Human T cell clones can induce in vitro IgE synthesis in normal B cells regardless of alloantigen recognition or specificity for peculiar antigens

Human T-Cell Cloning by Limiting Dilution

Human T cells represent a heterogeneous population, including cells with different phenotypical and function properties. Despite, in the last years, several technologies were developed to investigate phenotypical properties of T cells at single cell level, in vitro T cell clone 's culture remains the only way to perform functional study on T cells at single cell levels. Here, we describe the method to obtain human T cell clones by limiting dilution in the presence of feeder cells and to maintain them in culture for further investigations.

Cytokines Involved in the Pathophysiology of IgE Response

Recent data in both mouse and human systems have clearly indicated that IL-4 plays an essential role in the induction of IgE response, whereas IFN-γ exerts an opposite effect on this phenomenon. However, IL-4 alone is unable to induce IgE synthesis. A prior membrane contact signal delivered by activated T cells is required by B cells to synthesize IgE in response to IL-4. A cognate interaction between B and T cells producing IL-4 (but not IFN-γ) is optimal for induction of IgE synthesis. However, when such IL-4 producing T cells are activated, they may provide B cells with a membrane signal, through a non-cognate interaction, which also results in induction of IgE synthesis. Other cytokines, such as IL-2 and IL-6, play an auxiliary role in IL-4 dependent IgE production.

Analyses at the clonal level of the profile of cytokine production by helper T cells have shown that imbalances between IL-4 and IFN-γ producing T cells can be detected in patients with hyperproduction of IgE. In children with hyper-IgE syndrome a strong reduction of circulating T cells able to produce IFN-γ (and TNF-α) was found, whereas both, reduction of IFN-γ-producing and increase of IL-4 producing T cells were found in patients with parasitic infestation. In allergic inflammatory infiltrates, such as those found in vernal conjuctivitis, helper T cells able to produce IL-4 and to induce IgE synthesis accounted for the large majority of infiltrating T cells. It is reasonable to suggest that systemic or microenvironmental alterations of the balance between IL-4- and IFN-γ-producing T cells may be involved, at least in part, in the pathophysiology of the increased igE response occurring in a number of human diseases.

Determinants of bronchial responsiveness in the European Community Respiratory Health Survey in Italy: evidence of an independent role of atopy, total serum IgE levels, and asthma symptoms

The aim of the analysis was to test whether total serum IgE levels, specific serum IgE levels, and asthma symptoms are independent predictors of bronchial hyperresponsiveness (BHR), after controlling for known risk factors or potential confounders. The study was carried out on a sample of 875 young adults, 20-44 years old, who took part in the European Community Respiratory Health Survey in Italy. The subjects underwent a dose-response methacholine challenge test. We also measured airway caliber as the baseline FEV1 in absolute terms and as percentage of forced vital capacity (FVC); skin wheal response to 11 common environmental allergens; and total and specific serum IgE levels to mites, molds, pets, and respiratory symptoms by means of a standardized questionnaire. Atopy (positive skin prick test and/or positive specific IgE assay), total IgE, asthma symptoms, airway caliber, and age appeared to be independent predictors of BHR. When all the other risk factors were taken into account, atopy and total IgE were associated with a threefold increase in BHR risk and thus emerged as the main determinants of BHR. The importance of symptom status as a determinant of BHR decreased remarkably after controlling for atopy and IgE: the odds ratio of current asthmatics to asymptomatic subjects decreased from 15.3 to 8.8. When controlling for symptoms and atopy, a family history of allergic diseases and early respiratory infections was not found to be associated with BHR. Both FEV1 and FEV1/FVC were strongly and inversely associated with BHR. When airway caliber was taken into account, older age was associated with decreased responsiveness, and the level of responsiveness did not differ significantly between males and females and between smokers and nonsmokers. The results from this analysis indicate that at any given age, irrespective of sex and smoking habits, total serum IgE, specific IgE, airway caliber, and asthma symptoms are the main independent factors influencing the occurrence of BHR in a young adult sample.

