Kristin L. Chichester

TLR9- and FcεRI-Mediated Responses Oppose One Another in Plasmacytoid Dendritic Cells by Down-Regulating Receptor Expression

Plasmacytoid dendritic cells (pDC) express not only TLR9 molecules through which ligation with CpG DNA favors Th1 responses but also possess IgE receptors (FcεRI) implicated in allergen presentation and induction of Th2 responses. This dichotomy prompted an investigation to determine whether TLR9- and IgE receptor-mediated responses oppose one another in pDC by affecting receptor expression and associated functional responses. Results showed that IgE cross-linking reduced TLR9 in pDC and inhibited the capacity of these cells to secrete IFN-α when stimulated with the CpG oligodeoxynucleotide (ODN)-2216. In contrast, an ∼15-fold reduction in FcεRIα mRNA and a loss in surface protein were seen in pDC first exposed to TLR9 ligation with ODN-2216. Results indicated that type I IFNs partly mediated this effect, as rIFN-α also caused a significant ∼4-fold reduction in FcεRIα mRNA. Finally, this reduction in FcεRIα mediated by ODN-2216 correlated with a selective suppression of allergen-induced CD4+ T cell proliferation, but not of responses resulting from tetanus toxoid. Overall, these results imply mechanisms by which specific innate and IgE-dependent immune responses counterregulate one another at the dendritic cell level and may have significant impact on whether an ensuing response is either of Th1 or Th2 in nature.

Human blood dendritic cells from allergic subjects have impaired capacity to produce interferon‐α via toll‐like receptor 9

Background High‐affinity IgE receptor (FcɛRI) expression on blood dendritic cells reportedly correlates with serum IgE levels. Our studies demonstrate that plasmacytoid dendritic cells (pDCs) secrete pro‐inflammatory cytokines (IL‐6, TNF‐α) following FcɛRI stimulation – a mode of activation that simultaneously reduces expression of Toll‐like receptor 9 (TLR9). Whether or not TLR9 and/or FcɛRI levels and their function on dendritic cells relate to allergic status is unknown.

Human Basophils Secrete IL-3: Evidence of Autocrine Priming for Phenotypic and Functional Responses in Allergic Disease

Although IL-3 is commonly recognized for its growth factor-like activity, in vitro studies have long demonstrated a unique capacity for this cytokine to also augment the proinflammatory properties and phenotype of human basophils. In particular, basophils secrete mediators that are hallmarks in allergic disease, including vasoactive amines (e.g., histamine), lipid metabolites (e.g., leukotriene C4), and cytokines (e.g., IL-4/IL-13), which are all markedly enhanced with IL-3 pretreatment. This priming phenomenon is observed in response to both IgE-dependent and IgE-independent stimulation. Additionally, IL-3 directly activates basophils for IL-13 secretion and enhanced CD69 expression, two markers that are elevated in allergic subjects. Lymphocytes are commonly thought to be the source of the IL-3 that primes for these basophil responses. However, we demonstrate herein for the first time that basophils themselves rapidly produce IL-3 (within 4 h) in response to IgE-dependent activation. More importantly, our findings definitively show that basophils rapidly bind and utilize the IL-3 they produce, as evidenced by functional and phenotypic activity that is inhibited in the presence of neutralizing anti-IL-3 receptor (CD123) Abs. We predict that autocrine IL-3 activity resulting from low-level IgE/FcεRI cross-linking by specific allergen represents an important mechanism behind the hyperreactive nature of basophils that has long been observed in allergic disease.

TGFβ Receptor Mutations Impose a Strong Predisposition for Human Allergic Disease

