Blockade of allergic airway inflammation following systemic treatment with a B7-dendritic cell (PD-L2) cross-linking human antibody

Allergic disease, corticosteroid use, and risk of Hodgkin lymphoma: A United Kingdom nationwide case-control study

BACKGROUND

Immunodeficiency syndromes (acquired/congenital/iatrogenic) are known to increase Hodgkin lymphoma (HL) risk, but the effects of allergic immune dysregulation and corticosteroids are poorly understood.

OBJECTIVE

We sought to assess the risk of HL associated with allergic disease (asthma, eczema, and allergic rhinitis) and corticosteroid use.

METHODS

We conducted a case-control study using the United Kingdom Clinical Practice Research Datalink (CPRD) linked to hospital data. Multivariable logistic regression investigated associations between allergic diseases and HL after adjusting for established risk factors. Potential confounding or effect modification by steroid treatment were examined.

RESULTS

One thousand two hundred thirty-six patients with HL were matched to 7416 control subjects. Immunosuppression was associated with 6-fold greater odds of HL (adjusted odds ratio [aOR], 6.18; 95% CI, 3.04-12.57), with minimal change after adjusting for steroids. Any prior allergic disease or eczema alone was associated with 1.4-fold increased odds of HL (aOR, 1.41 [95% CI, 1.24-1.60] and 1.41 [95% CI, 1.20-1.65], respectively). These associations decreased but remained significant after adjustment for steroids (aOR, 1.25 [95% CI, 1.09-1.43] and 1.27 [95% CI, 1.08-1.49], respectively). There was no effect modification by steroid use. Previous steroid treatment was associated with 1.4-fold greater HL odds (aOR, 1.38; 95% CI, 1.20-1.59).

CONCLUSIONS

In addition to established risk factors (immunosuppression and infectious mononucleosis), allergic disease and eczema are risk factors for HL. This association is only partially explained by steroids, which are associated with increased HL risk. These findings add to the growing evidence that immune system malfunction after allergic disease or immunosuppression is central to HL development.

PDCD1 PD-1.3 polymorphism and allergic bronchial asthma in Russian and Buryat patients

OBJECTIVE

The programmed death-1 receptor, PD-1, is a negative regulator of T-cell activation. The PD-1.3 polymorphism of the PD-1 gene (PDCD1) has been previously shown to be associated with several autoimmune and inflammatory disorders including systemic lupus erythematosus and multiple sclerosis. We examined for the first time PD-1.3 association with another inflammatory disease with strong immune component, IgE-mediated bronchial asthma, its severity and its biochemical markers (total serum IgE and IL-4).

METHODS

PD-1.3 G/A was genotyped by PCR-RFLP analysis using two different populations: Caucasian (492 Russian individuals) and Asian (276 Buryat individuals).

RESULTS

We found a significant association of the PD-1.3 polymorphism with IgE-mediated bronchial asthma and total serum IgE level in the Russian population. Combined genotype AA+AG was correlated with risk of developing allergic bronchial asthma (OR = 1.78, 95% CI 1.13-2.78, p = 0.011) and lower concentrations of total serum IgE (p = 0.001) compared with the wild-type genotype GG. However, PD-1.3 was not polymorphic in the Buryat population.

CONCLUSIONS

PD-1.3 polymorphism of the PD-1 gene (PDCD1) may contribute to the development of allergic asthma in the Russians but not in the Buryats. Our results could be helpful for a better understanding of the effect of this polymorphism on the development of diseases with strong immune components.

Programmed cell death ligand 2 regulates TH9 differentiation and induction of chronic airway hyperreactivity

BACKGROUND

Asthma is defined as a chronic inflammatory disease of the airways; however, the underlying physiologic and immunologic processes are not fully understood.

OBJECTIVE

The aim of this study was to determine whether TH9 cells develop in vivo in a model of chronic airway hyperreactivity (AHR) and what factors control this development.

METHOD

We have developed a novel chronic allergen exposure model using the clinically relevant antigen Aspergillus fumigatus to determine the time kinetics of TH9 development in vivo.

RESULTS

TH9 cells were detectable in the lungs after chronic allergen exposure. The number of TH9 cells directly correlated with the severity of AHR, and anti-IL-9 treatment decreased airway inflammation. Moreover, we have identified programmed cell death ligand (PD-L) 2 as a negative regulator of TH9 cell differentiation. Lack of PD-L2 was associated with significantly increased TGF-β and IL-1α levels in the lungs, enhanced pulmonary TH9 differentiation, and higher morbidity in the sensitized mice.

CONCLUSION

Our findings suggest that PD-L2 plays a pivotal role in the regulation of TH9 cell development in chronic AHR, providing novel strategies for modulating adaptive immunity during chronic allergic responses.

