The specificity of angiotensin-antisera. A cautionary note

Apparently monospecific antisera against the decapeptide angiotensin I (ANG-I) have been analyzed for their crossreactivity to the octapeptide angiotensin II (ANG-II). Whereas in the conventional displacement reaction of labeled ANG-I by ANG-II crossreactivities were in the order of 0.01%, the direct binding assay revealed crossreactivities of up to 20%. Both labeled ANG-I and ANG-II can be displaced completely from the antibody by an excess of either ANG-I or ANG-II. A similar relationship was seen with respect to the crossreactivity of ANG-II-antisera to ANG-I. - The data demonstrate that false positive immunocytochemical reactions may be obtained if the specificity of the reaction relies on the displacement reaction and the preabsorption of the antisera with the respective peptide. - These results may be pertinent for peptides other than the angiotensins.