Jeffrey M. Wilson

Brain angiogenesis inhibitor 1 (BAI1) is a pattern recognition receptor that mediates macrophage binding and engulfment of Gram-negative bacteria.

Bacterial recognition by host cells is essential for initiation of infection and the host response. Bacteria interact with host cells via multiple pattern recognition receptors that recognize microbial products or pathogen-associated molecular patterns. In response to this interaction, host cell signaling cascades are activated that lead to inflammatory responses and/or phagocytic clearance of attached bacteria. Brain angiogenesis inhibitor 1 (BAI1) is a receptor that recognizes apoptotic cells through its conserved type I thrombospondin repeats and triggers their engulfment through an ELMO1/Dock/Rac1 signaling module. Because thrombospondin repeats in other proteins have been shown to bind bacterial surface components, we hypothesized that BAI1 may also mediate the recognition and clearance of pathogenic bacteria. We found that preincubation of bacteria with recombinant soluble BAI1 ectodomain or knockdown of endogenous BAI1 in primary macrophages significantly reduced binding and internalization of the Gram-negative pathogen Salmonella typhimurium. Conversely, overexpression of BAI1 enhanced attachment and engulfment of Salmonella in macrophages and in heterologous nonphagocytic cells. Bacterial uptake is triggered by the BAI1-mediated activation of Rac through an ELMO/Dock-dependent mechanism, and inhibition of the BAI1/ELMO1 interaction prevents both Rac activation and bacterial uptake. Moreover, inhibition of ELMO1 or Rac function significantly impairs the proinflammatory response to infection. Finally, we show that BAI1 interacts with a variety of Gram-negative, but not Gram-positive, bacteria through recognition of their surface lipopolysaccharide. Together these findings identify BAI1 as a pattern recognition receptor that mediates nonopsonic phagocytosis of Gram-negative bacteria by macrophages and directly affects the host response to infection.

The A2B Adenosine Receptor Impairs the Maturation and Immunogenicity of Dendritic Cells

The endogenous purine nucleoside adenosine is an important antiinflammatory mediator that contributes to the control of CD4+ T cell responses. While adenosine clearly has direct effects on CD4+ T cells, it remains to be determined whether actions on APC such as dendritic cells (DC) are also important. In this report we characterize DC maturation and function in BMDC stimulated with LPS in the presence or absence of the nonselective adenosine receptor agonist NECA (5′-N-ethylcarboxamidoadenosine). We found that NECA inhibited TNF-α and IL-12 in a concentration-dependent manner, whereas IL-10 production was increased. NECA-treated BMDC also expressed reduced levels of MHC class II and CD86 and were less effective at stimulating CD4+ T cell proliferation and IL-2 production compared with BMDC exposed to vehicle control. Based on real-time RT-PCR, the A2A adenosine receptor (A2AAR) and A2BAR were the predominant adenosine receptors expressed in BMDC. Using adenosine receptor subtype selective antagonists and BMDC derived from A2AAR−/− and A2BAR−/−mice, it was shown that NECA modulates TNF-α, IL-12, IL-10, and CD86 responses predominantly via A2BAR. These data indicate that engagement of A2BAR modifies murine BMDC maturation and suggest that adenosine regulates CD4+ T cell responses by selecting for DC with impaired immunogencity.

The A2B Adenosine Receptor Promotes Th17 Differentiation via Stimulation of Dendritic Cell IL-6

Adenosine is an endogenous metabolite produced during hypoxia or inflammation. Previously implicated as an anti-inflammatory mediator in CD4+ T cell regulation, we report that adenosine acts via dendritic cell (DC) A2B adenosine receptor (A2BAR) to promote the development of Th17 cells. Mouse naive CD4+ T cells cocultured with DCs in the presence of adenosine or the stable adenosine mimetic 5′-(N-ethylcarboximado) adenosine resulted in the differentiation of IL-17– and IL-22–secreting cells and elevation of mRNA that encode signature Th17-associated molecules, such as IL-23R and RORγt. The observed response was similar when DCs were generated from bone marrow or isolated from small intestine lamina propria. Experiments using adenosine receptor antagonists and cells from A2BAR−/− or A2AAR−/−/A2BAR−/− mice indicated that the DC A2BAR promoted the effect. IL-6, stimulated in a cAMP-independent manner, is an important mediator in this pathway. Hence, in addition to previously noted direct effects of adenosine receptors on regulatory T cell development and function, these data indicated that adenosine also acts indirectly to modulate CD4+ T cell differentiation and suggested a mechanism for putative proinflammatory effects of A2BAR.