Synthesized OVA323-339MAP octamers mitigate OVA-induced airway inflammation by regulating Foxp3 T regulatory cells

Background

Antigen-specific immunotherapy (SIT) has been widely practiced in treating allergic diseases such as asthma. However, this therapy may induce a series of allergic adverse events during treatment. Peptide immunotherapy (PIT) was explored to overcome these disadvantages. We confirmed that multiple antigen peptides (MAPs) do not cause autoimmune responses, which led to the presumption that MAPs intervention could alleviate allergic airway inflammation without inducing adverse effects.

Results

In this study, synthesized OVA_323-339MAP octamers were subcutaneously injected into ovalbumin (OVA)-sensitized and -challenged Balb/c mice to observe its effect on allergic airway inflammation, Th2 immune response, and immune regulating function. It was confirmed that OVA sensitization and challenge led to significant peritracheal inflammatory, cell infiltration, and intensive Th2 response. Treatment of OVA_323-339MAP octomers in the airway inflammation mice model increased CD4⁺CD25⁺Foxp3⁺ T regulatory (Treg) cells and their regulatory function in peripheral blood, mediastinal draining lymph nodes, and the spleen. Furthermore, OVA_323-339MAP increased IL-10 levels in bronchial alveolar lavage fluid (BALF); up-regulated the expression of IL-10, membrane-bound TGF-β1, as well as Foxp3 in lung tissues; and up-regulated programmed death-1 (PD-1) and cytotoxic T lymphocyte associated antigen 4 (CTLA-4) on the surface of Treg cells. These results were further correlated with the decreased OVA specific immunoglobulin E (sIgE) level and the infiltration of inflammatory cells such as eosinophils and lymphocytes in BALF. However, OVA_323-339 peptide monomers did not show any of the mentioned effects in the same animal model.

Conclusions

Our study indicates that OVA_323-339MAP had significant therapeutic effects on mice allergic airway inflammation by regulating the balance of Th1/Th2 response through Treg cells in vivo.

Role of PD-L1 and PD-L2 in allergic diseases and asthma

Asthma is the result of chronic airway inflammation associated predominantly with CD4+ cells, eosinophils, mast cells, and basophils. Several T-cells subsets, including NKT cells, play a critical role in orchestrating the inflammation in the airways predominantly, by secreting interleukin-4 and interleukin-13. Recently, programmed death-1 (PD-1) with its ligands, programmed death ligand B7H1 (PD-L1) and B7DC (PD-L2), was shown to regulate T-cell activation and tolerance. PD-1 has been characterized as a negative regulator of conventional CD4+T cells. In addition, the relative roles of PD-L1 and PD-L2 in regulating the activation and function of T cells have recently been characterized. Recent studies have demonstrated that PD-L1 and PD-L2 have important but opposing roles in modulating and polarizing T-cell functions in airway hyperreactivity. Whereas the severity of asthma is greatly enhanced in absence of PD-L2, PD-L1 deficiency resulted in reduced airway hyperresponsiveness and only minimal inflammation. This observation is partially because of the polarization of NKT cells in PD-L1- and PD-L2-deficient mice. This review will discuss the recent literature regarding the role of PD-L1 and PD-L2 in allergic disease and asthma. Current understanding of the role of PD ligands in allergic asthma gives impetus to the development of novel therapeutic approaches.

Natural autoantibodies: immune homeostasis and therapeutic intervention

The importance of natural autoantibodies reacting with self-antigens has long been neglected, as tolerance to self was believed to be primarily dependent on the deletion of autoreactive clones during ontogeny. However, it is now well established that autoreactive antibodies and B- and T-cells are present in healthy individuals. Research into the properties of natural autoantibodies and their role in immune homeostasis has been extensively investigated for a number of years. This information should lead towards the therapeutic exploitation of natural autoantibodies in the immunotherapy of autoimmune and inflammatory disorders.

PD-L1 and PD-L2 modulate airway inflammation and iNKT-cell-dependent airway hyperreactivity in opposing directions

