IgE versus IgG and IgA: Differential roles of allergen-specific antibodies in sensitization, tolerization, and treatment of allergies.

The prevalence of asthma, rhinitis, and food allergies has increased dramatically over the last few decades. This increase originally started in western countries, but is now also evident in many other regions of the world. Given the fact that the increase is so quick, the noted increase cannot be linked to a genetic effect, and many environmental factors have been identified that are associated with increased or reduced prevalence of allergies, like changing dietary habits, increased urbanization, pollution, exposure to microorganisms and LPS, and the farming environment and raw milk consumption. Although the key role of allergen-specific IgE in allergies is well known, the role of allergen-specific IgG and IgA antibodies is less well defined. This review will provide an overview of the functions of allergen-specific IgE in allergy, the role of allergen-specific antibodies (IgG (4) and IgA) in allergen immunotherapy (AIT), the possibility to use allergen-specific antibodies for treatment of ongoing allergies, and the potential role of allergen-specific antibodies in tolerance induction to allergens in a preventive setting. In the last, more speculative, section we will present novel hypotheses on the potential role of allergen-specific non-IgE antibodies in allergies by directing antigen presentation, Th2 development, and innate immune training.

House dust mite-specific IgA2 is associated with protection against eczema in allergic patients.

Upon inhalation, house dust mite (HDM) allergens are deposited at the nasal and oral mucosa, where IgA is produced abundantly. IgA subclasses have been linked to protection against respiratory allergy previously. It is currently not known whether and how the human IgA subclasses IgA1 and IgA2 contribute to the clinical status of house dust mite-allergic patients. Saliva and serum samples were collected, and HDM-specific, IgE, IgG4, IgA1 and IgA2 levels were determined. HDM-specific levels of IgA in serum were similar to levels measured in nonallergic controls, but HDM-specific levels of IgA2 in saliva were decreased in allergic subjects. HDM-allergic patients who suffered from rhinitis and eczema showed a significant decrease in IgA2-levels compared to patients who suffered from rhinitis only. Taken together, our findings indicate that HDM-specific IgA2, but not IgA1, levels in serum and saliva are reduced in HDM-allergic patients suffering from eczema.

Immunomodulating properties of protein hydrolysates for application in cow's milk allergy.

Cow's milk proteins cause allergic symptoms in 2-3% of all infants. In these individuals, the tolerogenic state of the intestinal immune system is broken, which can lead to sensitization against antigens and eventually to allergic responses. Although a true treatment for food allergy is not available, symptoms can be avoided by providing the infants with hydrolyzed proteins. Hydrolyzed proteins are proteins that are enzymatically degraded. They lack typical allergenic IgE-binding epitopes but are also thought to play a pertinent role in other mechanisms inducing hypoallergenic effects. This review discusses the mechanisms and evidence for immunomodulating properties of cow's milk hydrolysates. Hydrolysates are found to strengthen the epithelial barrier, modulate T-cell differentiation, and decrease inflammation. Some studies suggest a role for hydrolysates in manipulating pathogen recognition receptors signaling as underlying mechanism. Peptides from hydrolysates have been shown to bind to TLR2 and TLR4 and influence cytokine production in epithelial cells and macrophages. Current insight suggests that hydrolysates may actively participate in modulating the immune responses in subjects with cow's milk allergy and those at risk to develop cow's milk allergy. However, more research is required to design effective and reproducible means to develop targeting strategies to modulate the immune response.

Recent developments in basophil research: do basophils initiate and perpetuate type 2 T-helper cell responses?.

Basophils account for only 0.1-1% of all peripheral blood leukocytes. They were considered to be a redundant cell type for a long time. However, several findings show a non-redundant role for basophils in type 2 T-helper cell (Th2) immune responses in helminth infections, allergy and autoimmunity. Both immunoglobulin-E-dependent and -independent pathways have been described to contribute to basophil activation. In addition, several recent studies reported that basophils can function as antigen-presenting cells and are important in the initiation of Th2 immune responses. However, there are also conflicting studies that do not corroborate the importance of basophils in Th2 immune responses. This review discusses the role of basophils in Th2 immune responses in view of these recent findings.

A consideration of biomarkers to be used for evaluation of inflammation in human nutritional studies.

To monitor inflammation in a meaningful way, the markers used must be valid: they must reflect the inflammatory process under study and they must be predictive of future health status. In 2009, the Nutrition and Immunity Task Force of the International Life Sciences Institute, European Branch, organized an expert group to attempt to identify robust and predictive markers, or patterns or clusters of markers, which can be used to assess inflammation in human nutrition studies in the general population. Inflammation is a normal process and there are a number of cells and mediators involved. These markers are involved in, or are produced as a result of, the inflammatory process irrespective of its trigger and its location and are common to all inflammatory situations. Currently, there is no consensus as to which markers of inflammation best represent low-grade inflammation or differentiate between acute and chronic inflammation or between the various phases of inflammatory responses. There are a number of modifying factors that affect the concentration of an inflammatory marker at a given time, including age, diet and body fatness, among others. Measuring the concentration of inflammatory markers in the bloodstream under basal conditions is probably less informative compared with data related to the concentration change in response to a challenge. A number of inflammatory challenges have been described. However, many of these challenges are poorly standardised. Patterns and clusters may be important as robust biomarkers of inflammation. Therefore, it is likely that a combination of multiple inflammatory markers and integrated readouts based upon kinetic analysis following defined challenges will be the most informative biomarker of inflammation.

