Mofecu/m Immsmology, Vol. 17, pp. 1033-1038. Pergamon Press Ltd. 1980. Printed in Great Britain. FINE SPECIFICITY AND IDIOTYPE ANALYSIS OF THE IgE RESPONSE TO THE SYNTHETIC TERPOLYMER L-GLUTAMIC ACID60-~-ALANINE30-~-TYROSINE10 (GAT) AND ITS DINITROPHENYL CONJUGATE (DNP-GAT)* ILANA LOWY,’ ANNIEPROUVOST-DANON, ANNIEABADIE3 and JACQUES THl??ZE2 ‘Unite d’lmmunothtrapie Exptrimentale, and ZUnite d’Immunochimie Analytique, Institut Pasteur, 28, rue du Docteur Roux, 75724 Paris Cedex 15, France, and 31NSERM U-131, 92140 Clamart, France zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO (Received 19 December 1979) Abstract-In three mouse strains, BALB/c, CBA and C3HjHe, specific IgE antibodies could be induced by DNP-GAT and GAT. The presence of both anti-GAT and anti-DNP IgE antibodies was measured, using both heterologous PCA in rats and specific degranulation of peritoneal mast cell tests. The fine specificity of the IgE anti-GAT antibodies elicited by both DNP-GAT and GAT was similar to the specificity of anti- GAT IgG antibodies. The I@ anti-GAT antibodies cross reacted with L-glutamic acidSo-L-tyrosinesO (GT) copolymer, but not with r_-glutamic acid 60-L-alanine (GA) copolymer. Anti-idiotypic serum was found to be able to degranulate specifically peritoneal mast celfs from GAT and DNP-CAT immunized animals, indicating that IgG and IgE anti-GAT antibodies share common idiotypic determinants. INTRODUCTION A substantial amount of information has been accumulated concerning the immune response to the terpolymer of L-glutamic acid60-r_-aIanine30- r.,-tyrosine’O (GAT). At the cellular level, helper and suppressor cells, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA as well as specific suppressor factors, have been characterized (Kapp et al., 1974; Theze et al,, 1977). At the antibody level, we have characterized an anti- idiotypic antiserum specially directed against GAT idiotypic specificities expressed by BALB/c mice (Theze & Moreau, 1978; Theze & Sommt, 1979). The genetic distribution of the corresponding GAT idiotype has been reported (Theze & Somme, 1979). We have demonstrated both by isoelectrofocalization and two dimensional polyacrylamide gel electrophoresis that the anti-GAT response is of very restricted heterogeneity (Petit et al., 1979). More recently, we have undertaken to study the isotype control of the anti-GAT response. Results have been obtained concerning the control of expression of IgG, anti-DNP response induced by DNP-GAT in various strains (Seman & Theze, ~npubIished *This study was supported by research grant No. 77-7-1378 from the Delegation Get&ale a la Recherche Scientifique et Technique and by research grant No. 77-507 fro-m the Direction des Recherches, Etudes et Techniques, Minis&e de la Defense, Paris, France. results). With this background we felt that the investigation of the IgE response against GAT and its dinitrophenyl conjugate GAT-DNP should provide additional infor- mation concerning the immune response to GAT. In this communication we report the existence of a specific EgE response in GAT or DNP-CAT primed animals. This class of antibody was demonstrated by both passive cutaneous anaphylaxis (PCA) and by antigen-specific degranulation of peritoneal mast cells. The pattern of cross reactivity displayed by IgE anti- GAT antibodies resembles that of the IgG anti- GAT antibodies; therefore we have investigated the presence of common idiotypic determinants between IgE and IgG anti-GAT antibodies. MATERIALS AND METHODS Animals C3H/He, CBA and BALB/c mice, 6-8 weeks old of both sexes, were obtained from the Centre National de la Recherche Scientifique, Orleans, France. Sprague-Dawley male rats were used for the PCA test. Antigens DNP,-ovalbumin (DNP-OVA) was prepared 1033