhood warrants further investigation.

Elevated allergen-induced IL-13 secretion predicts IgE elevation in children ages 2-5 years

It is unclear if early immune responses to allergens, specifically Th1 and Th2 cytokine production, predict later immune responses, including increased IgE levels. In a group of children (n = 151) with a parental history of allergy or asthma followed from ages 2 through 5 years, we examined IL-13, IL-4, and IFN-gamma secretion by peripheral blood mononuclear cells in response to phytohemagglutinin (PHA), and to dust mite (Der f 1), cockroach (Bla g 2), and cat (Fel d 1) allergens in relation to elevated IgE. Elevated IgE was defined either as a positive IgE-specific response to at least one allergen (dust mite, cockroach, cat, and ovalbumin) or as an elevated total IgE level above a specified cut-off value. In multivariate logistic regression models including 181 observations made between the age of 2 through 5 years and accounting for repeated measures, we found an association between increased IL-13 secretion in response to Der f 1 and elevated IgE (odds ratio [OR] = 1.21, 95% confidence interval [CI] = 1.09-1.34). Age did not modify this relationship. No association was found between allergen-induced IFN-gamma secretion and IgE production. Among the group of children with measurements made at age 4-5 (n = 70), IL-13 in response to Der f 1 (p = 0.046), and IL-4 in response to PHA (p = 0.04) were increased among children with elevated IgE. In a smaller subset of children with measurements made at both age 2-3 and age 4-5 (n = 36), IL-13 levels at age 2-3 were also significantly increased in response to Der f 1 (p = 0.01) and Fel d 1 (p = 0.002) among those with elevated IgE at age 4-5. In a group of children ages 2-5 years, there is an association between IL-13 and elevated IgE.

Hubs in biological interaction networks exhibit low changes in expression in experimental asthma

Asthma is a complex polygenic disease involving the interaction of many genes. In this study, we investigated the allergic response in experimental asthma. First, we constructed a biological interaction network using the BOND (Biomolecular Object Network Databank) database of literature curated molecular interactions. Second, we mapped differentially expressed genes from microarray data onto the network. Third, we analyzed the topological characteristics of the modulated genes. Fourth, we analyzed the correlation between the topology and biological function using the Gene Ontology classifications. Our results demonstrate that nodes with high connectivity (hubs and superhubs) tend to have low levels of change in gene expression. The significance of our observations was confirmed by permutation testing. Furthermore, our analysis indicates that hubs and superhubs have significantly different biological functions compared with peripheral nodes based on Gene Ontology classification. Our observations have important ramifications for interpreting gene expression data and understanding biological responses. Thus, our analysis suggests that a combination of differential gene expression plus topological characteristics of the interaction network provides enhanced understanding of the biology in our model of experimental 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.

Cord blood cytokines and acute lower respiratory illnesses in the first year of life

OBJECTIVES

Little is known about the relation between cytokine profile at birth and acute lower respiratory illnesses in the first year of life. The purpose of this work was to examine the relation between cytokine secretions by cord blood mononuclear cells and acute lower respiratory illness in a birth cohort of 297 children.

METHODS

Cord blood mononuclear cells were isolated, and secretion of interferon-gamma, interleukin-13, interleukin-10, and tumor necrosis factor-alpha at baseline and in response to allergens (Blatella germanica 2 and Dermatophagoides farinae 1) and mitogen (phytohemagglutinin) were quantified using enzyme-linked immunosorbent assay. Acute lower respiratory illness was defined as a parental report of a diagnosis of bronchiolitis, pneumonia, bronchitis, and/or croup by a health care professional in the first year of life. Differences in the levels of cord blood cytokines between children with and without acute lower respiratory illness were examined using 2-sample Wilcoxon tests. Logistic regression models were used to examine the relation between various categories of cord blood cytokines and acute lower respiratory illness.

RESULTS

Median levels of interferon-gamma secreted by cord blood mononuclear cells in response to Blatella germanica 2 and Dermatophagoides farinae 1 were higher among children without acute lower respiratory illness as compared with children with acute lower respiratory illness. After adjustment for other covariates, the odds of acute lower respiratory illness was reduced among children in the top category (at or more than the median of detectable values) of interferon-gamma level, significantly so in response to Blatella germanica 2.

