Normal human immunoglobulin G4 is bispecific: it has two different antigen-combining sites.
(9/409)
Unlike other immunoglobulin G (IgG) subclasses, IgG4 antibodies in plasma have been reported to be functionally monovalent. In this paper we show that the apparent monovalency of circulating IgG4 is caused by asymmetry of plasma IgG4. A large fraction of plasma IgG4 molecules have two different antigen-binding sites, resulting in bispecificity. Sera from patients with IgG4 antibodies to both house dust mite and grass pollen induced cross-linking of Sepharose-bound grass pollen antigen to radiolabelled house dust mite allergen Der p I. This bispecific binding activity was not observed in sera with IgG4 antibodies to either grass pollen or house dust mite exclusively. Depletion of IgG4 antibodies resulted in disappearance of the bispecific activity. By size exclusion chromatography we excluded the possibility that bispecific activity was caused by aggregation of IgG4 antibodies. These results indicate that circulating (polyclonal) IgG4 antibodies have two different antigen-binding sites and therefore are functionally monovalent antibodies. (+info)
TCR-mediated activation of allergen-specific CD45RO(+) memory T lymphocytes results in down-regulation of cell-surface CXCR4 expression and a strongly reduced capacity to migrate in response to stromal cell-derived factor-1.
(10/409)
The selective migration of functional T(h) lymphocyte subsets with different cytokine production profiles into inflamed tissue is likely to depend on the state of activation of the cells, as well as on the differential expression of various adhesion molecules and chemokine receptors. In this study, we have analyzed the effect of allergen-specific activation on the expression of the chemokine receptor CXCR4 on T lymphocytes. We show that stimulation of peripheral blood mononuclear cells from atopic patients with the allergen Der p results in down-regulation of CXCR4 surface expression on Der p-activated CD25(+)CD45RO(+) antigen-specific memory cells which was caused by a decrease in CXCR4 gene transcription and did not seem to be mediated by endogenous cytokines, such as IFN-gamma. In contrast, however, CXCR4 surface expression was enhanced on naive CD25(-)CD45RO(-) and resting CD25(-)CD45RO(+) memory T cells, as a result of the presence of endogenous IL-4, most likely produced by Der p-activated memory T cells. Antigen-specific CD25(+)CD45RO(+) T lymphocytes, purified 7 days after stimulation with Der p, had a strongly reduced capacity to migrate in response to stimulation with stromal cell-derived factor (SDF)-1, the ligand for CXCR4. Together, these results suggest that differential expression of CXCR4 on activated and resting T cells is due to the counteracting effects of TCR-mediated down-regulation and IL-4-mediated up-regulation of this chemokine receptor respectively, and furthermore indicate that antigen-activated memory T cells are unlikely to migrate into inflamed tissue in response to SDF-1. (+info)
Monoclonal antibodies to recombinant Der p 2, a major house dust mite allergen: specificity, epitope analysis and development of two-site capture ELISA.
(11/409)
House dust mite allergens have been well established as sensitizing agents that are important in the induction of allergic diseases. In order to analyze epitopes of the allergen and to develop a quantitative method of the allergen exposure, monoclonal antibodies against a recombinant Der p 2 (rDer p 2), one of the major allergens of Dermatophagoides pteronyssinus, were produced. Four monoclonal antibodies produced were species-specific and did not cross-react to the D. farinae crude extract. Two of the monoclonal antibodies were found to be IgG1 and the others were IgM. For the analysis of epitopes, a Der p 2 cDNA encoding 126 amino acids (aa) was dissected into three fragments with several overlapping peptides. A (aa residues 1-49), B (44-93), and C fragment (84-126). Three monoclonal antibodies showed reactivities to the recombinant B fragment and to the full-length rDer p 2, but one monoclonal antibody reacted only with the full-length rDer p 2. Two-site capture ELISA was developed using two different monoclonal antibodies for quantitating Der p 2 in house dust. The sensitivity limit was 4 ng/ml with rDer p 2 and 8 micrograms/ml with the D. pteronyssinus crude extract. The result suggested that the assay using monoclonal antibodies against rDer p 2 could be useful for the environmental studies and for the standardization of mite allergen extracts. (+info)
Phosphorothioate oligodeoxynucleotides promote the in vitro development of human allergen-specific CD4+ T cells into Th1 effectors.
(12/409)
DNA vaccination is an effective approach in inducing the switch of murine immune responses from a Th2 to a Th1 profile of cytokine production that has been related to the activity of unmethylated CpG motifs present in bacterial, but not mammalian, DNA. We report here that some synthetic phosphorothioate, but not phosphodiester, oligodeoxynucleotides (ODNs) were able to induce B cell proliferation and to shift the in vitro differentiation of Dermatophagoides pteronyssinus group 1-specific human CD4+ T cells from atopic donors into Th cell effectors showing a prevalent Th1, instead of Th2, cytokine profile. This latter effect was completely blocked by the neutralization of IL-12 and IFN (alpha and gamma) in bulk culture, suggesting that the Th1-inducing activity of phosphorothioate ODNs was mediated by their ability to stimulate the production of these cytokines by monocytes, dendritic, and NK cells. Cytosine methylation abolished the Th1-inducing activity of ODNs; however, CpG dinucleotide-containing ODNs exhibited the Th1-shifting effect independently of the presence or the absence of CpG motifs (5'-pur-pur-CpG-pyr-pyr-3'). Moreover, the inversion of CpG to GpC resulted only in a partial reduction of this activity, suggesting that the motif responsible for the Th1-skewing effect in humans is at least partially different from that previously defined in mice. These results support the concept that the injection of allergens mixed to, or conjugated with, appropriate ODNs may provide a novel allergen-specific immunotherapeutic regimen for the treatment of allergic disorders. (+info)
Low dose of orally administered antigen down-regulates the T helper type 2-response in a murine model of dust mite hypersensitivity.