Interactions of the inhibitory receptor programmed death-1 (PD-1) with its ligands, programmed death ligand (PD-L)1 and PD-L2, regulate T-cell activation and tolerance. In this study, we investigated the role of PD-L1 and PD-L2 in regulating invariant natural killer T (iNKT)-cell-mediated airway hyperreactivity (AHR) in a murine model of asthma. We found that the severity of AHR and airway inflammation is significantly greater in PD-L2(-/-) mice compared with wild-type mice after either ovalbumin (OVA) sensitization and challenge or administration of alpha-galactosylceramide (alpha-GalCer). iNKT cells from PD-L2(-/-) mice produced significantly more interleukin (IL)-4 than iNKT cells from control mice. Moreover, blockade of PD-L2 interactions of wild-type iNKT cells in vitro with monoclonal antibodies (mAbs) resulted in significantly enhanced levels of IL-4 production. In contrast, PD-L1(-/-) mice showed significantly reduced AHR and enhanced production of interferon-gamma (IFN-gamma) by iNKT cells. iNKT-deficient Jalpha18(-/-) mice reconstituted with iNKT cells from PD-L2(-/-) mice developed high levels of AHR, whereas mice reconstituted with iNKT cells from PD-L1(-/-) mice developed lower levels of AHR compared with control. As PD-L2 is not expressed on iNKT cells but rather is expressed on lung dendritic cells (DCs), in which its expression is upregulated by allergen challenge or IL-4, these findings suggest an important role of PD-L2 on lung DCs in modulating asthma pathogenesis. These studies also indicate that PD-L1 and PD-L2 have important but opposing roles in the regulation of AHR and iNKT-cell-mediated activation.

The role of costimulatory molecules in allergic disease and asthma

The prevalence of allergic diseases has increased rapidly in recent years. It is well established that the deleterious allergic response is initiated by T-cell recognition of major histocompatibility class II-peptide complexes at the surface of antigen-presenting cells. While this first signal gives antigen specificity to the adaptive immune response, a second nonspecific costimulatory signal is required by T cells to become fully activated. This signal is provided by interactions between antigen-presenting cells and T cells through molecules borne at the surfaces of the two cell types. Depending on the type of molecules involved, this secondary signal can promote the development of an inflammatory allergic reaction or may favor immune regulation. Several molecules of the B7 family (CD80, CD86, PD-1, ICOS, CTLA-4) and tumor necrosis factor receptor family (OX40, CD30, 4-1BB, Fas, CD27, CD40) play an important role in delivering costimulatory signals in early and late phases of allergic response. Therefore, costimulatory molecules involved in promotion or prevention of allergic immune responses are potential targets for the development of novel therapeutic approaches. This review aims to recapitulate our current understanding of the relationship between allergic diseases and costimulatory molecules.

Allergic airway inflammation and susceptibility to pneumococcal pneumonia in a murine model with real-time in vivo evaluation

The relationship between allergic airway inflammation and pneumococcal pneumonia is not well understood. We assessed susceptibility to experimental pneumococcal pneumonia in mice with and without allergic airway inflammation. Susceptibility to pneumococcal pneumonia was evaluated by challenging mice with a bioluminescent Streptococcus pneumoniae strain after sensitization with ovalbumin (OVA), with subsequent monitoring of pneumococcal infection using real-time photonic imaging. Of 46 OVA-sensitized mice challenged with pneumococci, 13 (28%) developed imaging findings consistent with pneumococcal pneumonia. In comparison, 28 (57%) of 49 non-sensitized control mice developed pneumococcal pneumonia (P = 0.005). While none of the control group developed meningitis (0%, none of 28), two mice in the OVA-sensitized group developed meningitis (15.4%, two of 13) (P = 0.09). The mean bacterial count in the lung was significantly lower in the OVA-sensitized than the non-sensitized group (8.26 +/- 0.69 versus 9.21 +/- 0.67 log(10) colony-forming units (CFU)/g, P = 0.002). There was a trend towards the mean bacterial count in the spleen being higher in the OVA-sensitized versus the non-sensitized group (8.14 +/- 0.89 versus 7.45 +/- 1.07 log(10) CFU/g, P = 0.071). A high level of interleukin (IL)-4 in lung homogenates was associated with risk of pneumococcal infection independent of sensitization with OVA (odds ratio: 49.7, 95% confidence interval 2.92-846.5, per increment of 1.0 pg/ml). In the murine model studied, acute allergic airway inflammation reduced susceptibility to pneumococcal pneumonia. IL-4 may increase the risk of pneumococcal pneumonia independently of allergic airway inflammation.

Indirect recruitment of a CD40 signaling pathway in dendritic cells by B7-DC cross-linking antibody modulates T cell functions

