ACTIVATION AND HAPTEN INHIBITION OF MAST-CELLS SENSITIZED WITH MONOCLONAL IGE ANTI-PENICILLIN ANTIBODIES - EVIDENCE FOR 2-SITE RECOGNITION OF THE PENICILLIN DERIVED DETERMINANT

We utilized an in vitro mast cell activation assay and hapten inhibiti on of mediator release to characterize the fine specificity of two IgE anti-penicillin monoclonal antibodies (mAb). Cultured mouse mast cell s were passively sensitized with IgE mAb anti-benzylpenicillin (f3P) o r anti-amoxicillin (AX) and challenged with a range of penicillin-huma n serum albumin (IISA) conjugates. Mast cells sensitized with IgE anti -BP degranulated in response to BP-IISA, but not to AX-HSA or ampicill in(AMP)-HSA, whereas mast cells sensitized with IgE anti-AX responded to AX-HSA but not to BP-HSA or AMP-WSA. Because BP, AX and AMP differ chemically only in the structure of their side chain, these results sh ow that this part of the drug molecule is essential for recognition by IgE antibody. Unexpectedly, although IgE-sensitized mast cells respon ded to only one penicillin in protein-conjugated form, antigen-induced degranulation was inhibited by the monomeric derivative of more than one penicillin. Furthermore, antigen activation of IgE-sensitized cell s was inhibited, although less potently, by haptens representative of the specific penicillin side chain or the binuclear portion of the dru g molecule. These patterns of recognition and hapten inhibition were a lso seen in solid-phase enzyme-linked immunosorbent assay (ELISA), alt hough all haptenic inhibitors were approximately 100 times less potent in the ELISA compared to the mast cell assay. To explain these findin gs we propose a model in which IgE binding to penicillin-protein antig en is dependent on recognition of two distinct epitopes on the drug mo lecule: the first comprising the side chain, and the second comprising the binuclear portion plus the proximal region of the side chain. Thi s two-site hypothesis provides a generally applicable model of antibod y recognition of penicillins and provides a rational basis for underst anding the specificity and cross-reactivity of IgE-mediated allergic r eactions to penicillins.