The high idiotypic connectivity of "natural" newborn antibodies is not found in adult mitogen-reactive B cell repertoires.

Unselected IgM-secreting hybridoma collections were established either from unprimed naturally activated newborn spleen cells or from mitogen-stimulated adult B cells. These were then screened for reactivity with a panel of monoclonal anti-idiotypic antibodies and haptens. While the finding of hapten-specific antibodies was equally frequent in either collection, newborn antibodies reacted at least 10 times more frequently with the anti-idiotypic reagents. The reactivity patterns of individual antibodies readily demonstrated the overall specificity of these V-region interactions. Since some of the idiotopes screened are characteristically not expressed in immune responses by the strains analyzed, and are in fact not expressed in the adult induced hybridoma collection, we explain these findings by a unique property of the set of natural (newborn) antibodies i.e. the high levels of idiotypic connectivity previously described within this repertoire.