The human IgM B7-DC XAb protects mice from tumors in both therapeutic and prophylactic settings. Its mechanism of action is mediated by its binding to B7-DC/PD-L2 molecules on the surface of dendritic cells (DCs) to induce a multimolecular cap and subsequent activation of signaling cascades that determine a unique combination of DC phenotypes. One such phenotype, the B7-DC XAb-induced antigen accumulation in mTLR-matured DCs, has been linked to signaling through TREM-2, but the signals required for other DC phenotypes critical for the therapeutic effects in animal models remain unclear. Here, FRET and co-immunoprecipitation studies show that CD40 is recruited to the multi-molecular complex by B7-DC XAb. Signals emanating from CD40 are important, as CD40^−/− DCs treated with B7-DC XAb (DC^XAb) activated DAP12, but failed to activate NFκB, and were not protected from cell death upon cytokine withdrawal or treatment with Vitamin D₃. CD40^−/− DC^XAb also failed to secrete IL-6 and were unable to support the conversion of T regulatory cells into IL-17+ effector T cells in vitro. Importantly, the expression of CD40 was required for the overall ability of B7-DC XAb to induce anti-tumor CTL, to provide protection from a number of tumor types, and for DC^XAb to be effective anti-tumor vaccines in vivo. These results indicate that B7-DC XAb modulation of DC phenotypes is through its ability to indirectly recruit common signaling molecules and elements of their endogenous signaling pathways through targeted binding to a cell-specific surface determinant.

TREM-2 mediated signaling induces antigen uptake and retention in mature myeloid dendritic cells

Myeloid dendritic cells (mDC) activated with a B7-DC-specific cross-linking IgM Ab (B7-DC XAb) take up and retain Ag and interact with T cell compartments to affect a number of biologic changes that together cause strong antitumor responses and blockade of inflammatory airway disease in animal models. The molecular events mediating the initial responses in mDC remain unclear. In this study we show that B7-DC XAb caused rapid phosphorylation of the adaptor protein DAP12 and intracellular kinases Syk and phospholipase C-gamma1. Pretreatment of mDC with the Syk inhibitor piceatannol blocked B7-DC XAb-induced Ag uptake with a concomitant loss of tumor protection in mice. Vaccination with tumor lysate-pulsed wild-type B7-DC XAb-activated mDC, but not TREM-2 knockout XAb-activated mDC, protected mice from lethal melanoma challenge. Multimolecular caps appeared within minutes of B7-DC XAb binding to either human or mouse mDC, and FRET analysis showed that class II, CD80, CD86, and TREM-2 are recruited in tight association on the cell surface. When TREM-2 expression was reduced in wild-type mDC using short hairpin RNA or by using mDC from TREM-2 knockout mice, in vitro DC failed to take up Ag after B7-DC XAb stimulation. These results directly link TREM-2 signaling with one change in the mDC phenotype that occurs in response to this unique Ab. The parallel signaling events observed in both human and mouse mDC support the hypothesis that B7-DC cross-linking may be useful as a therapeutic immune modulator in human patients.

T-bet expression by dendritic cells is required for the repolarization of allergic airway inflammation

By cross-linking B7-DC on dendritic cells (DC) the human IgM antibody (B7-DC XAb) shifts polarized immune responses from Th2 to Th1 in an antigen-specific manner. The molecular determinants governing the ability of DC to reprogram the polarity of T cell recall responses are not yet known. In addition to the expected role of T-bet expressed by T cells in regulating Th1 responses, we find using in vitro assays and an established in vivo model of allergic airway inflammation that T-bet expression by DC is also required for the polarity shift promoted by B7-DC XAb. T-bet expression by both T cells and DC is critically important for B7-DC XAb-induced down-regulation of IL-4, up-regulation of IFN-gamma and suppression of allergic airway inflammation. Moreover, retroviral reconstitution of T-bet expression in T-bet-deficient DC rescued their ability to modulate both naive and memory T-cell responses from Th2 to Th1. Our observations further our understanding of the critical mediators controlling the ability of DC to modify the responses of previously activated T cells and reveal the interesting use of the same transcription factor to regulate the inductive phenotype of DC and the inducible phenotype of T cells.

Reprogrammed FoxP3+ T regulatory cells become IL-17+ antigen-specific autoimmune effectors in vitro and in vivo

Lymphocyte differentiation from naive CD4(+) T cells into mature Th1, Th2, Th17, or T regulatory cell (Treg) phenotypes has been considered end stage in character. In this study, we demonstrate that dendritic cells (DCs) activated with a novel immune modulator B7-DC XAb (DC(XAb)) can reprogram Tregs into T effector cells. Down-regulation of FoxP3 expression after either in vitro or in vivo Treg-DC(XAb) interaction is Ag-specific, IL-6-dependent, and results in the functional reprogramming of the mature T cell phenotype. The reprogrammed Tregs cease to express IL-10 and TGFbeta, fail to suppress T cell responses, and gain the ability to produce IFN-gamma, IL-17, and TNF-alpha. The ability of IL-6(+) DC(XAb) and the inability of IL-6(-/-) DC(XAb) vaccines to protect animals from lethal melanoma suggest that exogenously modulated DC can reprogram host Tregs. In support of this hypothesis and as a test for Ag specificity, transfer of DC(XAb) into RIP-OVA mice causes a break in immune tolerance, inducing diabetes. Conversely, adoptive transfer of reprogrammed Tregs but not similarly treated CD25(-) T cells into naive RIP-OVA mice is also sufficient to cause autoimmune diabetes. Yet, treatment of normal mice with B7-DC XAb fails to elicit generalized autoimmunity. The finding that mature Tregs can be reprogrammed into competent effector cells provides new insights into the plasticity of T cell lineage, underscores the importance of DC-T cell interaction in balancing immunity with tolerance, points to Tregs as a reservoir of autoimmune effectors, and defines a new approach for breaking tolerance to self Ags as a strategy for cancer immunotherapy.