Suppression of interleukin 4 production from type 2 helper T cell clone by antisense oligodeoxynucleotide

Type 2 helper T cell (Th2) clone has been reported to secrete interleukin (IL) 4 and IL5 in response to the specific antigen presented by syngeneic antigen-presenting cells. In the present report, we synthesized phosphorothioate analogue of an antisense oligodeoxynucleotide complementary to nucleotide 17-36 of IL4 mRNA (S-oligo), and tested its ability to inhibit IL4 production from a Th2 clone, D10.G4.1. (D10). D10 cells were cultured with mitomycin C-treated C3H spleen cells in the presence of 100 micrograms/ml conalbumin for 48-72 h. Secreted IL4 and IL5 were assayed biologically using HT2 cells and dextran sulfate-stimulated murine B cells, respectively. When 5-10 micrograms/ml S-oligo was added to the culture, IL4 production from D10 was suppressed by 70-90%. The same concentrations of S-oligo inhibited neither the antigen-induced proliferation of D10 nor the secretion of IL5 from the Th2 clone. These results suggest that this S-oligo is useful for inhibiting the production of IL4 preferentially without affecting other functions of Th2 cells.

Enhancement of antigen-induced interleukin 4 and IgE production by specific IgG1 in murine lymphocytes

Conalbumin (CA)-specific type 2 helper T cell (Th2) clone, D10G4.1 (D10) produces IL4 when stimulated with varying doses of TNP-CA in the presence of mitomycin C-treated C3H spleen cells or purified B cells as antigen-presenting cells (APC). The production of IL4 was assessed by bioassay and by expression of IL4 mRNA. IL4 production reached maximum at 100 micrograms/ml of TNP-CA, whereas 1 microgram/ml of the antigen induced less than 10% of the maximum level of IL4. This lower level of IL4 production was augmented to the maximum level when monoclonal anti-TNP IgG1 was added to the culture at 0.5-1 microgram/ml. Anti-TNP IgE, but not anti-TNP IgM, was also effective, though IgE was 1/10 as effective as IgG1. IgG1 with an irrelevant specificity and F(ab')2 of anti-TNP IgG1 did not show augmenting effects. Moreover, the enhancement by anti-TNP IgG1 was completely abolished by monoclonal antibody against murine Fc gamma RII, 2.4G2. These results suggest that a low dose of the antigen complexed with IgG1 is focused on APC by means of Fc gamma RII, processed, and presented efficiently to the Th2 clone. On the other hand, the co-culture of D10 with normal C3H B cells in the presence of 1-100 micrograms/ml TNP-CA resulted in polyclonal IgE production. Anti-TNP IgG1 markedly augmented the lower level of IgE production induced by a suboptimal dose of the antigen (1 microgram/ml). This augmentation was shown to be dependent on endogenous IL4 because the enhancement was abolished by monoclonal anti-IL4 (11B11).

Functional heterogeneity of human T cell clones from atopic and non-atopic donors

Several distinct T helper (TH) subsets have been identified, based on the cytokines secreted. Recently, it has been demonstrated that these subsets can regulate the isotype of humoral responses. To investigate the possible differences in TH subsets between atopic donors which have elevated serum IgE and donors with normal serum IgE, we examined series of human TH cell clones. A total of 31 and 22 CD4+ T cell clones from the atopic and non-atopic donors, respectively, were characterized for the ability to help for IgE synthesis in vitro. T cell clones generated with allergen AgE from the atopic donor were autoreactive and all induced IgE synthesis. Tetanus toxoid-specific (TT) and phytohaemagglutinin clones were generated from both donors. There was significant heterogeneity between the T cells isolated with different stimuli from the same atopic donor. Also, there was a significant difference in the number of T cells generated from the atopic versus the non-atopic donor which helped for IgE, although there was no significant difference between the total number of T cells able to help for immunoglobulin synthesis of other isotypes. Most importantly, there was a higher frequency of clones able to support IgE synthesis between TT-specific T cell clones generated from the atopic versus the non-atopic donor. These results suggest that there are changes in subsets of TH cells specific for microbial antigens as well as allergens in atopics, which may have important implications for the aetiology of atopic disease.