Short-chain fatty acids inhibit the activation of T lymphocytes and myeloid cells and induce innate immune tolerance.

The intestinal microbiota contributes to gut immune homeostasis, where short-chain fatty acids (SCFAs) function as the major mediators. We aimed to elucidate the immunomodulatory effects of acetate, propionate, and butyrate. With that in mind, we sought to characterise the expression of SCFA receptors and transporters as well as SCFAs' impact on the activation of different immune cells. Whereas all three SCFAs decreased tumour necrosis factor (TNF)-α production in activated T cells, only butyrate and propionate inhibited interferon (IFN)-γ, interleukin (IL)-17, IL-13, and IL-10 production. Butyrate and propionate inhibited the expression of the chemokine receptors CCR9 and CCR10 in activated T- and B-cells, respectively. Similarly, butyrate and propionate were effective inhibitors of IL-1ß, IL-6, TNF-α, and IL-10 production in myeloid cells upon lipopolysaccharide and R848 stimulation. Acetate was less efficient at inhibiting cytokine production except for IFN-α. Moreover, SCFAs inhibited the production of IL-6 and TNF-α in monocytes, myeloid dendritic cells (mDC), and plasmacytoid dendritic cells (pDC), whereas acetate effects were relatively more prominent in pDCs. In monocytes and mDCs, acetate was a less efficient inhibitor, but it was equally effective in inhibiting pDCs activation. We also studied the ability of SCFAs to induce trained immunity or tolerance. Butyrate and propionate - but not acetate - prevented Toll-like receptor-mediated activation in SCFA-trained cells, as demonstrated by a reduced production of IL-6 and TNF-α. Our findings indicate that butyrate and propionate are equally efficient in inhibiting the adaptive and innate immune response and did not induce trained immunity. The findings may be explained by differential SCFA receptor and transporter expression profiles of the immune cells.

Oral cholera vaccination promotes homing of IgA+ memory B cells to the large intestine and the respiratory tract.

Oral cholera vaccination is used to induce immune responses in the intestines to protect against cholera infection. However, oral vaccination may also affect immune responses in other mucosal tissues. To study this, tissue-specific homing potential and kinetics of B-cell responses were characterized after oral cholera vaccination. Healthy adult volunteers received two doses of Dukoral® and blood, saliva, nasal wash, and fecal samples were collected over time to detect vaccine-specific antibodies. Additionally, homing potential of lymphocytes to small intestine, colon, airways, skin, and periphery was measured by expression of Integrin ß1 and ß7, CCR9, CCR10, CCR7, and CLA. After vaccination, antibody responses to cholera toxin B (CTB) and Dukoral® were detected in serum and nasal wash. CTB-specific memory B cells in peripheral blood and tissue homing profiles of memory B cells peaked at day 18. IgA+ memory B cells expressed markers that enable homing to the airways and colon, while IgA- memory B cells primarily expressed small-intestine-homing markers. These data show that oral cholera vaccination has a differential effect on immune responses in various mucosal sites, including the respiratory tract.

A proteomics-based identification of putative biomarkers for disease in bovine milk.

The objective of this study was to identify and characterize potential biomarkers for disease resistance in bovine milk that can be used to indicate dairy cows at risk to develop future health problems. We selected high- and low-resistant cows i.e. cows that were less or more prone to develop diseases according to farmers' experience and notifications in the disease registration data. The protein composition of milk serum samples of these high- and low-resistant cows were compared using NanoLC-MS/MS. In total 78 proteins were identified and quantified of which 13 were significantly more abundant in low-resistant cows than high-resistant cows. Quantification of one of these proteins, lactoferrin (LF), by ELISA in a new and much larger set of full fat milk samples confirmed higher LF levels in low- versus high-resistant cows. These high- and low-resistant cows were selected based on comprehensive disease registration and milk recording data, and absence of disease for at least 4 weeks. Relating the experienced diseases to LF levels in milk showed that lameness was associated with higher LF levels in milk. Analysis of the prognostic value of LF showed that low-resistant cows with higher LF levels in milk had a higher risk of being culled within one year after testing than high-resistant cows. In conclusion, LF in milk are higher in low-resistant cows, are associated with lameness and may be a prognostic marker for risk of premature culling.

Late rather than early responses of human dendritic cells highlight selective induction of cytokines, chemokines and growth factors by probiotic bacteria.