Induction of B7-H1 and B7-DC expression on airway epithelial cells by the Toll-like receptor 3 agonist double-stranded RNA and human rhinovirus infection: In vivo and in vitro studies

BACKGROUND

T-cell infiltration of the epithelium is a key feature of chronic rhinosinusitis and asthma. Viral infections are an important cause of disease exacerbations. We have found virus-induced expression of T cell-interacting ligands, B7 homolog costimulatory molecules, on airway epithelium.

OBJECTIVE

We tested the ability of human rhinovirus (HRV) 16 and double-stranded RNA (dsRNA) to alter the expression of B7 homologs on human airway epithelial cells.

METHODS

BEAS2B and primary human airway epithelial cells were exposed in vitro to dsRNA (25 microg/mL) or HRV-16, and then expression of cell-surface protein and mRNA for B7 homologs was assessed by means of flow cytometry and real-time PCR, respectively. Additionally, human subjects were infected with HRV-16 in vivo, and mRNA for B7 homologs was assessed by means of real-time PCR in fresh nasal epithelial cell scrapings obtained before and daily up to 4 days after infection.

RESULTS

dsRNA exposure of BEAS2B and human primary bronchial epithelial cells resulted in increased levels of cell-surface and mRNA expression of B7-H1 and B7-DC but not B7-H2 or B7-H3. Exposure of primary cells to HRV-16 resulted in induction of cell-surface expression of B7-H1 and B7-DC. Pretreatment with fluticasone propionate failed to suppress the induction of B7-H1 and B7-DC. Nasal scrapings taken at the time of peak symptom scores (3 days) after infection of 6 human subjects with HRV-16 displayed selective induction of levels of mRNA for B7-H1 and B7-DC.

CONCLUSION

These data show that HRV-16 infection or exposure to dsRNA induces epithelial B7-H1 and B7-DC.

PD-1 and its ligands in tolerance and immunity

Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, deliver inhibitory signals that regulate the balance between T cell activation, tolerance, and immunopathology. Immune responses to foreign and self-antigens require specific and balanced responses to clear pathogens and tumors and yet maintain tolerance. Induction and maintenance of T cell tolerance requires PD-1, and its ligand PD-L1 on nonhematopoietic cells can limit effector T cell responses and protect tissues from immune-mediated tissue damage. The PD-1:PD-L pathway also has been usurped by microorganisms and tumors to attenuate antimicrobial or tumor immunity and facilitate chronic infection and tumor survival. The identification of B7-1 as an additional binding partner for PD-L1, together with the discovery of an inhibitory bidirectional interaction between PD-L1 and B7-1, reveals new ways the B7:CD28 family regulates T cell activation and tolerance. In this review, we discuss current understanding of the immunoregulatory functions of PD-1 and its ligands and their therapeutic potential.

Phase I trial of sirolimus combined with radiation and cisplatin in non-small cell lung cancer

PURPOSE

The safety and tolerability of sirolimus combined with thoracic radiation and cisplatin was evaluated in patients with lung cancer. In parallel, the effects of sirolimus were studied in a murine model of radiation pneumonitis.

MATERIALS AND METHODS

The phase I trial evaluated standard three-dimensional conformal thoracic radiation therapy (60 Gy) and weekly cisplatin (25 mg/m2 i.v.) in combination with escalating doses of oral sirolimus. Sirolimus drug levels and inhibition of mTOR signaling to ribosomal S6 protein were assessed in blood. The effects of sirolimus administered during and after whole thoracic radiation of C57BL6/J mice were evaluated by monitoring mouse breathing rates and survival.

RESULTS

Seven patients with stage III lung cancer were accrued to the clinical study. None of the four patients treated with 2 mg/day sirolimus developed dose-limiting toxicities. Three patients were treated with 5 mg/day sirolimus, and one patient at this dose level had dose-limiting toxicity of grade 3 dysphagia. However, the maximally tolerated dose of sirolimus in this regimen was not defined because the study was terminated prematurely because of loss of funding. In the mouse experiments, concomitant sirolimus treatment was not associated with an increase in radiation-associated morbidity or mortality.

