Monoclonal antibodies to pig angiotensinogen recognize minor idiotypes

We have produced monoclonal antibodies to a highly purified pig (P) angiotensinogen preparation and characterized their ability to bind [125]I-P- angiotensinogen. Lymphocytes of RBF/Dn mice immunized with P-angiotensinogen were fused with FOX-NY myeloma cells and clones were isolated by binding to [125]I-P-angiotensinogen and by an immunodot blot assay. Three of 16 clones which recognized P-angiotensinogen were characterized. Isolated monoclonal antibodies bound only 10-15% of the total [125]I-P-angiotensinogen; however, the bound counts could be displaced with unlabelled P-angiotensinogen. None of the monoclonals inhibited the cleavage of P-angiotensinogen by homologous renin, nor did they bind to the NH-terminal angiotensin I (ANG I) peptide. Little or no binding was detected to angiotensinogens in human, monkey, rat, rabbit, sheep or bovine serum. Mixtures of the clones and analysis of the immune complexes by PAGE indicated that different binding sites on different P-angiotensinogen were detected by some of the monoclonals, while the same or competing sites were recognized by others. No combination of clones tested significantly increased the amount of P-angiotensinogen bound. We interpret these findings to indicate that monoclonal antibodies to 'purified' pig P-angiotensinogen recognize species-specific minor epitope subsets of the protein, but not antigenic determinants common to all.