Patients with mutations in the receptors for TGFβ (Loeys-Dietz syndrome) exhibit an increased prevalence of allergic diseases. Allergy Unveiled Loeys-Dietz syndrome (LDS) is an autosomal dominant disorder closely related to Marfan syndrome caused by mutations in the genes encoding receptor subunits for transforming growth factor–β (TGFβ). Patients with LDS are predisposed to aortic aneurisms and other connective tissue disorders. Now, Frischmeyer-Guerrerio et al. report that patients with LDS are more likely to develop allergic diseases. Allergy occurs when the immune system responds to normally harmless substances. The authors observed that LDS patients had elevated incidence of allergic diseases, including asthma, food allergy, eczema, allergic rhinitis, and eosinophilic gastrointestinal disease. These patients had elevated levels of immune responses thought to contribute to allergy, including allergen-specific IgE, eosinophilia, and TH2 cytokines. Because regulatory T cell (Treg) development is regulated by TGFβ, the authors then examined Treg number and function in these patients. They found that the frequency of Tregs was increased in LDS patients, but that these cells produced TH2 effector cytokines, and in vitro studies suggested that LDS mutations promote TH2 inflammation. What’s more, children with allergic disease, but not LDS, had similar changes in Treg number and function. These data suggest that altered TGFβ signaling could promote allergic disease and support testing for U.S. Food and Drug Administration–approved drugs that affect TGFβ for treating allergy. Transforming growth factor–β (TGFβ) is a multifunctional cytokine that plays diverse roles in physiologic processes as well as human disease, including cancer, heart disease, and fibrotic disorders. In the immune system, TGFβ regulates regulatory T cell (Treg) maturation and immune homeostasis. Although genetic manipulation of the TGFβ pathway modulates immune tolerance in mouse models, the contribution of this pathway to human allergic phenotypes is not well understood. We demonstrate that patients with Loeys-Dietz syndrome (LDS), an autosomal dominant disorder caused by mutations in the genes encoding receptor subunits for TGFβ, TGFBR1 and TGFBR2, are strongly predisposed to develop allergic disease, including asthma, food allergy, eczema, allergic rhinitis, and eosinophilic gastrointestinal disease. LDS patients exhibited elevated immunoglobulin E levels, eosinophil counts, and T helper 2 (TH2) cytokines in their plasma. They had an increased frequency of CD4+ T cells that expressed both Foxp3 and interleukin-13, but retained the ability to suppress effector T cell proliferation. TH2 cytokine–producing cells accumulated in cultures of naïve CD4+ T cells from LDS subjects, but not controls, after stimulation with TGFβ, suggesting that LDS mutations support TH2 skewing in naïve lymphocytes in a cell-autonomous manner. The monogenic nature of LDS demonstrates that altered TGFβ signaling can predispose to allergic phenotypes in humans and underscores a prominent role for TGFβ in directing immune responses to antigens present in the environment and foods. This paradigm may be relevant to nonsyndromic presentations of allergic disease and highlights the potential therapeutic benefit of strategies that inhibit TGFβ signaling.

Upregulation of FcϵRI on human basophils by IgE antibody is mediated by interaction of IgE with FcϵRI

Abstract Background: IgE is now known to upregulate the expression of FcϵRI on human basophils. It is not known which receptor on basophils mediates this process of upregulation. Objective: We sought to determine whether galectin-3, FcϵRII (CD23), or FcϵRI were involved in the upregulation of FcϵRI by IgE. Methods: The role of galectin-3 was examined by measuring the influence of α-lactose on upregulation. Basophils were examined for expression of FcϵRII (CD23) by flow cytometry and messenger (m)RNA expression. Functional discrimination between binding to FcϵRII or FcϵRI was examined through the use of mutant IgE-Fc fragments or anti-FcϵRII antibody. Results: Upregulation of FcϵRI on basophils in the presence of IgE was not altered by coincubation with α-lactose, eliminating a role for galectin-3. Basophils were not found to express FcϵRII, as determined by flow cytometry with enriched basophil preparations or RT-PCR with highly purified basophil preparations. A mutant of the Fc fragment of IgE (IgE-Fc), which binds to FcϵRI with a greater than 10-fold lower affinity than IgE or wild-type IgE-Fc but exhibits no change in affinity for FcϵRII, allowed us to distinguish between the functions of the two Fc receptors. The mutant (R334S; Henry et al 1997) was required at about 30-fold higher concentration than the wild-type IgE-Fc for the same stimulation of FcϵRI expression on basophils, thus excluding a role for FcϵRII in the response. In addition, treatment of basophils with anti-FcϵRII antibody (MHM6), which is known to be competitive with IgE, had no effect on the expression of FcϵRI or the ability of IgE to upregulate expression of FcϵRI. Conclusion: Collectively, these data indicate that IgE interacts with FcϵRI to upregulate its expression on human basophils. (J Allergy Clin Immunol 1999;104:492-8.)

Decreases in human dendritic cell–dependent TH2-like responses after acute in vivo IgE neutralization

BACKGROUND Dendritic cells (DCs) and other professional antigen-presenting cells express a variant of the high-affinity IgE receptor known as alphagamma(2), which, on the basis of in vitro findings, has long been implicated to function in facilitating allergen uptake and presentation to T(H) cells. OBJECTIVES To use omalizumab as an in vivo tool to neutralize IgE binding to circulating dendritic cells and to assess whether this results in altered DC-dependent T-cell responsiveness to allergen ex vivo. METHODS Subjects with cat allergy were enrolled in a 3.5-month, double blind, randomized (3.5:1), placebo-controlled trial of omalizumab using standard dosing for allergic asthma. Blood plasmacytoid and myeloid DCs were assessed at baseline and posttreatment for expression of surface IgE, FcepsilonRIalpha, and induction of CD4(+)T-cell proliferation and cytokine responses to cat allergen. RESULTS IgE expression on plasmacytoid and myeloid DCs from omalizumab-treated subjects (n = 12) decreased by > or =95% posttreatment (P = .0005), whereas FcepsilonRIalpha expression decreased by 66% and 48%, respectively (P = .0005). Cat allergen-induced proliferation in DC/T-cell cocultures observed at baseline was suppressed approximately 20% to 40% postomalizumab treatment (P = .001). Multiplexing for cytokines in plasmacytoid DC/T-cell cocultures also showed decreases in IL-5, IL-13, and IL-10 (P < .05), whereas IL-2 and IFN-gamma were unaltered or slightly increased. These changes were not evident in placebo-control subjects (n = 4). CONCLUSION IgE likely facilitates allergen presentation by dendritic cells in vivo and is also important in regulating DC-dependent T-cell cytokines during effector phases of allergic disease.