CONCLUSIONS

Combination therapy with sirolimus, radiation, and cisplatin was well tolerated in patients.

Fast-tracked CTL: rapid induction of potent anti-tumor killer T cells in situ

Current strategies to elicit cytolytic T cell responses specific for tumor-associated or over-expressed self antigens rely on multiple immunizations and in vitro expansion schemes. Here we report the in vivo induction of activated tumor-specific CD8(+) CTL just 6 days after treatment with the IgM immune modulator B7-DC XAb. Antibody treatment of mice at the time of tumor challenge elicited potent CTL with a specificity that distinguished between MHC-compatible tumors. Remarkably, these effector cells were not generated by the extensive proliferation of naive CTL precursors, though their induction required CD4(+) T cell help and classical B7 costimulatory signals. Tumor targets were recognized and lysed in an MHC-restricted, perforin-dependent manner, indicating that these rapidly induced effectors resemble traditionally defined CTL, despite the finding that strong increases in the expression of the effector/memory marker CD44 and the activation marker CD69 were not elicited. These CTL were induced in animals bearing well-established tumors and resulted in anti-tumor protection, underscoring the therapeutic potential of this type of effector T cell population in cancer patients.

Induction of a Th1 response from Th2-polarized T cells by activated dendritic cells: dependence on TCR:peptide-MHC interaction, ICAM-1, IL-12, and IFN-gamma

Dendritic cells (DC) are important regulators of T cell immunity. The degree of stimulation, the pattern of costimulatory molecules expressed, and the cytokines secreted by DC dictate the nature of the effector and memory cells generated, particularly with respect to their Th1 or Th2 phenotypes. In this study, we demonstrate that the addition of activated DC to spleen cultures containing established Th2-polarized CD4(+) T cells was sufficient to suppress Th2 and induce Th1 cytokines in a recall response, a phenomenon referred to as phenotype reversal. The ability of activated DC to induce phenotype reversal displayed exquisite Ag specificity. The DC activator B7-DC cross-linking Ab (XAb) was >10,000-fold more efficient at inducing phenotype reversal than the TLR agonists CpG-oligodeoxynucleotide and Gardiquimod. Characterization of the mechanisms governing phenotype reversal revealed the requirement for cognate interaction between the TCR:peptide-MHC complex, the expression of the costimulation/adhesion molecule ICAM-1, and secretion of IL-12 and IFN-gamma by the activated DC. The requirement for the costimulation/adhesion molecule SLAM (signaling lymphocytic activation molecule) was found to be quantitative. Thus, activation of DC, particularly by crosslinking B7-DC, can modulate well-established Th2 T cell responses in an Ag-specific manner. Because the regulation of mouse and human DC by B7-DC XAb overlaps in several significant ways, immune modulation with B7-DC XAb is a potential strategy for treating Th2-mediated diseases.

B7-DC/PD-L2 Cross-Linking Induces NF-κB-Dependent Protection of Dendritic Cells from Cell Death

Cross-linking cell surface molecules with IgM Abs is a specific approach for activating cells in vitro or in vivo. Dendritic cells (DC) activated with a human B7-DC (PD-L2)-specific IgM Ab can induce strong antitumor responses and block inflammatory airway disease in experimental models, yet the Ab-mediated molecular events promoting these responses remain unclear. Analysis of human or mouse DC treated with the B7-DC cross-linking Ab revealed PI3K-dependent phosphorylation of AKT accompanied by mobilization of NF-kappaB. Ab-activated DC up-regulated expression of cytokine and chemokine genes in an NF-kappaB-dependent manner. Importantly, PI3K-->AKT-->NF-kappaB activation was found to be indispensable for B7-DC cross-linking Ab-mediated protection of DC from cell death caused by cytokine withdrawal. Although other DC activators similarly protect DC from cell death, a synergy between cross-linking B7-DC and ligating RANK was observed. The parallel signaling events induced in human and mouse DC demonstrate that activation of cells using IgM Ab results in a response governed by a common mechanism and support the hypothesis that B7-DC cross-linking using this Ab may provide beneficial therapeutic immune modulation in human patients similar to those seen in animal models.