The probiotic properties of commensal bacteria including lactobacilli and bifidobacteria are likely to be determined at least in part by their effects on dendritic cells. Like traditional immune stimulants such as lipopolysaccharides (LPS), probiotic bacteria promote maturation of cultured human dendritic cells (DC) by inducing elevated expression of MHC-II and co-stimulatory molecules. Different effects have been reported on cytokine induction, especially of major regulatory cytokines such as TNF-α, IL-12 and IL-10. Yet, these previous analyses have failed to reveal consistent differences between such effects of probiotics on the one hand, and of LPS on the other. Selective response markers for probiotics, however, would be important for our understanding of their biological properties and for a rational selection of strains for in vivo studies. In this study, we compared in detail both early and late effects on cultured human DC of 4 different probiotics with those of LPS. At the early stages of stimulation, all stimuli induced qualitatively very similar responses in DC at the level of surface markers and secretion of cytokines and chemokines. A lower immune stimulatory effect was observed by Bifidobacterium animalis BB-12 as compared to lactobacilli. Late responses, on the other hand, tended to diverge. Microarray transcript profiling for 268 cytokines, chemokines, growth factors and their receptors after 2 days of culture revealed various transcripts to be selectively induced by certain probiotics but not LPS. Our data indicate that late rather than early DC responses may be helpful to clarify the divergent biological effects of probiotics on human innate immune responses.

Maintenance of tolerance to cow's milk in atopic individuals is characterized by high levels of specific immunoglobulin G4.

BACKGROUND: The central role of specific IgE in cow's milk allergy (CMA) is well documented. However, less is known about the function of other immunoglobulin isotypes in allergy and tolerance to cow's milk proteins (CMPs). OBJECTIVE: To determine differences in the antibody responses that are associated with allergy and tolerance to cow's milk in allergic, atopic and non-atopic individuals of different age groups. METHODS: Nineteen infants (<1 year), 18 children (6-14 years) and 41 adults (21-68 years) were included. Each age group was comprised of subjects with CMA, atopic individuals without a history of CMA and non-atopic subjects. Levels of specific IgE, IgG4, IgG1 and IgA to whole cow's milk and the six most abundant individual CMPs were determined in plasma by ELISA. For comparison, specific IgE and IgG4 were measured to ovomucoid and house dust mite (HDM) in individuals allergic for the respective allergens, and in atopic and non-atopic subjects without allergy. RESULTS: In infants and children with CMA, alphas1-casein and beta-lactoglobulin induced the highest specific IgE response, whereas alphas1-casein was the most allergenic CMP in adult patients. Specific IgG4 and IgG1 responses were the highest to alphas1-casein and beta-lactoglobulin in all age groups, while kappa-casein and alpha-lactalbumin induced the highest levels of IgA. CMP-specific IgG4 was higher in atopic children and adults without CMA, as compared with non-atopic individuals. A similar difference between tolerant atopic and non-atopic subjects was observed for IgG4 specific to ovomucoid, whereas HDM-specific IgG4 was not detectable in these subjects. CONCLUSION: Maintenance of tolerance to cow's milk in atopic children and adults without CMA is associated with elevated levels of specific IgG4, in combination with low specific IgE. The up-regulation of specific IgG4 in tolerant atopic individuals may be related to the type of allergen and its regular dose of exposure.

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

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

A double-blind, placebo-controlled birch allergy vaccination study: inhibition of CD23-mediated serum-immunoglobulin E-facilitated allergen presentation.

BACKGROUND: The clinical efficacy of specific allergy vaccination (SAV), previously called specific immunotherapy is well documented. The working mechanism of this treatment is not completely known at present. Allergen-specific CD4+ T lymphocytes are activated at extremely low allergen concentrations in vivo possibly as a result of serum IgE-facilitated allergen presentation (S-FAP). Previously, we have shown that this process can be inhibited by long-term birch SAV sera. METHODS: In the present study, we have analysed sera from birch-allergic patients in a randomized double-blind, placebo-controlled clinical trial for their ability to mediate S-FAP. Birch-specific IgE levels were not changed after SAV. Bet v 1-specific IgE levels, however, were significantly decreased (P<0.05) and Bet v 1-specific IgG4 levels were strongly increased after SAV (P<0.001). None of these changes were observed in the placebo group. When the sera were tested for their ability to induce S-FAP, a complete abrogation of this effect was noted in the sera from patients receiving active treatment (P<0.001), but not in the control group. This inhibition of S-FAP seemed to be associated with the reduction in the ratio between Bet v 1-specific IgE and IgG4 antibodies in serum, but a clear correlation could not be demonstrated. CONCLUSION: In conclusion, the present study clearly shows that SAV leads to an inhibition of the S-FAP needed to obtain optimal T cell activation at the low allergen concentrations present in vivo. This novel mechanism may explain the increased allergen threshold levels found in allergen provocation tests and the reduction of late-phase reactions observed after SAV.