Regulation of IgE synthesis by cytokines

Considerable progress has been made in our understanding of the mechanisms underlying regulation of human IgE synthesis. Interleukin-4 induces IgE production specifically, but costimulatory signals provided by T cells are required. Other cytokines modulate interleukin-4-induced IgE synthesis. The roles of T cells and cytokines in regulating IgE switching are discussed.

What determines an antigen-specific IgE isotypic response? A hypothesis

Two models to account for an antigen-specific IgE isotypic response are proposed. Both models assume a first-tiered IgE production induced by antigen and IL-4; however, the processed IgE or Ag-IgE immune complexes stimulate T epsilon cells differently in the two models. In Model I, we propose that T epsilon cells express conventional T-cell receptors which recognize IgE isotypic determinants. Model IA proposes that IgE fragments are processed and recognized along with class II MHC molecules, and T epsilon cell preferentially act on antigen-activated IgE-committed B epsilon cells via recognition of processed membrane IgE determinants but not antigens; thus T epsilon cells are in principle capable of modulating non-antigen-specific polyclonal IgE responses. Model IB proposes that IgE function as a class-restriction determinant for nominal antigens analogous to that of class II molecules, and T epsilon cells exert stringent antigen-specific IgE isotypic responses by recognizing nominal antigens restricted to IgE. T epsilon cells thus exert antigen-specific and IgE concerted immunoregulation, and do not participate in modulating polyclonal IgE production. Model II proposes a heterotypic interaction of IgE with a cell interaction receptor (or IgE Fc receptor) on T cells. T epsilon cells modulate antigen-specific IgE isotypic responses via ligation with IgE-antigen immune complexes on B-cell surface; thus, T epsilon cells in principle contribute to polyclonal IgE responses.

Regulation and deregulation of human IgE synthesis

The IgE antibody system is among the most sophisticated of immune defense mechanisms. IgE molecules bind specifically and avidly to receptors localized on the surface of tissue mast cells and circulating basophils. These cells can produce and release several potent mediators after antigen interaction with a small number of surface-bound IgE molecules. The enormous amplification power of the IgE antibody system not only provides an important defense mechanism against parasites, but is also responsible for a number of clinical disorders. The human pathological condition most commonly associated with hyperproduction of IgE is atopy, the familial allergic disorder of immediate-type hypersensitivity to environmental allergens. In this paper Sergio Romagnani summarizes current understanding of the mechanisms involved in IgE regulation. Such studies are of primary importance in defining alterations responsible for the pathological conditions characterized by hyperproduction of IgE.

The immune complex: possible ways of regulating the antibody response

B cells express antigen, Fc and complement receptors on their surfaces and can thus bind all three components of an immune complex. In addition to the direct effects that they exert on cells, immune complexes may affect localization, presentation and digestion of antigen. In this article, Birgitta Heyman discusses recent developments in antibody-mediated regulation of the humoral immune response, with emphasis on in vivo systems where antigens are injected together with highly purified IgM or IgG antibodies in the absence of adjuvants.

Comparison of diversity and function of house dust mite-specific T lymphocyte clones from atopic and non-atopic donors

Panels of CD4+CD8- T lymphocyte clones (TLC), specific for house dust mite Dermatophagoides pteronyssinus (Dp) proteins, were generated from the peripheral blood of an atopic Dp-allergic donor (AD), suffering from severe atopic dermatitis, and a histocompatible non-atopic donor (NAD). We studied the diversity of TLC within these two panels in search for the possible occurrence of dominant clone types with properties that might be characteristic for the atopic or non-atopic state. TLC with specificities for at least four different Dp proteins were found within the panel from AD "L" and for at least three different Dp proteins within the panel from NAD "K". In addition, both panels showed a considerable but comparable restriction diversity within HLA-DR. Despite the diversity within the panels, all Dp-specific TLC from AD were found to produce IL 4, after HLA class II-restricted Dp-specific stimulation, whereas the TLC from NAD produced no or only minimal amounts of this lymphokine. Only supernatants from stimulated AD TLC could induce IgE secretion by B cells from NAD. Conclusively, these observations do not give evidence for the occurrence of an abnormal Dp-specific T cell repertoire in AD, but rather suggest aberrant secretion of the IgE-inducing lymphokine IL 4 by CD4+ Dp-specific T cells from AD.

