New iew of cross-reactions in anti-angiotensin sera

Effects of different radioligands on the antigen binding specificity of somatostatin antisera

The regions of the somatostatin (SRIF) molecule recognized by five antisera were systematically studied using three radioligands (125I-N-Tyr-SRIF, [125I-Tyr1]-SRIF and [125I-Tyr11]- SRIF) and SRIF analogs containing sequential substitutions with alanine or tyrosine. Antisera SA and moreso SB had N-terminal specificity when used with [125 I-Tyr11]-SRIF but central molecular specificity when studied with the two N-terminal radiolabelled analogs. The N-terminal and central specific populations of antibodies in antiserum SB were separable by immunoaffinity adsorption using immobilized [Tyr1]-SRIF. It is of practical significance that the same antiserum (SB) could be used with different radioligands to perform N-terminal and central specific radioimmunoassays (RIAs). The central specific RIA detected SRIF-14 and SRIF-28 on an approximately equimolar basis whereas the N-terminal specific RIA was selective for SRIF-14.

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.