Immunological responsiveness of neonatal A/J mice to isotypic determinants of syngeneic IgE

Generalization of single immunological experiences by idiotypically mediated clonal connections

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

Peptides derived from IgE heavy chain constant region induce profound IgE isotype-specific tolerance

(BALB/c x SJL)F1 mice, perinatally injected with peptide-N-glyconase F-treated, deglycosylated IgE heavy chain or recombinant IgE heavy chain (CH epsilon 2-CH epsilon 4), were profoundly inhibited in antigen-specific IgE production. There exist minimally two tolerogenic IgE peptides, residing in the CH epsilon 2 and CH epsilon 4 domains. Peptide I, generated by V8 protease, comprises 39 amino acids within CH epsilon 2, beginning at amino acid 103. Peptide E begins at amino acid 312 of the CH epsilon 4 domain and extends through the CH epsilon 4 domain. The total lack of antigen-specific IgE responses in IgE peptide-treated mice was not due to overproduction of interferon-gamma, nor lack of interleukin (IL)-4, as predicted by the Th2/IL-4 paradigm for IgE production. IgE-tolerant mice exhibited comparable levels of circulating anti-IgE antibodies to those of PBS-treated control mice. IgG obtained from sera of both sources failed to inhibit IgE responses in vitro. Moreover, IgE responses of spleen cells from IgE peptides-treated mice were restored by CD4+ T cells from PBS-treated control mice. We hypothesize that regulation of antigen-specific IgE responses is mediated by CD4+ T cells which normally recognize IgE peptides on IgE precursor B cells, and can be rendered tolerant by perinatal IgE peptide treatment.

Is vaccination against IgE possible?

A substantial reduction in the levels of both total and antigen specific IgE will most likely result in improved symptom scores in atopic individuals. Based on this assumption we initiated a project to study the possibility of reducing levels of circulating and mast cell bound IgE, by inducing a strong autoimmune antibody response against IgE in the host. Bacterially produced fusion proteins containing constant domains two (CH2) and three (CH3) of rat IgE directly linked to the glutathione-S-transferase (GST) protein from Schistosoma japonicum or to the maltose binding protein of Esherichia coli were used as the active components of the allergy vaccine. Injection of either of these fusion proteins together with adjuvant led to the induction of a strong autoimmune anti-IgE response in several IgE low or medium responder strains of rats. Vaccination of ovalbumin sensitised Wistar rats with the GST-C2C3 fusion protein resulted in a profound decrease in serum IgE levels and later in a nearly complete block in histamine release from mast cells and basophils upon challenge with either a cross-linking polyclonal anti-IgE antiserum or a specific allergen. This shows that it is possible to reduce IgE levels in an animal to such an extent that it gives a clear clinical effect. Recent studies with an extended panel of rat strains including four IgE high responder strains, indicate that induction of the autoimmune response is dependent on the plasma concentration of IgE before vaccination. A high concentration of IgE has a negative effect on the induction of autoimmunity, most likely by inducing a B-cell tolerance in the host. Vaccinated subjects with very high IgE concentrations thereby responds poorly to the vaccine. Current studies are aimed at overcoming this potential limitation of the vaccination procedure.

Prolongation of the responsiveness of newborn mice to syngeneic IgE by inhibition of IgE synthesis

Between the ages of 2 to approximately 11 days mice respond to a challenge with syngeneic IgE by producing anti-IgE antibodies; by the age of 2 weeks they are unresponsive. Even adult mice, however, produce high titers of anti-IgE antibodies when immunized with a conjugate of syngeneic IgE and a foreign antigen such as keyhole limpet hemocyanin (KLH), indicating that adult tolerance to unconjugated IgE resides in the T-cell compartment. The loss of responsiveness in 2-week-old mice follows closely after the first appearance of IgE-secreting cells and detectable serum IgE. This suggests that the delayed onset of tolerance is attributable to the delay in synthesis of IgE. Data presented here provide support for this hypothesis. A further delay in the initial synthesis of IgE, induced by neonatal administration of anti-IgM antibodies, caused a corresponding extension of the period after birth during which mice remain responsive to unconjugated IgE.

Efficient production of syngeneic anti-IgE monoclonal antibodies with high affinity and diverse specificity

Syngeneic monoclonal anti-IgE antibodies are of value in studies of the suppression of IgE synthesis. Procedures are described here for the production of high titers of murine anti-IgE antibodies by initiating immunization in the perinatal period, before mice develop tolerance to their autologous IgE. This in turn facilitates the production of monoclonal anti-IgE antibodies. Properties of some of these mAbs are reported, including affinity, fine specificity and ability to bind to IgE on B lymphoma cells or mast cells.

Role of antibody and T cells in the long-term inhibition of IgE synthesis

We have shown that the long-term inhibition of IgE synthesis associated with perinatal inoculation of syngeneic IgE is accompanied by the synthesis of autoantibodies to IgE. Synthesis of IgE can also be inhibited by passive transfer of syngeneic anti-IgE antibodies. In the present investigation we made use of adoptive transfer experiments to assess the relative roles of antibodies and T cells in the inhibitory process. It was found that spleen cells from IgE-suppressed mice (synthesizing anti-IgE antibodies) could adoptively transfer the state of inhibition to syngeneic adult mice. The inhibition occurred only under conditions in which the recipient mice synthesized anti-IgE antibodies. Separated B cells, CD4+ T cells, CD8+ T cells, or a mixture of B and CD8+ T cells were ineffective. However, strong inhibition of IgE synthesis (as indicated by serum levels and numbers of IgE-secreting cells in the spleen) was observed after transfer of a mixture of B cells and CD4+ (helper) T cells. The results indicate that in this experimental model anti-IgE antibodies are the suppressive agent and that T cells do not play a role other than that of providing help to B cells for anti-IgE synthesis.