Plasmacytoid dendritic cells prime IL-10-producing T regulatory cells by inducible costimulator ligand

Although there is evidence for distinct roles of myeloid dendritic cells (DCs [mDCs]) and plasmacytoid pre-DCs (pDCs) in regulating T cell–mediated adaptive immunity, the concept of functional DC subsets has been questioned because of the lack of a molecular mechanism to explain these differences. In this study, we provide direct evidence that maturing mDCs and pDCs express different sets of molecules for T cell priming. Although both maturing mDCs and pDCs upregulate the expression of CD80 and CD86, only pDCs upregulate the expression of inducible costimulator ligand (ICOS-L) and maintain high expression levels upon differentiation into mature DCs. High ICOS-L expression endows maturing pDCs with the ability to induce the differentiation of naive CD4 T cells to produce interleukin-10 (IL-10) but not the T helper (Th)2 cytokines IL-4, -5, and -13. These IL-10–producing T cells are T regulatory cells, and their generation by ICOS-L is independent of pDC-driven Th1 and Th2 differentiation, although, in the later condition, some contribution from endogenous IL-4 cannot be completely ruled out. Thus, in contrast to mDCs, pDCs are poised to express ICOS-L upon maturation, which leads to the generation of IL-10–producing T regulatory cells. Our findings demonstrate that mDC and pDCs are intrinsically different in the expression of costimulatory molecules that drive distinct types of T cell responses.

Targeting dendritic cells in allergen immunotherapy

Allergen immunotherapy is a well-established strategy for treating allergic diseases with the goal of inducing allergen-specific tolerance. Identified mechanisms contributing to the therapeutic effect of immunotherapy include a shift of T helper 2 (Th2)-type immune responses to a modified Th2 immune response, a change of the balance of IgE-producing B cells to the production of IgG subtypes, in addition to increased IL-10 and TGF-beta secretion and activation of the suppressive functions of regulatory T-cells. Dendritic cells (DCs), which as outposts of the immune system are capable of T-cell priming through efficient allergen uptake by IgE receptors expressed on their cell surface. Most of the hypotheses concerning the function of DCs as facilitators of allergen-specific tolerance in allergen immunotherapy remain speculative. Therefore, studies must focus on the functional changes of DCs under immunotherapy to close the gap of knowledge about their exact role. These experimental data should help confirm the hypothesis of DCs as efficient silencers and potential target cells and take advantage of the bivalent character and tolerogenic properties of DCs.

Role of regulatory dendritic cells in allergy and asthma

PURPOSE OF REVIEW

Dendritic cells are the most efficient inducers of all immune responses, and are capable of inducing either productive immunity or maintaining the state of tolerance to self-antigens and allergens. The present review summarizes the emerging literature on dendritic cells, with the emphasis on regulatory function of dendritic cells in allergy and asthma. In particular we summarize recent data regarding the relationship between dendritic cell subsets and Th1, Th2 and regulatory T (TReg) cells.

RECENT FINDINGS

The diverse functions of dendritic cells have been attributed to distinct lineages of dendritic cells, which arise from common immature precursor cells that differentiate in response to specific maturation-inducing or local microenvironment conditions. These subsets induce different lineages of T cells such as Th1, Th2 and TReg cells, including Th1Reg and Th2Reg cells, which regulate allergic diseases and asthma.

SUMMARY

Subsets of dendritic cells regulate the induction of a variety of T-cell subtypes, which suppress the development of allergy and asthma, thus providing antiinflammatory responses and protective immunity.

A major lung CD103 (alphaE)-beta7 integrin-positive epithelial dendritic cell population expressing Langerin and tight junction proteins

Dendritic cells (DC) mediate airway Ag presentation and play key roles in asthma and infections. Although DC subsets are known to perform different functions, their occurrence in mouse lungs has not been clearly defined. In this study, three major lung DC populations have been found. Two of them are the myeloid and plasmacytoid DC (PDC) well-characterized in other lymphoid organs. The third and largest DC population is the integrin alpha(E) (CD103) beta(7)-positive and I-A(high)CD11c(high)-DC population. This population was found to reside in the lung mucosa and the vascular wall, express a wide variety of adhesion and costimulation molecules, endocytose avidly, present Ag efficiently, and produce IL-12. Integrin alpha(E)beta(7)(+) DC (alphaE-DC) were distinct from intraepithelial lymphocytes and distinguishable from CD11b(high) myeloid and mPDCA-1(+)B220(+)Gr-1(+) PDC populations in surface marker phenotype, cellular functions, and tissue localization. Importantly, this epithelial DC population expressed high levels of the Langerhans cell marker Langerin and the tight junction proteins Claudin-1, Claudin-7, and ZO-2. In mice with induced airway hyperresponsiveness and eosinophilia, alphaE-DC numbers were increased in lungs, and their costimulation and adhesion molecules were up-regulated. These studies show that alphaE-DC is a major and distinct lung DC population and a prime candidate APC with the requisite surface proteins for migrating across the airway epithelia for Ag and pathogen capture, transport, and presentation. They exhibit an activated phenotype in allergen-induced lung inflammation and may play significant roles in asthma pathogenesis.

