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Abstract
Antibodies against a particular antigen are mainly obtained by direct injection of an antigen or antigen-carrier complex into a suitable host. An alternative method is based on the idiotypic network theory and requires the injection of a primary antibody into a syngeneic animal. These antibody-induced immunoglobulins exhibit similar binding characteristics towards the antigen than the primary antibody.
During this investigation we analyzed a panel of antibody-induced antibodies against the heavy metal Pb. The analysis of the genes utilized to assemble these immunoglobulins revealed a limited gene usage at the heavy chain locus, and the dominance of one particular light chain gene family. The heavy chain variable regions are dominated by genes of the $\rm V\sb{H}J558$ origin with high sequence homology, while the majority of light chain genes belong to the $\rm V\sb\kappa20$ family. Southern blot analysis showed that this restriction is due to selection rather than a clonal relationship. This points towards an 'oligoclonal' immune response.
The possible alteration of cellular regulatory mechanisms resulting in a break down of 'allelic exclusion' was studied on the nucleotide and protein level. Although two functionally rearranged transcripts were found within the same cell, only one transcript resulted in the secretion of a full length immunoglobulin molecule.
The light chain sequences belonging to the V$\kappa$20 family were analyzed for a possible Pb binding site using molecular modeling technique. Based on the model site directed mutagenesis was performed to alter possible key residues, and an in vitro expression system was developed that allows further studies of the binding characteristics with expressed and purified antibodies.
Finally, molecular modeling techniques and electrostatic potential calculations were utilized to analyze several representative antibodies for possible Pb binding sites