Tolerance to self and the processing and presentation of self antigens

Antigen processing and presentation is critical to the generation and maintenance of self tolerance. The hemoglobin system has provided important data on self antigen processing and presentation in vivo. Hemoglobin/Ia complexes were detectable in the thymus before the time of positive and negative selection. In addition, thymic epithelial cells were shown to lack the costimulatory factors necessary to trigger T cell clone proliferation. We have extended these findings to the renal proximal tubule. This class II MHC-expressing epithelial cell was demonstrated to process and present foreign as well as self antigens to T cell hybridomas. Current studies are examining whether this epithelial cell possesses the costimulatory factors required to fully stimulate T cell clones, or whether the proximal tubule may play an important role in the maintenance of self tolerance. In addition we describe the exciting model of murine autoimmune myocarditis. We have demonstrated that this is a T cell mediated disease and believe that cardiac antigen presenting cells constitutively process and present the inciting self antigen, myosin. These studies may provide important insights into autoimmunity and self tolerance.

IgE-secreting cells in the thymus: correlation with induction of tolerance to IgE

We have shown previously that normal mice become tolerant to endogenous IgE when they are approximately 2 weeks old and that this corresponds closely with the initial appearance of IgE in serum. Tolerance evidently is restricted to T cells, since B cells responsive to IgE are present in neonatal and adult mice. The present report shows that IgE-secreting cells can be detected in the thymus between days 7 and 11 after birth and that the onset of tolerance to IgE occurs at the age of 11 days. Similar results were obtained in A/J and (BALB/c x A/J)F1 mice. This suggests that tolerance is induced in the thymus, probably by cells bearing peptide fragments of IgE. The order of appearance of IgE-secreting cells is thymus, spleen, and mesenteric lymph nodes.

Genesis of host IgE competence: perinatal IgE tolerance induced by IgE processed and presented by IgE Fc receptor (CD23)-bearing B cells

A murine model for studying life-long IgE tolerance was previously developed in this laboratory by perinatal IgE injection into neonates. Herein, we demonstrated that normal and immortal CD23+ B cell lines presented processed IgE via CD23-mediated endocytic pathway and triggered perinatal IgE tolerance. The observations were as followed: (a) CD23 on normal B cells or B cell hybridomas mediated IgE-dependent perinatal IgE tolerance and total IgE deficiency; and lack of either antigen-specific IgE or total IgE did not correlate with elevated levels of autologous anti-IgE in individual mice; (b) IgE tolerance-inducing capacity of CD23+ B cell hybridomas was augmented by treatment with antigen-IgE complexes or interleukin 4, and significantly inhibited by anti-CD23 prior to IgE pulsing; (c) antigen-IgE complexes were endocytosed and degraded in acid hydrolases-containing vesicles; and IgE tolerance was abrogated by treating IgE-pulsed 17A11 at 4 degrees C or 20 degrees C followed immediately by fixation, and by treating IgE-pulsed 17A11 with metabolic inhibitors that elevated intracellular pH of the endocytic vesicles. In conclusion, this study suggested that one pivotal step of genetic control of IgE responses may be exercised at the early developmental stage of T cells of the IgE lineage, and that CD23 may facilitate capture of endogenously secreted IgE, and mediate endocytic processing and presentation of self IgE epitope(s), and thus contribute to the genesis of host IgE competence.

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.

Mechanisms of IgE tolerance: dual regulatory T cell lesions in perinatal IgE tolerance

The mechanisms of genetic control of IgE responses are exercised at different immuno-physiological levels. This study centered upon the development of IgE lineage-specific regulatory T cells. Herein, we demonstrate the following points: (a) perinatal administration of soluble self IgE molecule or self IgE complexed with foreign antigen induces IgE tolerance as manifested by antigen-specific IgE unresponsiveness and a generalized IgE immunodeficiency, and the induction of IgE tolerance does not affect antigen-specific IgG1, IgG, and IgA responses; (b) inducibility of perinatal IgE tolerance is correlated with complete absence of endogenously secreted IgE in the neonates; and the state of persistent IgE tolerance also does not correlate with the presence of high levels of circulating anti-IgE autoantibodies; (c) The lesions induced during the ontogeny of IgE antibody system do not appear to result from an imbalance of production of interleukin 4 and interferon-gamma by T helper Th2 and Th1 cells in antigen-stimulated cultures; the dual immunoregulatory lesions in T cell subsets are demonstrated: clonal anergy/deletion of CD4+ IgE Th cells and the presence of CD8+ IgE suppressor cells induced by perinatal IgE treatment. We propose that antigen/interleukin 4 activated B cells are controlled by IgE lineage-specific regulatory T cells which recognize self IgE determinant(s) on IgE committed B cells. Life-long IgE tolerance ensues as a result of a new steady state of IgE lineage-specific CD4+ and CD8+ T cell subsets.

Inhibition of IgE synthesis by anti-IgE: role in long-term inhibition of IgE synthesis by neonatally administered soluble IgE

Inoculation of syngeneic IgE into 2- to 12-day-old mice results in prolonged synthesis of anti-IgE antibodies without further challenge. These anti-IgE antibodies may be largely responsible for the long-term inhibition of synthesis of IgE that is known to result from a perinatal challenge with IgE. This conclusion is supported by the effect of passive inoculation of syngeneic polyclonal anti-IgE antibodies into young mice, which similarly results in selective inhibition of IgE synthesis. Further evidence is the close relationship between the age dependency of IgE-induced inhibition of subsequent IgE synthesis and the ability of IgE to induce anti-IgE antibodies. IgE synthesis was monitored at the level of secretion by B cells as well as serum IgE levels and IgE antibody responses.