Suppression of the immunologic response to peanut during immunotherapy is often transient

BACKGROUND Studies suggest that oral immunotherapy (OIT) and sublingual immunotherapy (SLIT) for food allergy hold promise; however, the immunologic mechanisms underlying these therapies are not well understood. OBJECTIVE We sought to generate insights into the mechanisms and duration of suppression of immune responses to peanut during immunotherapy. METHODS Blood was obtained from subjects at baseline and at multiple time points during a placebo-controlled trial of peanut OIT and SLIT. Immunologic outcomes included measurement of spontaneous and stimulated basophil activity by using automated fluorometry (histamine) and flow cytometry (activation markers and IL-4), measurement of allergen-induced cytokine expression in dendritic cell (DC)-T-cell cocultures by using multiplexing technology, and measurement of MHC II and costimulatory molecule expression on DCs by using flow cytometry. RESULTS Spontaneous and allergen-induced basophil reactivity (histamine release, CD63 expression, and IL-4 production) were suppressed during dose escalation and after 6 months of maintenance dosing. Peanut- and dust mite-induced expression of TH2 cytokines was reduced in DC-T-cell cocultures during immunotherapy. This was associated with decreased levels of CD40, HLA-DR, and CD86 expression on DCs and increased expression of CD80. These effects were most striking in myeloid DC-T-cell cocultures from subjects receiving OIT. Many markers of immunologic suppression reversed after withdrawal from immunotherapy and in some cases during ongoing maintenance therapy. CONCLUSION OIT and SLIT for peanut allergy induce rapid suppression of basophil effector functions, DC activation, and TH2 cytokine responses during the initial phases of immunotherapy in an antigen-nonspecific manner. Although there was some interindividual variation, in many patients suppression appeared to be temporary.

Subcutaneous allergen immunotherapy restores human dendritic cell innate immune function.

Background We recently reported that human blood dendritic cells from allergic subjects have impaired IFN‐α production following toll‐like receptor 9 (TLR9)‐dependent innate immune stimulation. It is not known how subcutaneous allergen immunotherapy (SCIT) affects dendritic cell immune responses.

Dendritic Cell and T cell Responses in Children with Food Allergy

Background Food allergy (FA) and eosinophilic oesophagitis (EE) are increasingly common clinical problems. Dendritic cells (DCs) are key regulators of the sensitization and effector phases of allergic immune responses, but their role in these diseases is largely unknown.

Histamine-releasing factor/translationally controlled tumor protein (HRF/TCTP)-induced histamine release is enhanced with SHIP-1 knockdown in cultured human mast cell and basophil models

Previously, we demonstrated a negative correlation between histamine release to histamine‐releasing factor/translationally controlled tumor protein (HRF/TCTP) and protein levels of SHIP‐1 in human basophils. The present study was conducted to investigate whether suppressing SHIP‐1 using small interfering (si)RNA technology would alter the releasability of culture‐derived mast cells and basophils, as determined by HRF/TCTP histamine release. Frozen CD34+ cells were obtained from the Fred Hutchinson Cancer Research Center (Seattle, WA, USA). Cells were grown in StemPro‐34 medium containing cytokines: mast cells with IL‐6 and stem cell factor (100 ng/ml each) for 6–8 weeks and basophils with IL‐3 (6.7 ng/ml) for 2–3 weeks. siRNA transfections were performed during Week 6 for mast cells and Week 2 for basophils with siRNA for SHIP‐1 or a negative control siRNA. Changes in SHIP‐1 expression were determined by Western blot. The functional knockdown was measured by HRF/TCTP‐induced histamine release. siRNA knockdown of SHIP‐1 in mast cells ranged from 31% to 82%, mean 65 ± 12%, compared with control (n=4). Histamine release to HRF/TCTP was increased only slightly in two experiments. SHIP‐1 knockdown in basophils ranged from 34% to 69%, mean 51.8 ± 7% (n=4). Histamine release to HRF/TCTP in these basophils was dependent on the amount of SHIP knockdown. Mast cells and basophils derived from CD34+ precursor cells represent suitable models for transfection studies. Reducing SHIP‐1 protein in cultured mast cells and in cultured basophils increases releasability of the cells.