Specificity of antibodies to ovarian hormones in relation to the site of attachment of the steroid hapten to the peptide carrier

Article abstract of DOI:10.1016/0039-128X(72)90076-1

Estradiol-17β, estriol and progesterone were rendered antigenic by covalent attachment to bovine serum albumin through ring B or C of the steroid molecule. Coupling to lysine residues of the protein was effected via the 6-(O-carboxymethyl)-oximes of the estrogens and via the 6-(carboxymethylene) thioether or the 11α-hemisuccinate of progesterone, by use of the carbodiimide reagent. Antisera to the estradiol 6-conjugate raised in rabbits or goats distinguished estradiol-17β more efficiently from estrone, estradiol-17α and estriol than did antisera to estradiol-17β-hemisuccinate-BSA; neither serum reacted with non-phenolic steroids or non-steroidal estrogens. Antisera to estriol 6-conjugates showed minimal cross-reaction with estradiol-17β and estrone. Rabbit antisera against the progesterone 6-conjugate did not react with phenolic or C₁₉-steroids, cr with corticosterone, and only feebly with 11-deoxycorticosterone and 20α-or 20β-dihydroprogesterone; significant crossreaction occurred with 17β-hydroxyprogesterone and 3β,17α-dihydroxypregn-5-en-20-one (3-4%), Δ⁵-pregnenolone (8-14%) and with 5β- and 5β-dihydro-progesterone (100%). Sera against the 11-conjugate were better able to recognize changes about the A-ring and failed to cross-react with 5α-dihydroprogesterone (< 3%). Both sera showed greater specificity than reported for antibodies to 20-conjugates of progesterone towards the D-ring and 17-sidechain and were similar in this respect to antibodies elicited by 3-conjugates described in the literature. It is concluded that the site of attachment of steroid haptens to the peptide carrier importantly affects the specificity of the antibodies produced.