Time course of serum inhibitory activity for facilitated allergen-IgE binding during bee venom immunotherapy in children.

BACKGROUND: Immunotherapy for bee venom allergy is effective and provides long-term protection. Venom-specific IgG4 levels are increased but with no correlation with clinical improvement. Following grass pollen immunotherapy, elevation of antigen-specific IgG4 is accompanied by increases in IgG-dependent serum inhibitory activity for IgE-facilitated binding of allergen-IgE complexes to B cells. As this 'functional' assay of inhibitory antibodies may be more predictive of clinical efficacy, we investigated the time course of serum inhibitory activity for IgE-facilitated antigen binding during venom immunotherapy (VIT) in children and following 2 years of VIT withdrawal. METHODS: Ten bee venom-allergic children (mean age: 9.3 years; m/f, 7/3) with moderate to severe allergic reactions to bee stings received VIT. A separate group of seven children (mean age: 14 years; m/f, 5/2) were investigated 2 years after VIT withdrawal. Ten age- and gender-matched children served as non-allergic controls. Allergen-specific serum IgG4 and IgE levels were measured by ELISA at baseline, after 2 years of VIT and 2 years after VIT withdrawal. Serum inhibitory activity was assessed using the facilitated-allergen binding (FAB) assay. RESULTS: Sera obtained during VIT significantly inhibited allergen-IgE binding to B-cells (pre-treatment=104+/-23%; 2 years=46+/-15%; P<0.001) when compared with sera obtained after treatment withdrawal and sera from normal controls. In parallel to FAB inhibition during VIT, significantly higher IgG4 levels were noted after immunotherapy (pre-treatment=8.6+/-2.3 AU; 2 years=26.7+/-3.5 AU; P<0.001) compared with those observed after withdrawal and in the controls. In contrast, progressively lower IgE concentrations were observed compared with pre-treatment (44+/-7 AU) in sera obtained after 2 years of VIT (25+/-5 AU; P<0.01) and 2 years following the withdrawal of VIT (10+/-3 AU; P<0.05). CONCLUSIONS: In contrast to grass pollen immunotherapy, the persistent decline in venom-specific IgE levels, rather than serum inhibitory activity for FAB, may be more relevant for long-term clinical efficacy of VIT.

Distinct regulation of IgE, IgG4 and IgA by T regulatory cells and toll-like receptors.

BACKGROUND: Allergic diseases are characterized by the activation of the immune system and formation of immunoglobulin (Ig)E antibodies against normally innocuous environmental antigens, whereas IgG4 and IgA represent noninflammatory and blocking antibody isotypes. The T helper 2 (Th2) cells induce and T regulatory (Treg) cells suppress several features of allergic inflammation. Our aim was to investigate the role of allergen-specific T regulatory type 1 (Tr1) cells and CD4(+)CD25(+) Treg cells and toll-like receptors (TLRs) on IgE, IgG4 and IgA production. METHODS: Germline or productive Ig-transcripts are determined by real-time reverse transcriptase-polymerase chain reaction, secreted Igs are measured by enzyme-linked immunosorbent assay and the frequency of Ig-producing plasma cells is investigated by enzyme-linked immunosorbent spot. Circulating CD4(+)CD25(+) Treg cells and allergen-specific Tr1 cells are used. RESULTS: Both allergen-specific, interleukin-10-secreting Tr1 cells and CD4(+)CD25(+) Treg cells from healthy individuals induced IgG4 and suppressed IgE production in peripheral blood mononuclear cells and purified B-cell cultures. In contrast, induction of IgA production is independent of T-cell help and the role of Tr1 or Treg cells is very limited, whereas it was highly induced by direct B-cell activation via TLR7 and 9. CONCLUSIONS: These data suggest that T regulatory cells may contribute to the suppression of allergic diseases by suppression of IgE and induction of IgG4, whereas IgA production is enhanced by B-cell activation via TLR7 and TLR9.

Induction of interleukin-10 and suppressor of cytokine signalling-3 gene expression following peptide immunotherapy.

BACKGROUND: Allergen-derived (T cell epitope) peptides may be safer for immunotherapy than native allergen, as they do not cross-link immunoglobulin (Ig)E. However, HLA polymorphism results in multiple potential epitopes. Synthetic peptides of phospholipase (PL) A(2) were selected for a peptide vaccine, on the basis of binding affinity for commonly expressed HLA-DR molecules. OBJECTIVE: To evaluate treatment with an HLA-DR-based PLA(2) peptide vaccine in subjects with mild honeybee allergy in an open, controlled study. METHODS: Twelve volunteers with allergy to bee venom received nine intradermal injections of PLA(2) peptides, with six untreated subjects serving as controls. Outcome was assessed by the size of the late-phase cutaneous reaction to allergen, peripheral blood mononuclear cell (PBMC) proliferation, cytokine release, and expression of genes associated with immune regulation. RESULTS: Subjects receiving peptides showed a decrease in the magnitude of the late-phase cutaneous reaction to bee venom compared with controls (P=0.03). The proliferation of venom-stimulated PBMCs decreased in treated subjects compared with controls (P=0.01). Peptide treatment reduced the production of IL-13 by PLA(2)-stimulated PBMCs (P<0.01) and IFN-gamma (P<0.01), and increased the production of IL-10 (P=0.02). Transcription of the suppressor of cytokine signalling (Socs)3 gene was significantly increased following therapy. A transient, but modest, increase in allergen-specific IgG was also observed. CONCLUSION: HLA-DR-based T cell epitopes modify surrogate markers associated with successful immunotherapy and induction of immune regulation, supporting the concept that this form of treatment may be efficacious in human allergic disease.

