José M. Carballido

Determinants and Mechanisms of Human Immune Responses to Bee Venom Phospholipase A2

The elicitation of an immune response to protein antigens depends on the specific recognition of antigenic determinants (epitopes) by T and B lymphocytes. Bee venom phospholipase A2 (PLA) represents the major antigen/allergen of honey bee venom. It displays three dominant immunogenic peptide and one glycopeptide T cell recognition sites. These epitopes are equally recognized by both allergic and nonallergic individuals. A mixture of the three epitope containing peptides was successfully used in specific immunotherapy of bee venom–allergic patients. Both peptide and whole bee venom immunotherapy induced a state of specific anergy in T cells. The production of specific IgE and IgG4 antibodies directly correlated with the secreted interleukin–4:γ–interferon (IL–4:IFNγ) ratio, which itself depended on the concentration of available antigen and the strength of the T cell–activating signal. This signal comprises accumulated molecular interactions delivered by engagement of the antigenic peptide/MHC class II complex with the T cell receptor (TcR). Indeed the thermodynamic laws of chemical equilibrium reactions reveal that the antigen concentration, together with the equilibration constant Ki and the related Gibbs standard free energy ΔG° of the MHC–II/Ag/TcR complex reaction, may govern the secreted IL–4:IFNγ ratio, and in consequence, differential IgE and IgG4 antibody formation. Ki includes epitope and MHC–II haplotype variability and therefore represents a measure of immunological individuality. A major B cell epitope was determined by using point–mutated PLA. Specific antigen recognition by B cells can trigger distinct cytokine profiles in T cells and contribute to the differential regulation of specific IgE and IgG4 antibodies. Our results indicate that distinct cytokine profiles inducing allergic and nonallergic responses can be attributed to thresholds of T cell activation generated by the specific binding properties of individual MHC–II molecules to immunogenic T cell epitopes and their presentation to TcR.

Human monoclonal or polyclonal antibodies recognize predominantly discontinuous epitopes on bee venom phospholipase A2

BACKGROUNDnTwo hybridomas, which secrete human monoclonal antibodies of IgG4 isotype specific for the main bee venom antigen/allergen phospholipase A2, were generated. The antigenic determinants recognized by these antibodies were mapped and compared with the binding sites of murine monoclonal and human polyclonal antibodies raised against the same antigen.nnnMETHODSnTwo hybridomas were developed by fusing heteromyelomas to Epstein-Barr virus immortalized B cells obtained from beekeepers. The cloned hybridomas were stable and secreted up to 40 mg/L of antibody into the culture supernatant. Phospholipase A2 specificity of the human monoclonal antibodies was confirmed by binding and inhibition ELISA and by Western blot analysis. Epitope mapping on phospholipase A2 was done with the PEPSCAN method and ELISA techniques.nnnRESULTSnThe epitopes recognized by the human monoclonal antibodies were shown to be discontinuous and did not contain the sugar residue. Similar results were obtained with polyclonal antibodies of IgG4 isotype (from beekeepers) specific for phospholipase A2, which could also inhibit the binding of the human monoclonal antibodies to phospholipase A2. In contrast, antigen binding of the human monoclonal antibodies could not be inhibited by murine monoclonal antibodies against bee venom phospholipase A2.nnnCONCLUSIONSnThe data indicate that the human monoclonal antibodies obtained are representative of a part of the polyclonal immune response to phospholipase A2 from beekeepers and may allow a more precise analysis of the humoral immune response to phospholipase A2 that is associated with protection.

Inhibition of Human IgE Synthesis in vitro and in SCID-hu Mice by an lnterleukin-4 Receptor Antagonist

In the present study, it is shown that a human interleukin (IL)-4 mutant protein (IL-4.Y124D) acts as a potent IL-4 and IL-13 receptor antagonist. Human (h) IL-4.Y124D efficiently inhibits both IL-4- and IL-13-induced IgE production in vitro. In addition, hIL-4.Y124D strongly inhibits ongoing human IgE synthesis in SCID-hu mice. These inhibitory effects are specific, since human IgG levels were not significantly affected. These results confirm the notion that the IL-4 and IL-13 receptor share a common component, which is required for signal transduction. In addition, they show that relatively large antagonistic polypeptides, such as hIL-4.Y124D have potential clinical utility in reducing IgE-mediated allergic diseases.

Regulation of the Cytokine Production of Allergen-Specific Human T-Cell Clones by the Allergen

Human T-cell clones to bee venom phospholipase A2 (PLA), isolated from allergic, hyposensitized and hyperimmune individuals to bee sting, secrete both IL-4 and IFN-γ after antigen stimulation. However