Defective in vitro production of gamma-interferon and tumor necrosis factor-alpha by circulating T cells from patients with the hyper-immunoglobulin E syndrome

Circulating T cells from four patients with the hyper-IgE syndrome were found to produce significantly lower concentrations of interferon-gamma (IFN-gamma) in response to stimulation with phytohemagglutinin (PHA) than did T cells from eight age-matched healthy controls, three patients with atopic dermatitis and one patient with chronic granulomatous disease. A clonal analysis revealed that patients with hyper-IgE syndrome had markedly lower proportions of circulating T cells able to produce IFN-gamma and tumor necrosis factor-alpha (TNF-alpha) in comparison with controls. In contrast, the proportions of peripheral blood T cells able to produce IL-4 or IL-2 were not significantly different in patients and controls. All the four patients with hyper-IgE syndrome showed high proportions of circulating CD4+ helper T cells able to induce IgE synthesis in allogeneic B cells, as well. Such an activity for IgE synthesis appeared to be positively correlated with IL-4 production by T cells and inversely related to the ability of the same T cells to produce IFN-gamma. Since IFN-gamma exerts an inhibitory effect on the synthesis of IgE and both IFN-gamma and TNF-alpha play an important role in inflammatory reactions, we suggest that the defective production of IFN-gamma may be responsible for hyperproduction of IgE and the combined defect of IFN-gamma and TNF-alpha may contribute to the undue susceptibility to infections seen in patients with hyper-IgE syndrome.

Role of interleukins in induction and regulation of human IgE synthesis

Studies of human IgE synthesis are summarized and provide further insight into the cellular and molecular mechanisms involved in IgE regulation, as well as in the alterations responsible for IgE disregulation in some pathological conditions. These include the demonstration that IL-4 is the essential factor for the induction of human IgE syntheses. Another T cell-derived lymphokine, IFN-gamma negatively regulated the IgE synthesis induced by IL-4. These two lymphokines can be produced by different T helper cells, as shown in mice, but they can also be the product of the same T cells clones. Additional cellular and/or molecular signals appear to be involved in the IL-4-induced IgE synthesis, but their precise role in this process is undetermined. Finally, alternations of one or more of these regulatory mechanisms can be detected in patients with pathological conditions characterized by hyperproduction of IgE. In particular, the increased prevalence of T cells clones able to produce IL-4 appears to be a distinctive feature of patients with common atopy whereas a reduction in the proportion of IFN-gamma-producing T cells seems to be peculiar of both patients with hyper-IgE syndrome and patients with AIDS.

Immunoregulation in clinical diseases: an overview

The quality, magnitude, and persistence of each immune response results from the net balance of different influences that may amplify or decrease it. The complex interaction between such influences underlies the concept of immunoregulation. Comprehension of the complex mechanisms of immunoregulation has the potential to yield important insights into the genetic and the molecular basis of the physiology of immune responses and of the pathophysiology of a wide number of clinical diseases. The principal basic mechanisms of immunoregulation comprise the systems of recognition structures regulating antigen specificity of immune responses and the interconnecting systems involved in the overall regulation of immune responses. Such regulatory interconnecting systems include regulatory T cells, idiotypic network, isotopic network, and the intricate web of interactions between cytokines (cytokine network). In addition, there is now evidence that these highly complex and sophisticated regulatory systems are not only interrelated to each other, but are themselves regulated by signals originated outside the immune system (e.g., from the nervous or the endocrine apparatus). These alterations of immunoregulatory mechanisms are involved in the pathogensis of many groups of human diseases, such as immunodeficiencies, neoplastic and immunoproliferative disorders, many infectious diseases, atopic disease, and autoimmune disorders. A rational knowledge of immunoregulation will hopefully have great practical implications for future strategies of diagnosis and treatment of diseases in which deranged immune functions play a major role.

