Induction and differential regulation of bee venom phospholipase A2-specific human IgE and IgG4 antibodies in vitro requires allergen-specific and nonspecific activation of T and B cells.

Investigations on the mechanisms of IgE regulation in vitro have been conducted thus far in systems that allow the synthesis of total rather than specific IgE. To study the regulatory prerequisites of antigen-specific IgE antibody production, we have established a culture system that allows the generation of bee venom phospholipase A2-specific IgE and IgG4 antibodies. Allergen-specific IgE was induced by simultaneously activating T cells and B cells specifically with allergen and polyclonally with anti-CD2 and soluble CD40 ligand in the presence of IL-4. Additional stimulation of T cells through the CD2 activation pathway by two different anti-CD2 monoclonal antibodies enhanced both the allergen-specific and the total IgE and IgG4 responses. An optimal amount of allergen (0.1 ng/ml) resulted in the induction of both allergen-specific IgE and IgG4 antibodies. Higher antigen doses reduced allergen-specific antibodies and enhanced total isotype production. This differential regulation of allergen-specific and total isotypes reflects different allergen dose-dependent mechanisms in specific and polyclonal activation of T and B cells. Although both isotypes require IL-4 for initial induction, opposite regulatory effects by T cells were observed for IgE and IgG4 antibody expression. In peripheral blood mononuclear cell cultures stimulated with soluble CD40 ligand, IL-4, and phospholipase A2, stimulation of T cells with higher amounts of anti-CD2 enhanced IgG4 in parallel to increased IL-2 and interferon-gamma secretion but inhibited IgE synthesis. These results provide evidence for differential regulation of allergen-specific and total IgE and IgG4 by antigen concentration and demonstrate the pivotal role of T cells controlling the synthesis of the IgE and IgG4 antibody isotypes.