Histamine regulates T-cell and antibody responses by differential expression of H1 and H2 receptors.

Many pathological processes, including those causing allergies and autoimmune diseases, are associated with the presence of specialized subsets of T helper cells (TH1 and TH2) at the site of inflammation. The diversity of TH1 and TH2 function is not predetermined but depends on signals that drive the cells towards either subset. Histamine, released from effector cells (mast cells and basophils) during inflammatory reactions can influence immune response. Here we report that histamine enhances TH1-type responses by triggering the histamine receptor type 1 (H1R), whereas both TH1- and TH2-type responses are negatively regulated by H2R through the activation of different biochemical intracellular signals. In mice, deletion of H1R results in suppression of interferon (IFN)-gamma and dominant secretion of TH2 cytokines (interleukin (IL)-4 and IL-13). Mutant mice lacking H2R showed upregulation of both TH1 and TH2 cytokines. Relevant to T-cell cytokine profiles, mice lacking H1R displayed increased specific antibody response with increased immunoglobulin-epsilon (IgE) and IgG1, IgG2b and IgG3 compared with mice lacking H2R. These findings account for an important regulatory mechanism in the control of inflammatory functions through effector-cell-derived histamine.

Cytokine network and dysregulated apoptosis in atopic dermatitis.

Activation and skin-selective homing of peripheral blood memory/effector T cells and effector functions in the skin represent sequential immunological events in the pathogenesis of atopic dermatitis (AD). T cells infiltrating the skin utilize the cutaneous lymphocyte-associated antigen (CLA) and other receptors to recognize and cross the vascular endothelium. In the peripheral blood of AD patients, both CD4+ and CD8 subsets of CLA+CD45RO+ T cells are in an activated state with high CD25, HLA-DR, and CD40-ligand expression. They express upregulated Fas and Fas-ligand and undergo activation-induced apoptosis. After homing to skin these T cells form dermal infiltrates which play a key role in the pathogenesis of the disease. Skin-infiltrating T cells in AD are protected from activation-induced cell death, although they express both Fas and Fas-ligand. They are protected from apoptosis by cytokines such as IL-2, IL-4, and IL-15 and extracellular matrix components such as fibronectin and transferrin. CLA+, skin-homing T cells may play a role in peripheral blood eosinophilia and hyper IgE production by high IL-5 and IL-13 expression, respectively. These T cells secrete IFN-gamma in the skin, which upregulates Fas on keratinocytes and renders them susceptible to apoptosis. Keratinocyte apoptosis is induced by Fas-ligand, either soluble or expressed on the surface of T cells, leading to eczema formation. Here we discuss the mechanisms of skin-selective T cell homing and activation, and emphasize the concept of dysregulated apoptosis of T cells, eosinophils, and keratinocytes as essential pathogenetic episodes in AD and other eczematous disorders.

Histamine upregulates Th1 and downregulates Th2 responses due to different patterns of surface histamine 1 and 2 receptor expression.

Histamine, which acts via G protein-coupled receptors, is an important mediator of immediate hypersensitivity and is also able to influence the nature of T cell responses. We demonstrated that TH1 and Th2 cells express distinct surface histamine receptor patterns and that Th1-type responses are enhanced by histamine, whereas Th2-type responses are negatively regulated, due to different intracellular signals generated by histamine stimulation. These findings account for negative feedback regulation in a wide variety of pathologies.

Expression of cutaneous lymphocyte-associated antigen on human CD4(+) and CD8(+) Th2 cells.

The cutaneous lymphocyte-associated antigen (CLA) represents the homing receptor involved in selective migration of memory/effector T cells to the skin. Numerous reports demonstrated distinct CLA expression on Th1 cells. However, T cells isolated from skin lesions and CLA(+) T cells circulating in peripheral blood of atopic dermatitis patients expressed high IL-5 and IL-13. Accordingly, we investigated the regulation of CLA on human type 1 and type 2 T cells. CLA was induced on freshly generated Th1 and Tc1 cells only, but not on those of type 2. Anti-CD3 stimulation was sufficient to induce CLA on Th2 cells in the absence of serum in the culture medium. In serum containing medium, IL-4 inhibited CLA and related alpha-fucosyltransferase mRNA expression. IL-12 and/or staphylococcal enterotoxin B (SEB) stimulation up-regulated CLA expression on either Th2 and Tc2 cells. On stimulation with IL-12, CLA was expressed on the surface of bee venom phospholipase A(2)-specific Th1, Th2, Th0 and T regulatory 1 clones, representing non-skin-related antigen-specific T cells. In addition, CLA could be re-induced on T cells that had lost CLA expression upon resting. These results suggest that skin-selective homing is not restricted to functional and phenotypic T cell subsets.