CONCLUSIONS

In a cohort of children from the general population, we found that upregulated interferon-gamma secretion at birth is associated with reduced risk of acute lower respiratory illness in the first year of life.

Cutting Edge: Deficiency of Macrophage Migration Inhibitory Factor Impairs Murine Airway Allergic Responses

Increased levels of macrophage migration inhibitory factor (MIF) in serum, sputum, and bronchioalveolar lavage fluid (BALF) from asthmatic patients and time/dose-dependent expression of MIF in eosinophils in response to phorbol myristate acetate suggest the participation of MIF in airway inflammation. In this study, we examined inflammation in OVA-sensitized mouse lungs in wild-type and MIF-deficient mice (MIF(-/-)). We report increased MIF in the lung and BALF of sensitized wild-type mice. MIF(-/-) mice demonstrated significant reductions in serum IgE and alveolar inflammatory cell recruitment. Reduced Th1/Th2 cytokines and chemokines also were detected in serum or BALF from MIF(-/-) mice. Importantly, alveolar macrophages and mast cells, but not dendritic cells or splenocytes, from MIF(-/-) mice demonstrated impaired CD4+ T cell activation, and the reconstitution of wild-type mast cells in MIF(-/-) mice restored the phenotype of OVA-induced airway inflammation, revealing a novel and essential role of mast cell-derived MIF in experimentally induced airway allergic diseases.

The combined effects of zafirlukast, prednisone, and inhaled budesonide on IL-13 and IFN-gamma secretion

Therapy for asthma often includes the combined use of glucocorticoids and leukotriene receptor antagonists. The short-term, combined effects of these drugs on cytokine secretion and lymphocyte proliferation are ill-defined. The aim of this study was to analyze allergen and mitogen-induced cytokine secretion and lymphocyte proliferation in asthmatics and to determine the effect of combined therapy on these immune responses. Peripheral blood mononuclear cells were isolated from mild, persistent adult asthmatics (n = 28) and analyzed for cat allergen (Fel d 1) and mitogen (phytohemagglutinin) induced IL-13 and IFN-gamma secretion and lymphocyte proliferation. Samples were analyzed before and after 10 days of therapy with oral zafirlukast, prednisone (0.5 mg/kg/day), and inhaled budesonide (1600 mcg/day). Both Fel d 1 and mitogen stimulation resulted in IL-13 and IFN-gamma secretion. Combination drug therapy resulted in a significant decrease in allergen-induced IFN-gamma secretion (p = 0.018) and allergen-specific lymphocyte proliferation (p = 0.02), while IL-13 secretion was unchanged (p = 0.109). This study indicates a role for Th1 cytokines as well as Th2 cytokines in the allergic response.

Prenatal, perinatal, and heritable influences on cord blood immune responses

BACKGROUND

Maternal and perinatal environmental exposures, as well as inherited factors, may influence neonatal immune responses.

OBJECTIVE

To determine relations of maternal and perinatal exposures to antigen-specific cord blood lymphoproliferative responses.

METHODS

In 427 newborns from a Boston pregnancy/birth cohort, lymphoproliferative responses in cord blood mononuclear cells to stimulation with cockroach (Bla g 2), house dust mite (Der f 1), ovalbumin, and mitogen phytohemagglutinin were measured as stimulation index (SI). We used the Wilcoxon rank sum and chi2 tests to evaluate predictors of ovalbumin SI as a continuous ranked or dichotomous outcome. We used t test and Spearman correlation for univariate testing and linear regression to evaluate predictors of natural log-transformed Bla g 2, Der f 1, and phytohemagglutinin SI. Logistic multivariate regression was applied to evaluate predictors of Bla g 2, Der f 1, and phytohemagglutinin SI dichotomized at 2 or at the median for phytohemagglutinin.