The Skin as a Route of Allergen Exposure: Part II. Allergens and Role of the Microbiome and Environmental Exposures

Purpose of ReviewThis second part of the article aims to highlight recent contributions in the literature that enhance our understanding of the cutaneous immune response to allergen.Recent FindingsSeveral properties of allergens facilitate barrier disruption and cutaneous sensitization. There is a strong epidemiologic relationship between the microbiome, both the gut and skin, and atopic dermatitis (AD). The mechanisms connecting these two entities remain enigmatic; however, recent murine models show that commensal skin bacteria play an active role in supporting skin barrier homeostasis and defense against microbial penetration. Likewise, the association between the lack of colonization with Staph species and AD development suggests a potentially functional role for these organisms in regulating the skin barrier and response to environmental allergens. In undisrupted skin, evidence suggests that the cutaneous route may promote allergen tolerance.SummaryProperties of environmental allergens and commensal bacteria add to the complex landscape of skin immunity. Further investigation is needed to elucidate how these properties regulate the cutaneous immune response to allergen.

Home Environmental Interventions for House Dust Mite

It has been 50 years since the dust mite was first appreciated to be a major source of allergen in house dust, and by extension a key trigger of allergic respiratory disease. Since that time a number of protein allergens have been identified and characterized, mainly from mite feces, and standardized mite extracts and IgE assays have been developed. Insights into the lifecycle of dust mites and aspects of mite allergen biology have shed light on the mechanisms that lead to respiratory disease and to the development of interventions that can minimize dust mite allergen exposure. It is now clear that dust mite allergy is a key contributor to asthma in many parts of the world, and that long-term avoidance can be effective for preventing sensitization and minimizing the development and severity of respiratory disease. Here, we discuss the evidence linking dust mites with respiratory disease, outline studies that support the efficacy of home environmental interventions, and highlight practical methods that have been shown to be effective as part of a multifaceted approach to dust mite avoidance.

The Skin as a Route of Allergen Exposure: Part I. Immune Components and Mechanisms

Purpose of ReviewTo highlight recent contributions in the literature that enhance our understanding of the cutaneous immune response to allergen.Recent FindingsDefects in skin barrier function in infancy set the stage for the development of atopic dermatitis (AD) and allergy. Both genetic and environmental factors can contribute to damage of the stratum corneum (SC), with activation of specific protease enzymes under high pH conditions playing a key role. Immune cells and mediators in the dermis and epidermis impair SC repair mechanisms and support allergy development. In barrier-disrupted skin, type 2 innate lymphoid cells (ILC2s), mast cells (MCs), and basophils have been shown to promote AD and pathogenic Th2 responses in murine models.SummarySkin barrier disruption favors induction of systemic Th2-associated inflammatory pathways. A better understanding of the ontogeny and regulation of these complex networks in infant skin is needed to guide future strategies for allergy treatment and prevention.

Specific IgG4 Antibodies to Cow’s Milk Proteins in Pediatric Eosinophilic Esophagitis

