Immunodominance of conformational epitopes over linear ones in four proteins was quantified making use of the B-cell hybridoma technology. The proteins were immunized in their native forms into BALB/c mice, and clonal frequencies of B-cell hybridomas that produce antibodies to the native and denatured forms were determined, using ELISA and immunoblotting. All 16 monoclonal antibodies (mAbs) to Porphyromonas gingivalis fimbria were suggested to recognize conformational epitopes expressed by the oligomer. Ten out of 14 mAbs to Serratia marcescens fimbria and 13 of 15 mAbs to hen lysozyme were also specific to their conformational epitopes. In contrast, all 18 mAbs to a surface protein of Streptococcus mutans, termed PAc, reacted to both the native and denatured forms, thereby indicating the immunodominance of linear epitopes in this protein. The results suggest that B-cell epitopes of proteins possessing stable tertiary or quaternary structures are predominantly expressed by the higher-order structures. (C) 2003 Elsevier Inc. All rights reserved.