RESULTS

Maternal smoking during pregnancy, inadequate or excessive maternal weight gain during pregnancy, neonate black race/ethnicity (compared with white), and Apgar score less than 8 were each independently associated with increased cord blood mononuclear cell proliferative responses to stimulation with Bla g 2 and/or Der f 1. Maternal history of asthma was associated only with increased lymphoproliferative response to ovalbumin stimulation.

CONCLUSIONS

Distinct fetal and perinatal exposures and black race/ethnicity may be associated with increased cord blood lymphoproliferative responses. The implications of these findings for future development of allergy or asthma are, as yet, unknown.

Neonatal immune responses to TLR2 stimulation: influence of maternal atopy on Foxp3 and IL-10 expression

Background

Maternal atopic background and stimulation of the adaptive immune system with allergen interact in the development of allergic disease. Stimulation of the innate immune system through microbial exposure, such as activation of the innate Toll-like-receptor 2 (TLR2), may reduce the development of allergy in childhood. However, little is known about the immunological effects of microbial stimulation on early immune responses and in association with maternal atopy.

Methods

We analyzed immune responses of cord blood mononuclear cells (CBMC) from 50 healthy neonates (31 non-atopic and 19 atopic mothers). Cells were stimulated with the TLR2 agonist peptidoglycan (Ppg) or the allergen house dust mite Dermatophagoides farinae (Derf1), and results compared to unstimulated cells. We analyzed lymphocyte proliferation and cytokine secretion of CBMC. In addition, we assessed gene expression associated with T regulatory cells including the transcription factor Foxp3, the glucocorticoid-induced TNF receptor (GITR), and the cytotoxic lymphocyte antigen 4 (CTLA4). Lymphocyte proliferation was measured by ³H-Thymidine uptake, cytokine concentrations determined by ELISA, mRNA expression of T cell markers by real-time RT-PCR.

Results

Ppg stimulation induced primarily IL-10 cytokine production, in addition to IFN-γ, IL-13 and TNF-α secretion. GITR was increased following Ppg stimulation (p = 0.07). Ppg-induced IL-10 production and induction of Foxp3 were higher in CBMC without, than with maternal atopy (p = 0.04, p = 0.049). IL-10 production was highly correlated with increased expression of Foxp3 (r = 0.53, p = 0.001), GITR (r = 0.47, p = 0.004) and CTLA4 (r = 0.49, p = 0.003), independent of maternal atopy.

Conclusion

TLR2 stimulation with Ppg induces IL-10 and genes associated with T regulatory cells, influenced by maternal atopy. Increased IL-10 and Foxp3 induction in CBMC of non-atopic compared to atopic mothers, may indicate an increased capacity to respond to microbial stimuli.

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.

Associations of cord blood fatty acids with lymphocyte proliferation, IL-13, and IFN-gamma

BACKGROUND

N-3 and n-6 polyunsaturated fatty acids (PUFAs) have been hypothesized to have opposing influences on neonatal immune responses that might influence the risk of allergy or asthma. However, both n-3 eicosapentaenoic acid (EPA) and n-6 arachidonic acid (AA) are required for normal fetal development.

OBJECTIVE

We evaluated whether cord blood fatty acid levels were related to neonatal immune responses and whether n-3 and n-6 PUFA responses differed.

METHODS

We examined the relation of cord blood plasma n-3 and n-6 PUFAs (n = 192) to antigen- and mitogen-stimulated cord blood lymphocyte proliferation (n = 191) and cytokine (IL-13 and IFN-gamma; n = 167) secretion in a US birth cohort.

RESULTS

Higher levels of n-6 linoleic acid were correlated with higher IL-13 levels in response to Bla g 2 (cockroach, P = .009) and Der f 1 (dust mite, P = .02). Higher n-3 EPA and n-6 AA levels were each correlated with reduced lymphocyte proliferation and IFN-gamma levels in response to Bla g 2 and Der f 1 stimulation. Controlling for potential confounders, EPA and AA had similar independent effects on reduced allergen-stimulated IFN-gamma levels. If neonates had either EPA or AA levels in the highest quartile, their Der f 1 IFN-gamma levels were 90% lower (P = .0001) than those with both EPA and AA levels in the lowest 3 quartiles. Reduced AA/EPA ratio was associated with reduced allergen-stimulated IFN-gamma level.

