Idiotope mapping on the variable region of an antibody clonotype produced by normal (nonmalignant) human B cells.

Human anti-N-acetyl-D-glucosamine (GlcNAc) antibodies were prepared by affinity chromatography from serum of a healthy donor (MSS). They were heterogeneous but contained a unique antibody clonotype (1A) representing 7% of all anti-GlcNAc antibodies. Out of a series of monoclonal anti-idiotopic antibodies (anti-Id mAb), we identified five antibodies that bound to clonotype 1A as shown by isoelectric focusing and Western blotting. Two of them were specific for clonotype 1A (10F59 and 13F15), thus indicating its clonal origin. However, three anti-Id mAb (16F433, 16F539, and 16F812) bound to various additional portions of anti-GlcNAc antibodies of donor MSS. With the exception of one mAb, all anti-Id mAb have very similar relative affinities to clonotype 1A, so results from competition experiments between the different antibodies and between each antibody and antigen should reveal spatial relationships between the corresponding Id and between each Id and the antigen-combining site. The results show a consistent topography of Id on the V-region of clonotype 1A. Id 59, 812, and 433 were found to be arranged in one cluster (cluster I), whereas Id 15 and 539 belonged to a second cluster (cluster II). Cluster I resides completely in the antigen-combining site, whereas only Id 15 of cluster II weakly overlaps with the binding site. Our study demonstrates an analysis of spatial relationships of Id expressed on a human antibody clonotype. To our knowledge, this is the first demonstration of Id mapping on antibodies produced by a normal (nonmalignant) B cell clone that should be accessible to regulatory signals. Such analysis may contribute to a more detailed characterization of anti-Id mAb, and may provide additional information for a better understanding of their immunoregulatory effects.