Amanda J. Reefer

A role for IL-10-mediated HLA-DR7-restricted T cell-dependent events in development of the modified Th2 response to cat allergen.

Although high dose exposure to inhaled cat allergen (Fel d 1) can cause a form of tolerance (modified Th2 response), the T cell mechanism for this phenomenon has not been studied. T cell responses to Fel d 1 were characterized in both allergic (IgEpos) and modified Th2 (IgEnegIgGpos) responders as well as serum Ab-negative controls (IgEnegIgGneg). Fel d 1 stimulated high levels of IL-10 in PBMC cultures from all individuals, with evidence of Th2 and Th1 cytokine skewing in allergic and control subjects, respectively. Using overlapping peptides, epitopes at the N terminus of Fel d 1 chain 2 were shown to stimulate strong T cell proliferation and to preferentially induce IL-10 (peptide 2:1 (P2:1)) or IFN-γ (P2:2) regardless of the allergic status of the donor. Injection of cat extract during conventional immunotherapy stimulated expansion of IL-10- and IFN-γ-producing chain 2 epitope-specific T cells along with increased Fel d 1-specific serum IgG and IgG4 Ab. Six of 12 modified responders expressed the major HLA-DRB1 allele, *0701, and both P2:1 and P2:2 were predicted ligands for this allele. Cultures from DR7-positive modified responders produced the highest levels of IL-10 to P2:1 in addition to other major and minor epitopes within chains 1 and 2. In the presence of anti-IL-10 mAb, both T cell proliferation and IFN-γ production were enhanced in a Fel d 1- and epitope-specific manner. We conclude that IL-10-producing T cells specific for chain 2 epitopes are relevant to tolerance induction, and that DR7-restricted recognition of these epitopes favors a modified Th2 response.

Analysis of CD25hiCD4+ “regulatory” T-cell subtypes in atopic dermatitis reveals a novel TH2-like population

BACKGROUND It is unresolved whether circulating CD25hiCD4+ T cells in patients with atopic dermatitis who have elevated IgE (IgE(high)) are regulatory or effector in nature. OBJECTIVE To analyze the properties of CD25hi T-cell subtypes in IgE(high) atopic dermatitis. METHODS The phenotype of circulating CD25hi T cells was analyzed by flow cytometry using PBMCs from patients with atopic dermatitis (total IgE > 250 IU/mL). Cytokines induced in CD25hi subtypes were analyzed after activation with anti-CD3 mAb (+/-IL-2) and in the presence of activated autologous effector T cells (CD25negCD4+). Reactivity to bacterial superantigen derived from the skin-colonizing organism Staphylococcus aureus was also evaluated. RESULTS CD25(hi) T cells expressing regulatory T-cell markers (Foxp3, CCR4, cutaneous lymphocyte-associated antigen) were increased in atopic dermatitis compared with IgE(low) controls. This phenomenon was linked to disease severity. Two subtypes of CD25hi T cells were identified on the basis of differential expression of the chemokine receptor CCR6. Although the ratio of CCR6+ and CCR6neg subtypes within the CD25hi subset was unaltered in atopic dermatitis, each subtype proliferated spontaneously ex vivo, suggesting in vivo activation. Activated CCR6neg cells secreted T(H)2 cytokines, and coculture with effector T cells selectively enhanced IL-5 production. Moreover, induction of a T(H)2-dominated cytokine profile on activation with bacterial superantigen was restricted to the CCR6neg subtype. CONCLUSION Despite a regulatory phenotype, activated CD25hi T cells that lack expression of CCR6 promote T(H)2 responses.

Targeting allergen to FcγRI reveals a novel TH2 regulatory pathway linked to thymic stromal lymphopoietin receptor

BACKGROUND The molecule H22-Fel d 1, which targets cat allergen to FcgammaRI on dendritic cells (DCs), has the potential to treat cat allergy because of its T-cell modulatory properties. OBJECTIVE We sought to investigate whether the T-cell response induced by H22-Fel d 1 is altered in the presence of the T(H)2-promoting cytokine thymic stromal lymphopoietin (TSLP). METHODS Studies were performed in subjects with cat allergy with and without atopic dermatitis. Monocyte-derived DCs were primed with H22-Fel d 1 in the presence or absence of TSLP, and the resulting T-cell cytokine repertoire was analyzed by flow cytometry. The capacity for H22-Fel d 1 to modulate TSLP receptor expression on DCs was examined by flow cytometry in the presence or absence of inhibitors of Fc receptor signaling molecules. RESULTS Surprisingly, TSLP alone was a weak inducer of T(H)2 responses irrespective of atopic status; however, DCs coprimed with TSLP and H22-Fel d 1 selectively and synergistically amplified T(H)2 responses in highly atopic subjects. This effect was OX40 ligand independent, pointing to an unconventional TSLP-mediated pathway. Expression of TSLP receptor was upregulated on atopic DCs primed with H22-Fel d 1 through a pathway regulated by FcgammaRI-associated signaling components, including src-related tyrosine kinases and Syk, as well as the downstream molecule phosphoinositide 3-kinase. Inhibition of TSLP receptor upregulation triggered by H22-Fel d 1 blocked TSLP-mediated T(H)2 responses. CONCLUSION Discovery of a novel T(H)2 regulatory pathway linking FcgammaRI signaling to TSLP receptor upregulation and consequent TSLP-mediated effects questions the validity of receptor-targeted allergen vaccines.

Mechanisms of allergy and clinical immunologyTargeting allergen to FcγRI reveals a novel TH2 regulatory pathway linked to thymic stromal lymphopoietin receptor

BACKGROUND The molecule H22-Fel d 1, which targets cat allergen to FcgammaRI on dendritic cells (DCs), has the potential to treat cat allergy because of its T-cell modulatory properties. OBJECTIVE We sought to investigate whether the T-cell response induced by H22-Fel d 1 is altered in the presence of the T(H)2-promoting cytokine thymic stromal lymphopoietin (TSLP). METHODS Studies were performed in subjects with cat allergy with and without atopic dermatitis. Monocyte-derived DCs were primed with H22-Fel d 1 in the presence or absence of TSLP, and the resulting T-cell cytokine repertoire was analyzed by flow cytometry. The capacity for H22-Fel d 1 to modulate TSLP receptor expression on DCs was examined by flow cytometry in the presence or absence of inhibitors of Fc receptor signaling molecules. RESULTS Surprisingly, TSLP alone was a weak inducer of T(H)2 responses irrespective of atopic status; however, DCs coprimed with TSLP and H22-Fel d 1 selectively and synergistically amplified T(H)2 responses in highly atopic subjects. This effect was OX40 ligand independent, pointing to an unconventional TSLP-mediated pathway. Expression of TSLP receptor was upregulated on atopic DCs primed with H22-Fel d 1 through a pathway regulated by FcgammaRI-associated signaling components, including src-related tyrosine kinases and Syk, as well as the downstream molecule phosphoinositide 3-kinase. Inhibition of TSLP receptor upregulation triggered by H22-Fel d 1 blocked TSLP-mediated T(H)2 responses. CONCLUSION Discovery of a novel T(H)2 regulatory pathway linking FcgammaRI signaling to TSLP receptor upregulation and consequent TSLP-mediated effects questions the validity of receptor-targeted allergen vaccines.