R.J.J. van Neerven

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

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.

Crossreactivity and T‐cell epitope specificity of Bet v 1‐specific T cells suggest the involvement of multiple isoallergens in sensitization to birch pollen

Background Allergen‐specific T lymphocytes play an important role in the pathophysiology of atopic disease. Detailed studies of their epitope‐specificity and crossreactivity are required for the development of novel approaches for specific immunotherapy.

Humanized Anti-IgE mAb Hu-901 Prevents the Activation of Allergen-Specific T Cells

Background: As a result of the very efficient capture of allergens by IgE that focuses to CD23 on B cells or FcΕRI on dendritic cells, allergen-specific T cells can be activated after exposure to very low levels of allergens. This IgE-mediated allergen presentation is 100- to 1,000-fold more efficient than fluid phase endocytosis. The aim of the present study was to determine whether humanized anti-IgE mAb Hu-901 can prevent the activation of allergen-specific T cells by inhibiting IgE-mediated allergen presentation. Methods: A house dust mite major allergen Der p 1-specific T cell line was generated from an allergic asthma patient, and a model was set up to show IgE-facilitated allergen presentation via CD23 on EBV-transformed B cells. In addition, experiments were performed by FACS analysis, detecting the presence of IgE-allergen complexes bound to EBV-B cells by polyclonal FITC-labeled anti-IgE antisera. Results: The anti-IgE mAb Hu-901 inhibited proliferation of allergen-specific T cells at low allergen concentrations. Inhibition was dose-dependent. This effect could be explained by Hu-901 inhibition of binding of allergen-IgE complexes to CD23 expressed on EBV-transformed B lymphocytes. Conclusions: These data clearly indicate that anti-IgE antibodies for the treatment of allergy exert their effect not only by inhibiting mast cell/basophil degranulation, but also by preventing T cell activation, which possibly explains the effect of anti-IgE treatment on late-phase reactions noted in clinical studies.

The Mucosal Factors Retinoic Acid and TGF-β1 Induce Phenotypically and Functionally Distinct Dendritic Cell Types

Non-inflammatory dendritic cell (DC) subsets play an essential role in preventing massive inflammation in mucosal tissues. We investigated whether mucosa-related factors, namely retinoic acid (RA) and transforming growth factor-β (TGF-β1), can induce such DC types. DCs were differentiated from monocytes in the absence or presence TGF-β1 and RA. The phenotype as well as responsiveness to bacterial ligands was studied in detail. Compared to monocyte-derived DCs (moDCs), the expression of co-stimulatory molecule CD86 and DC maturation marker CD83 were strongly reduced by RA and TGF-β1. In addition, both RA- and TGF-β1-induced DCs showed strongly decreased responsiveness to stimulation with the bacterial ligands lipopolysaccharide and peptidoglycan, and produced significantly lower levels of the pro-inflammatory cytokines IL-12 and TNF-α compared to moDCs, whilst IL-10 production was not significantly reduced. DCs differentiated under the influence of RA uniquely expressed markers related to intestinal homing (CD103 and integrin β7). In addition, CCR7, which mediates homing to lymph nodes, was expressed by DCs differentiated in the presence of RA, and also to a lesser extent by the other DC types. Furthermore, whereas moDCs and TGF-β1-derived moDCs expressed high levels of CD32, RA-derived DCs lacked CD32 expression but expressed high levels of CD64, suggesting that RA-DCs may primarily respond to soluble proteins and moDCs, and TGF-β DCs to immune complexes. The data presented here support the hypothesis that the mucosal factors TGF-β1 and RA, which can also be provided through dietary intake of dairy products, result in functionally and phenotypically distinct DC types with non-inflammatory properties.

Identification of isoform-specific T-cell epitopes in the major timothy grass pollen allergen, Phl p 5

The involvement of CD4+ T cells in the pathophysiology of atopic disease is well established.

Differential recognition of recombinant Phl p 5 isoallergens by Phl p 5-specific T cells.

Background: At present, recombinant allergens are considered for the diagnosis and treatment of atopic allergies. To evaluate the theoretical impact of isoallergen variation on the selection of isoallergens for specific allergy vaccination, we characterized the T–cell response of allergic patients to the Phleum pratense major allergen, Phl p 5, and five of its recombinant isoallergens. Methods: Phl p 5–specific T cell lines (TCLs) were isolated from the peripheral blood of 3 allergic rhinitis patients, and their reactivity patterns were studied in detail. Results: The TCLs were highly crossreactive with related grasses. The crossreactivity with Poa pratensis was more extensive than with Lolium perenne, directly reflecting the sequence identity between Phl p 5, Poa p 5, and Lol p 5. The TCLs produced IFN–γ and IL–4 simultaneously, resembling a Th0–like cytokine production profile. Interestingly, when T cell clones were tested with natural Phl p 5 and five rPhl p 5 isoallergens, a differential recognition pattern was found. One of the TCLs exclusively reacted with Phl p 5b, another reacted with all isoforms tested, and the third reacted strongly with native purified Phl p 5, but only weakly with all five recombinant isoallergens. Conclusion: These results indicate that Phl p 5–specific T cells are highly heterogeneous, and that they differentially recognize isoallergens. This indicates that when recombinant Phl p 5 is considered for allergy vaccination, a mixture of isoallergens representing the different isoallergen groups may clinically prove to be more effective than single isoallergens.

Immunological Mechanisms of Anti-lgE Treatment

Non-anaphylactogenic anti-IgE mAb have been developed over the past decade to treat atopic allergies. These antibodies neutralize circulating IgE molecules, and thus prevent IgE from binding to its receptors, FCERI and CD23. Efficacy of anti-IgE treatment has been shown in several clinical trials,and new, unanticipated, mechanisms by which anti-IgE exerts its clinical effect are being discovered. Here we summarize a number of studies on the immunological mechanisms underlying anti-IgE treatment.