Background: Allergen‐specific IgG4 (sIgG4) antibodies are often associated with tolerance, but sIgG4 antibodies to causally relevant foods have been reported recently in adults with eosinophilic esophagitis (EoE). Prevalence and levels of food sIgG4 are not well established in the general pediatric population. Objective: We sought to investigate serum food sIgG4 with component diagnostics in children with EoE and children from an unselected birth cohort and to explore the effects of sex, age, and milk consumption on sIgG4 levels. Methods: Sera from 71 pediatric patients with EoE and 210 early adolescent children from an unselected birth cohort (Project Viva) were assayed for sIgG4 and specific IgE (sIgE) to major cows milk (CM) proteins (&agr;‐lactalbumin, &bgr;‐lactoglobulin, and caseins) and to wheat, soy, egg, and peanut proteins. Results: In the EoE cohort high‐titer sIgG4 (≥10 &mgr;g/mL) to CM proteins was more common than in control sera and achieved odds ratios for EoE ranging from 5.5 to 8.4. sIgE levels to CM proteins were mostly 4 IU/mL or less in patients with EoE, such that sIgG4/sIgE ratios were often 10,000 or greater. When adjusted for age and milk consumption, high‐titer sIgG4 to CM proteins was strongly associated with EoE, with an odds ratio of greater than 20 to all 3 CM proteins in boys. Conclusions: sIgG4 to CM proteins are common and high titer in children with EoE. Although it is not clear that this response is pathogenic, sIgG4 levels imply that these antibodies are an important feature of the local immune response that gives rise to EoE. GRAPHICAL ABSTRACT Figure. No caption available.

Meat allergy and allergens

HighlightsMeat, particularly from mammalian sources, is increasingly appreciated as an important food allergen.Many forms of meat allergy involve molecular allergens that are shared across several related species.The oligosaccharide galactose &agr;‐1,3‐galactose (&agr;‐Gal) is an important cause of delayed anaphylaxis to mammalian meat.There are several meat allergy syndromes where the mechanism of sensitization is unrelated to oral exposure.IgE component testing has an important role to play in diagnosis and management of meat allergy. ABSTRACT IgE‐mediated hypersensitivity to ingested animal products, including both mammalian and avian sources, is increasingly appreciated as an important form of food allergy. Traditionally described largely in children, it is now clear that allergy to meat (and animal viscera) impacts both children and adults and represents a heterogeneous group of allergic disorders with multiple distinct syndromes. The recognition of entities such as pork‐cat syndrome and delayed anaphylaxis to red meat, i.e‐ the &agr;‐Gal syndrome, have shed light on fundamental, and in some cases newly appreciated, features of allergic disease. These include insights into routes of exposure and mechanisms of sensitization, as well as the realization that IgE‐mediated reactions can be delayed by several hours. Here we review mammalian and avian meat allergy with an emphasis on the molecular allergens and pathways that contribute to disease, as well as the role of in vitro IgE testing in diagnosis and management.

Diagnosis and Management of Eosinophilic Esophagitis

Unlike traditional food allergies, immunoglobulin E (IgE) is not a key mediator of eosinophilic esophagitis (EoE). Nonetheless, foods antigens are important triggers of EoE, and allergists play an important role in management of this chronic disease. This review addresses insights into the diagnosis and management as it relates to our evolving understanding about the pathogenesis of EoE.

Underestimation of specific IgE measurements using extract-based assays on undiluted sera revealed through dilution