CONCLUSION

Increased levels of fetal n-3 EPA and n-6 AA might have similar effects on attenuation of cord blood lymphocyte proliferation and IFN-gamma secretion.

CLINICAL IMPLICATIONS

The implications of these findings for allergy or asthma development are not yet known.

Infant home endotoxin is associated with reduced allergen-stimulated lymphocyte proliferation and IL-13 production in childhood

BACKGROUND

Infant endotoxin exposure has been proposed as a factor that might protect against allergy and the early childhood immune responses that increase the risk of IgE production to allergens.

OBJECTIVE

Using a prospective study design, we tested the hypothesis that early-life endotoxin exposure is associated with allergen- and mitogen-induced cytokine production and proliferative responses of PBMCs isolated from infants with a parental history of physician-diagnosed asthma or allergy.

METHODS

We assessed household dust endotoxin at age 2 to 3 months and PBMC proliferative and cytokine responses to cockroach allergen (Bla g 2), dust mite allergen (Der f 1), cat allergen (Fel d 1), and the nonspecific mitogen PHA at age 2 to 3 years.

RESULTS

We found that increased endotoxin levels were associated with decreased IL-13 levels in response to cockroach, dust mite, and cat allergens, but not mitogen stimulation. Endotoxin levels were not correlated with allergen- or mitogen-induced IFN-gamma, TNF-alpha, or IL-10. Increased endotoxin levels were associated with decreased lymphocyte proliferation after cockroach allergen stimulation. An inverse, although nonsignificant, association was also found between endotoxin and proliferation to the other tested stimuli.

CONCLUSION

Increased early-life exposure to household endotoxin was associated with reduced allergen-induced production of the TH2 cytokine IL-13 and reduced lymphoproliferative responses at age 2 to 3 years in children at risk for allergy and asthma. Early-life endotoxin-related reduction of IL-13 production might represent one pathway through which increased endotoxin decreases the risk of allergic disease and allergy in later childhood.

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.

Epigenetic approaches to cancer therapy

Histone deacetylation and DNA methylation have a central role in the control of gene expression, including transcriptional repression of tumour suppressor genes. Loss of DNA mismatch repair due to methylation of the hMLH1 gene promoter results in resistance to cisplatin in vitro and in vivo. The cisplatin-resistant cell line A2780/cp70 is 8-fold more resistant to cisplatin than the non-resistant cell line, and has the hMLH1 gene methylated. Treatment with an inhibitor of DNA methyltransferase, DAC (2-deoxy-5'-azacytidine), results in a partial reversal of DNA methylation, re-expression of MLH1 (mutL homologue 1) and sensitization to cisplatin both in vitro and in vivo. PXD101 is a novel hydroxamate type histone deacetylase inhibitor that shows antitumour activity in vivo and is currently in phase I clinical evaluation. Treatment of A2780/cp70 tumour-bearing mice with DAC followed by PXD101 results in a marked increase in the number of cells that re-express MLH1. Since the clinical use of DAC may be limited by toxicity and eventual re-methylation of genes, we suggest that the combination of DAC and PXD101 could have a role in increasing the efficacy of chemotherapy in patients with tumours that lack MLH1 expression due to hMLH1 gene promoter methylation.

Surfactant protein D deficiency influences allergic immune responses

BACKGROUND

The collectin surfactant protein D (SP-D) confers protection against pulmonary infection and inflammation. Recent data suggest a role for SP-D in the modulation of allergic inflammation.

OBJECTIVE

The aim of this study is to characterize the immune responses of SP-D-deficient (SP-D(-/-)) mice in a kinetic model of allergic inflammation. We determined whether allergic parameters were enhanced in SP-D(-/-) mice in vivo. Further, we examined whether functional immune responses in vitro such as lymphocyte proliferation (LP) and cytokine production were modulated in the absence of SP-D.