(13/409)
One of the main goals of immunotherapy of allergic diseases is the down-regulation of the type I hypersensitivity reaction. We investigated in this study the effect of oral administration of varying doses (0.25, 1.0, 4.0 and 10 mg) of dust mite extract (Dermatophagoides pteronyssinus, Dp) in sensitized A/Sn mice. A marked decrease of the allergen-specific immunoglobulin E (IgE) response was observed with all antigen doses. The mice orally tolerized with low Dp dose (0.25 mg) had a significant decrease in the total serum IgE and in the immunoglobulin G1 (IgG1), IgG2a and IgG2b antibody levels. The higher Dp dose (10.0 mg), however, enhanced the IgG1 antibody response, suggesting the stimulation of a pre-existing immune response of the sensitized animals. Animals fed with the low Dp dose had a significant decrease in the frequency of interleukin-4 (IL-4) secreting cells. These animals also showed a significant decrease in the frequency of Dp-specific IgE- and IgG1-positive plasma cells. Our data suggest that feeding dust mite extract to Dp-sensitized mice down-regulates the development of type I hypersensitivity, by inhibition of the T helper 2 response. (+info)
CD4(+) T cells induced by virus-like particles expressing a major T cell epitope down-regulate IL-5 production in an ongoing immune response to Der p 1 independently of IFN-gamma production.
(14/409)
It has been previously demonstrated that hybrid Ty virus-like particles (VLP) prime effective CD8(+) and CD4(+) T cell responses. In this study, we investigated the effect of treating mice with Ty VLP carrying the immunodominant epitope of Der p 1 after sensitizing them to the group 1 allergen of the house dust mite Dermatophagoides pteronyssinus (Der p 1), under conditions that induce T(h)2 immunity. We show that i.p. treatment with the hybrid VLP abrogated allergen-specific IL-5 production and reduced allergen-specific cell proliferation. This suppression of the response was mediated by CD4(+) T cells and was not accompanied by an increase in IFN-gamma production. (+info)
The cysteine protease activity of the major dust mite allergen Der p 1 selectively enhances the immunoglobulin E antibody response.
(15/409)
The house dust mite Dermatophagoides pteronyssinus allergen Der p 1 is the most immunodominant allergen involved in the expression of dust mite-specific immunoglobulin (Ig)E-mediated hypersensitivity. The reason for this potent IgE-eliciting property of Der p 1 remains unknown, but there is mounting in vitro evidence linking the allergenicity of Der p 1 to its cysteine protease activity. Here we demonstrate for the first time that immunization of mice with proteolytically active Der p 1 results in a significant enhancement in total IgE and Der p 1-specific IgE synthesis compared with animals immunized with Der p 1 that was irreversibly blocked with the cysteine protease inhibitor E-64. We conclude that the proteolytic activity of Der p 1 is a major contributor to its allergenicity. (+info)
Role of B7-CD28/CTLA-4 costimulation and NF-kappa B in allergen-induced T cell chemotaxis by IL-16 and RANTES.
(16/409)
The mechanisms that cause T cell recruitment into inflamed airways of asthmatic individuals are poorly understood. It has been shown previously that both natural exposure to allergen and challenge in the laboratory induce T cell accumulation in the bronchial mucosa of sensitized asthmatics. To study the mechanisms involved in this process, we have used an explant model in which bronchial biopsies taken from mild atopic asthmatic volunteers during fiberoptic bronchoscopy were stimulated in culture for 24 h by the common aeroallergen house dust mite (Dermatophagoides pteronyssinus (Der p)). Analysis of culture supernatants showed that stimulation with Der p significantly enhanced both the generation of T cell chemotactic activity by the mucosal tissue, as assayed in microchemotaxis chambers, and the production of IL-16 and RANTES. Neutralization experiments showed that IL-16 contributed more to the chemotactic activity than RANTES. The fusion protein CTLA-4-Ig, blocking B7:CD28 costimulation, and dexamethasone both significantly reduced the ex vivo production of chemotactic activity and release of IL-16 and RANTES. The proteasome inhibitor Cbz-Ile-Glu(OtBu)-Ala-leucinal also had a significant inhibitory effect on T cell chemotactic activity and IL-16 but not RANTES generation, indicating a role for nuclear factor NF kappa B activation. These results indicate that allergen stimulates cells within the bronchial mucosa to increase IL-16 and RANTES release, both of which contribute to T cell accumulation in asthmatic airways. The allergen-induced chemotactic activity is dependent on cell activation via CD28 and involves, at least partly, NF-kappa B. (+info)