INDUCTION AND DIFFERENTIAL REGULATION OF BEE VENOM PHOSPHOLIPASE A(2)-SPECIFIC HUMAN IGE AND IGG(4) ANTIBODIES IN-VITRO REQUIRES ALLERGEN-SPECIFIC AND NONSPECIFIC ACTIVATION OF T-CELL AND B-CELL

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-s pecific IgE antibody production, we have established a culture system that allows the generation of bee venom phospholipase A(2)-specific Ig E and IgG, antibodies. Allergen-specific IgE was induced by simultaneo usly activating T cells and B cells specifically with allergen and pol yclonally with anti-CD2 and soluble CD40 ligand in the presence of IL- 4. Additional stimulation of T cells through the CD2 activation pathwa y by two different anti-CD2 monoclonal antibodies enhanced both the al lergen-specific and the total IgE and IgG(4) responses. An optimal amo unt of allergen (0.1 ng/ml) resulted in the induction of both allergen -specific IgE and IgG(4) antibodies. Higher antigen doses reduced alle rgen-specific antibodies and enhanced total isotype production. This d ifferential regulation of allergen-specific and total isotypes reflect s different allergen dose-dependent mechanisms in specific and polyclo nal activation of T and B cells. Although both isotypes require IL-4 f or initial induction, opposite regulatory effects by T cells were obse rved for IgE and IgG(4) antibody expression. In peripheral blood monon uclear cell cultures stimulated with soluble CD40 ligand, IL-4, and ph ospholipase A(2), stimulation of T cells with higher amounts of anti-C D2 enhanced IgG(4) 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 IgG (4) by antigen concentration and demonstrate the pivotal role of T cel ls controlling the synthesis of the IgE and IgG(4) antibody isotypes.