METHODS

In vivo, wild-type (WT) and SP-D(-/-) mice were sensitized and challenged with the allergen ovalbumin (OVA) and assessed for allergic parameters (bronchoalveolar lavage (BAL) eosinophils, IL-13 production, pulmonary IFN-gamma, IL-10 expression) at early time points (1 and 3 days of challenge) in comparison with late time points (7 days of challenge). In vitro, spleen cells from WT and SP-D(-/-) mice were stimulated with the mitogen concanavalin A (ConA) and lipid A (LpA) and analysed for LP, IL-13 and IFN-gamma production. Toll-like receptor 4 (TLR4), ligand for LpA, was assessed by mRNA expression and immunohistochemistry in vivo.

RESULTS

Following allergen exposure in vivo, SP-D(-/-) mice expressed higher BAL eosinophils and IL-13 concentrations and lower IFN-gamma expression at early time points compared with WT mice. IL-10 expression was increased at early time points in SP-D(-/-) compared with WT mice. Allergen-induced TLR4 expression was increased in WT, but not in SP-D(-/-) mice. After stimulation with LpA and ConA in vitro LP was increased and IFN-gamma concentration was decreased in SP-D(-/-) mice.

CONCLUSION

SP-D may be critical for the modulation of early stages of allergic inflammation in vivo.

TLR2 and TLR4 stimulation differentially induce cytokine secretion in human neonatal, adult, and murine mononuclear cells

Toll-like receptor 2 (TLR2) and TLR4 signaling may induce differential secretion of T helper 1 (Th1) and Th2 cytokines, potentially influencing the development of autoimmune or atopic diseases. To date, the influence of the type of stimulus, timing, and dose of TLR2 and TLR4 ligands on cytokine secretion has not been well established. We tested whether the innate stimuli peptidoglycan (Ppg, TLR2 agonist) and lipid A (LpA, TLR4 agonist) differentially affect the secretion of interleukin-13 (IL-13) (Th2) and interferon-gamma (IFN-gamma) (Th1). Further, we examined the influence of the maturity of the immune system, species, dose, and timing of stimuli in human cord and adult peripheral blood mononuclear cells (PBMC) and murine cells in vitro and in vivo. Stimulation with Ppg induced the secretion of both IL-13 and IFN-gamma, influenced by time and dose in neonates, adults, and mice. In contrast, stimulation with LpA induced primarily time-independent and dose-independent production of IFN-gamma. Pulmonary administration of Ppg in vivo in mice resulted in secretion of IL-13, whereas administration of LpA resulted in secretion of IFN-gamma in bronchoalveolar lavage (BAL). Therefore, TLR2 and TLR4 stimuli differentially influence IL-13 and IFN-gamma secretion in neonates, adults, and mice, supporting a critical role for innate stimuli in the modulation of cytokine responses.

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.

Analysis of the Major Histocompatibility Complex in Graft Rejection Revisited by Gene Expression Profiles

BACKGROUND

The precise role of major histocompatibility complex (MHC) molecules in graft rejection remains incompletely understood. The important role of foreign peptides in the alloimmune response was recently recognized.

METHODS

We performed a comparative study of the functions of minor antigens Class I, Class II, and CD1 in murine cardiac allograft rejection by investigating the expression of a large panel of immune and inflammatory genes. To investigate the role of MHC Class II and I, our protocol analyzed allograft recipients deficient in MHC Class II and b2 microglobulin (b2-M), a critical component of the Class I heterodimer. We also included CD1 deficient recipients to differentiate effects in the beta2-M deficient strain due to CD1 deficiency versus the combined inactivation of CD1 and Class I. The serum cytokines tumor necrosis factor (TNF)-alpha interleukin (IL)-6, interferon (IFN)-gamma and IL-1beta were evaluated posttransplant by ELISA. The intragraft expression of 55 chemokines, chemokine receptors, and CD markers were measured by ribonuclease protection assay. The data were analyzed through hierarchical clustering dendrograms and self-organizing maps.

RESULTS

The analysis indicates that each gene deficiency induces both the upregulation and the downregulation of distinct subsets of genes and that similar kinetics of rejection can be attributed to different molecular mechanisms.

CONCLUSIONS

The study provides novel insights into the role of classical and non-classical MHC molecules in graft rejection.