RADIOIMMUNOASSAY FOR PBTX-2-TYPE BREVETOXINS - EPITOPE SPECIFICITY OF2 ANTI-PBTX SERA

Antiserum against PbTx-2-type brevetoxins was produced by immunizing r abbits with a PbTx-2-bovine serum albumin (BSA) conjugate, This serum had a higher affinity, but lower titer, than our current goat serum, U sing 4 natural brevetoxins and 6 synthetic derivatives as competitors in our brevetoxin radioimmunoassay, we determined the epitope specific ity of both sera. Modification of the backbone structure at C-42 on th e K-ring had little or no effect on the antigen-binding capability of either serum, Reduction of the double bond between C-2 and C-3 on the A-ring by reduction of the lactone decreased binding 500 to 750-fold. Epoxidation of the double bond between C-27 and C-28 on the H-ring did not affect binding, which suggested that the goat serum is specific f or the A-ring region of the brevetoxin backbone, In contrast, modifyin g the A-ring had no effect on rabbit serum binding. However, epoxidati on of the H-ring decreased binding 5 to 20-fold, which suggested that the rabbit antiserum is specific for the H-ring region of the molecule , These results suggest that assays utilizing only one antibody may no t adequately detect toxin metabolites if molecules are altered in the critical region of antibody recognition.