Induction of human in vitro IgE synthesis via stimulation by anti-CD3 antibody

A specific feedback by anti-IgE autoantibodies on the cytokine network in allergy

During recent years we have shown that anti-IgE antibodies can have different biological functions. Depending on their epitope specificity they can be anaphylactogenic or not, they interfere with IgE binding to its receptor or not, and they enhance or inhibit IgE synthesis. Therefore we propose a theoretical model implying that anti-IgE autoantibodies are specific feed back molecules that neutralize IgE induced by the cytokine network. In the normal individual this system would be beneficial, where as the atopic individual, due to differences in its B cell repertoire, will produce the wrong type of anti-IgE antibody. The wrong type of anti-IgE antibody may even aggravate the disease as some of these autoantibodies may induce IgE synthesis or trigger effector cells that in turn generate a Th2 like cytokine pattern.

Human transferrin allows efficient IgE production by anti-CD3-stimulated human lymphocytes at low cell densities

A solid-phase-coupled anti-CD3 T cell activation system was used to study the regulation of human IgE production in vitro. Using 5000 peripheral blood lymphocytes from healthy donors, containing 10%-20% B lymphocytes and no monocytes. IgE was produced very efficiently on a per cell basis. A key observation was that apart from interleukin (IL) 4, human transferrin was essential for IgE production. Furthermore it was found that IgE was produced at low densities only; at higher cell concentrations IgE production was completely abrogated, whereas IgM production increased with increasing cell density. This inhibition at higher cell densities is probably mediated by IL2. Addition of low amounts (6 U/ml) of IL2 strongly enhanced IgE and IgM production at low cell densities, but higher concentrations of IL2 (50 U/ml) were strongly inhibitory for IgE production.

Cytokine mRNA levels in antigen-stimulated peripheral blood mononuclear cells

Levels of cytokine mRNA coding for granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-gamma (IFN-gamma), interleukin (IL) 2, IL 1 beta, IL 4 or IL 6 have been measured by Northern blot analysis after antigen stimulation. As source for RNA we used peripheral blood mononuclear cells (PBMC) from donors which showed a proliferative response after tetanus toxoid or Candida albicans stimulation. For comparison PBMC were also stimulated with lectins and anti-CD3 antibody. With some variations among donors, antigens clearly induced measurable levels of IFN-gamma, GM-CSF and IL 2 mRNA. Increased levels for IL 6 were also detected after antigen stimulation. In contrast to polyclonal T cell stimuli, antigens showed delayed kinetics of mRNA steady-state levels and resembled in this respect more closely the stimulation with pokeweed mitogen. Thus, cytokine mRNA levels may be assessed in unfractionated PBMC after antigen stimulation. The two tested antigens also clearly show a cytokine pattern distinct from that induced in polyclonal stimulations such as anti-CD3.

Detection of individual interleukin 2-producing cells after anti-CD3 antibody activation

A new intracytoplasmic immunofluorescence staining technique to detect and quantify human interleukin-2 (IL-2)-producing lymphocytes is described. Blood mononuclear cells (MNC) were cultured and stimulated by mitogenic anti-CD3 antibody to produce IL-2. The cells were then fixed and subsequently permeabilized in suspension by the detergent saponin. Cytoplasmic IL-2 could then be demonstrated using polyclonal IL-2 specific antibodies and indirect immunofluorescence staining. A characteristic morphology of the IL-2 staining was noted with a local circle-shaped accumulation in the cytoplasm in a perinuclear position, probably reflecting the presence of the lymphokine in the Golgi stacks. A rapid, but transient IL-2 production peak 6 h after initiation of the cultures was observed. Only 1% of the cells produced IL-2, but each IL-2 stained cell was very bright, indicating a low capacity of anti-CD3 antibody to induce IL-2 production rather than an insensitivity of our detection system. Of the IL-2-producing cells 90% were CD4-positive T cells and 10% were CD8-positive T cells as revealed by two-colour staining of cell surface antigens and cytoplasmic IL-2.

Effect of recombinant human interleukin 4 on spontaneous in vitro human IgE synthesis

Recombinant human interleukin 4 (IL 4) alone enhanced the spontaneous IgE synthesis in cultures of peripheral blood leukocytes (PBL) from atopic patients as well as from nonatopic individuals, suggesting the existence of preactivated PBL sensitive for IL 4. Preactivated cells were also obtained by stimulation with Staphylococcus aureus strain Cowan I (SAC). However, co-stimulation of PBL by IL 4 with SAC or anti-IgM antibody and pokeweed mitogen did not result in an enhanced IgE synthesis. Optimal IL 4 concentrations for the induction of IgE synthesis coincided with optimal proliferative responses in PBL. The effect of IL 4 was not isotype specific, and in terms of protein even more IgG and IgM antibodies were formed. The effect of IL 4 on IgE synthesis was counteracted by very low concentrations of interferon-gamma (IFN-gamma), suggesting that both IL 4 and IFN-gamma might be decisive cytokines for the human in vitro IgE synthesis.