The measurement of specific IgE (sIgE) to foods is an established clinical tool for the diagnosis and management of allergic disease. Normally, sIgE is measured using undiluted serum, and assays are only performed at a dilution if the value is greater than or equal to 90 international units (IU)/mL. Thus, when serum gives sIgE values of less than or equal to 50 IU/mL, the possibility that the value is a significant underestimate is rarely considered. The underestimation of results using undiluted serum is a well-known limitation of immunoprecipitation, immunodiffusion, and nephelometry, where it is referred to as a “prozone” or “hook” effect. However, there is very little awareness of this phenomenon in the measurement of sIgE. We sought to investigate this phenomenon using sera collected from patients with the a-gal syndrome (AS) (n 1⁄4 3), which involves delayed reactions to mammalian products (red meat or dairy) related to sIgE to galactose-a-1,3-galactose (a-gal). We addressed additional allergens using sera from subjects with eosinophilic esophagitis (EoE) (n 1⁄4 17), peanut allergy (n 1⁄4 4), or oral allergy syndrome (n 1⁄4 5). Serum was collected from patients at the University of Virginia (Charlottesville, Va) or Ohio State University/Nationwide Children’s Hospital (Columbus, Ohio) clinics. We measured sIgE to beef, milk, mite (Dermatophagoides pteronyssinus), cat dander, cow’s milk, and peanut extracts by ImmunoCAP in progressively diluted sera. The results were expressed in fluorescent response units (FRU) or IU/mL (positive, 0.35 IU/mL). In addition, sIgE to purified allergens was measured by ImmunoCAP (a-gal, Bos d 4, Bos d 5, Bos d 6, Bos d 8, Ara h 1, Ara h 2, and/or Ara h 8) or Immuno Solid-Phase Allergen Chip (Der p 1, Der p 2, Der p 10, Fel d 1, and/or Fel d 4) to determine the patients’ dominant sensitization(s). Methods for sIgE to a-gal, Immuno Solid-Phase Allergen Chip, and IgG4 assays are detailed in this article’s Online Repository at www.jaci-inpractice.org. In brief, the a-gal sIgE assay uses 20 mg cetuximab coupled to the solid phase. The result in Figure 1, A, demonstrates that there is a substantial dilution effect when assaying sIgE to beef and milk extract in sera from a subject with AS. Of note, a-gal constitutes a minor fraction of the antigens in beef and milk. To further examine this phenomena, we performed dilution studies using ImmunoCAP for beef extract or a-gal on sera from 3 patients with AS who had highly positive sIgE to a-gal (>100 IU/mL). These values for sIgE to a-gal allowed us to dilute the sera past 1:1000 before sIgE levels were undetectable. We compared curves for sIgE to beef extract and a-gal to a control curve, which revealed dramatic differences (Figure 1, B and C). Focusing on sIgE to beef extract in AS #1, the FRU in the undiluted serum were approximately the same as the value for the 1:4 dilution, which illustrated a “hook” effect (Figure 1, C). In another patient with AS who was highly positive for sIgE to a-gal (>100 IU/mL), we recreated the situation of insufficient antigen using progressively diluted serum and low cetuximab (800 ng) on the solid phase (see Figure E1 in this article’s Online Repository at www.jaci-inpractice.org). The dilution curve deviated from the control curve and that of the standard cetuximab immunoCAP, indicating that the amount of antigen on the solid phase was insufficient for accurate measurement of sIgE to a-gal. We also applied decreasing quantities of cetuximab to the solid phase and measured sIgE to a-gal using undiluted serum from a patient with AS (see Figure E2 in this article’s Online Repository at www.jaci-inpractice.org) and the resultant curve showed a dose-response relationship between the mass of cetuximab on the solid phase and the assay readout. Thus, manipulating the amount of allergen on the solid phase, such that there is an imbalance in antibody and allergen concentrations, can markedly change the measured sIgE values. Next, we performed dilution studies using sIgE assays for mite (n 1⁄4 6), cat dander (n 1⁄4 4), and cow’s milk (n 1⁄4 11) extracts in selected IgE-positive sera from 17 patients with EoE and also for peanut extract in the sera from patients with peanut allergy and oral allergy syndrome. Mite, cat dander, cow’s milk, and peanut extracts consist of many different allergens, which are present in unequal amounts on the solid phase (see Table E1 in this article’s Online Repository at www.jaci-inpractice.org). In cases in which Der p 2, Fel d 1, Bos d 8, or Ara h 2 were the primary allergen targets, dilution had little effect on the results; each of these allergens represents a significant or large proportion of the respective extracts (Figure 1, D). In contrast, there was a pronounced dilution effect in many of the sera from subjects dominantly sensitized to Bos d 4 and Ara h 8, which are quantitatively a minor fraction of the relevant extract (Figure 1, D; Table E1). We then determined the percentage difference in sIgE values in the undiluted and 1:8 (calculated) samples from each assay (Table I). There was a strong negative correlation (rs 1⁄4 0.79; 95% CI, 0.90 to 0.61; P < .001) between the representation of the dominant allergen for each patient and the percentage difference between the undiluted and 1:8 measurements (Figure 1, E; see Table E2 in this article’s Online Repository at www.jaci-inpractice.org). There are 2 major effects related to the use of undiluted serum in sIgE assays that can cause false negatives or that can underestimate measurements. Both effects essentially occur because of