Immunomodulation using the recombinant monoclonal human B7-DC cross-linking antibody rHIgM12

A patient with Waldenstrom's macroglobulinaemia expresses a high titre IgM antibody in serum that binds both mouse and human dendritic cells (DC) in a B7-DC (PD-L2)-dependent manner. We have reported previously that purified antibody from patient serum activates immature and mature DC in vitro, enhancing the ability of these professional antigen-presenting cells to activate naive T cells, take up antigen, resist a cytokine-depleted environment and secrete immunomodulatory cytokines, such as interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha. Systemic treatment of experimental animals with this antibody induces potent anti-melanoma immunity and modulates protectively the recall response against antigen challenge through the airway in an experimental model of inflammatory airway disease. Here we describe a monoclonal IgM antibody derived from this serum immunoglobulin that recapitulates each of these earlier observations, providing direct evidence that M protein from the Waldenstrom's patient mediates these potent immunomodulatory effects. Furthermore, cell lines expressing this recombinant form of the human antibody provide the basis for developing this reagent for clinical application.

Recent advances in the development of anti-allergic drugs

Research over the past decade has provided information concerning the onset and treatment of allergic diseases, including bronchial asthma, allergic rhinitis and atopic dermatitis. Recent studies also indicated that allergic inflammation is the basic pathophysiology of allergic diseases and is closely associated with their progression and exacerbation. Our understanding of the mechanism of allergic inflammation with regard to therapeutic agents has improved as a result of immunological and molecular biological studies. While much effort has been paid to developing a new anti-allergic drug, allergic disease has yet to be completely conquered. More extensive research will allow the development of new therapeutics to combat allergic diseases. This article provides an overview of recent advances in the development of anti-allergic drugs.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

B7-DC cross-linking restores antigen uptake and augments antigen-presenting cell function by matured dendritic cells

Dendritic cells (DCs) are classified in two states: immature DCs (iDCs), which perform sentinel functions, sampling for antigen and danger signals, and mature DCs (mDCs), which exhibit enhanced antigen-presenting functions but are no longer capable of acquiring antigen. We now describe DCs with a different activation phenotype: cells having the strong antigen-presenting functions of mDCs and the antigen-acquiring functions of iDCs. We have described an antibody that binds the costimulatory molecule B7-DC and activates DCs. The resulting phenotype is distinct from iDCs or mDCs matured by using Toll-like receptor (TLR) agonists. Ability to take up antigen increases, while expression of B71/2 costimulatory and MHC molecules remains unchanged. DCs matured with TLR agonists and then superactivated through B7-DC exhibit a previously unrecognized phenotype. These DCs recover the ability to take up antigen, which is normally lost after treatment with TLR-3 and TLR-9 agonists, yet retain the high expression of costimulatory and MHC molecules and strong antigen-presenting functions of mDCs. Immunization using TLR agonists and B7-DC XAb (cross-linking antibody) together as adjuvant resulted in substantially increased cytolytic T cell responses, particularly when minimal peptide antigens were used. By stimulating DCs with two distinct activation signals, a previously unrecognized phenotype exhibiting augmented antigen-presenting functions was obtained.

Modulation of Dendritic Cell Maturation and Function by B Lymphocytes

Investigating the signals that regulate the function of dendritic cells (DC), the sentinels of the immune system, is critical to understanding the role of DC in the regulation of immune responses. Accumulating lines of evidence indicate that in addition to innate stimuli and T cell-derived signals, B lymphocytes exert a profound regulatory effect in vitro and in vivo on the Ag-presenting function of DC. The identification of B cells as a cellular source of cytokines, chemokines, and autoantibodies that are critically involved in the process of maturation, migration, and function of DC provides a rationale for immunotherapeutic intervention of autoimmune and inflammatory conditions by targeting B cells. Conversely, efficient cross-presentation of Ags by DC pulsed with immune complexes provides an alternative approach in the immunotherapy of cancer and infectious diseases.

Role of regulatory dendritic cells in allergy and asthma

Dendritic cells (DCs) are the most efficient inducers of all immune responses, and are capable of either inducing productive immunity or maintaining the state of tolerance to self antigens and allergens. In this review, we summarize the emerging literature on DCs, with emphasis on the regulatory function of DCs in allergy and asthma. In particular, we summarize recent data regarding the relationship between DC subsets and TH1, TH2, and regulatory T (TReg) cells. The diverse functions of DCs have been attributed to distinct lineages of DCs, which arise from common immature precursor cells that differentiate in response to specific maturation-inducing or local microenvironment conditions. These subsets of DCs induce different lineages of T cells, such as TH1, TH2, and TReg cells, including Th1Reg and Th2Reg cells, which regulate allergic diseases and asthma. Subsets of DCs regulate the induction of a variety of T-cell subtypes, which suppress the development of allergy and asthma, thus providing anti-inflammatory responses and protective immunity.