IgE production by normal human lymphocytes is induced by interleukin 4 and suppressed by interferons gamma and alpha and prostaglandin E2

The effect of human recombinant interleukin 4 (IL-4) on antibody production by normal peripheral blood mononuclear cells enriched for B cells was investigated. IL-4 preferentially induced IgE synthesis in vitro. In addition, a low induction of IgG production was observed, whereas IL-4 had no effect on IgA and IgM synthesis. The IL-4-induced IgE production by B cells required T cells and monocytes but was specifically inhibited by an anti-IL-4 antiserum indicating that, although IL-4 acts indirectly, it is responsible for the induction of IgE synthesis. IL-4-induced IgE production was blocked in a dose-dependent way by interferon gamma (IFN-gamma), interferon alpha (IFN-alpha), and prostaglandin E2. IFN-gamma also inhibited IL-4-induced IgG production. These inhibitory effects of IFN-gamma and IFN-alpha on IgE production cannot be attributed to toxic effects since IFN-alpha induced IgM production in the presence of IL-4, whereas IFN-gamma was ineffective in inhibiting IgG production induced by IL-2. IFN-gamma, IFN-alpha, and prostaglandin E2 also inhibited IL-4-induced expression of the low-affinity receptor for the Fc portion of IgE (CD23) on B cells, indicating that there is an association between CD23 expression and IL-4-induced IgE production. This theory was supported by the finding that IL-4-induced IgE production was inhibited by F(ab')2 fragments of an anti-CD23 monoclonal antibody.

Profiles of lymphokine activities and helper function for IgE in human T cell clones

A large panel of phytohemagglutinin (PHA)-induced T cell clones (690 in total), established from four different human lymphoid tissues (peripheral blood, tonsils, lymph nodes and spleens) by a high-efficiency cloning technique, was characterized according to their pattern of lymphokine production. The majority of both CD4+ and CD8+ clones from all lymphoid tissues produced interleukin (IL) 2 and/or interferon (IFN)-gamma in response to 24-h stimulation with PHA. In contrast, higher proportions of IL 4-producing clones were found among CD4+ clones from tonsils and spleens than from peripheral blood and lymph nodes, whereas only a minority of CD8+ clones from all lymphoid tissues were found to produce IL 4. It was not possible to divide the CD4+ (helper/inducer) clones on the basis of their pattern of lymphokine activity into two clear-cut groups analogous to Th1 and Th2 helper clones described in mice. Although 21 out of 503 (4%) CD4+ T cell clones produced IL 4, but not IFN-gamma or IL 2, and 208 (41%) produced IL 2 and/or IFN-gamma, but not IL 4, a total number of 185 (37%) CD4+ clones showed the ability to produce IL 4 plus IL 2 and/or IFN-gamma. All types of CD4+ T cells (as classified according to their pattern of lymphokine activity) provided help for IgG production in allogeneic B cells. In contrast, helper function for IgE was detectable only among the IL 4-producing clones.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of interleukin-4 in the induction of human IgE synthesis and its suppression by interferon-gamma

Supernatants (SN) from 10 phytohemagglutinin (PHA)-stimulated human T cell clones (TCC), selected for their helper function on IgE synthesis, were found to provide IgE helper activity in atopic B cells showing low or undetectable spontaneous in vitro IgE synthesis. In contrast, SN from 5 PHA-stimulated TCC unable to provide helper function for IgE synthesis consistently failed to elicit IgE production. SN active on IgE synthesis contained high concentrations of interleukin-4 (IL-4), whereas inactive SN did not contain detectable amounts of IL-4. Moreover, the IgE helper activity of TCC SN was strongly inhibited by the addition of interferon-gamma (IFN-gamma) to B cell cultures. These data suggest that IL-4 may play a role in the induction of in vitro human IgE synthesis, whereas IFN-gamma displays an inhibitory effect.