Monoclonal antibodies to testosterone: the effect of immunogen structure on specificity

A 15 beta-thioalkyl derivative of testosterone conjugated to bovine serum albumin (BSA) was synthesised and used to produce monoclonal antibodies. These antibodies were evaluated using 15 beta-(2-carboxyphenylthio)-testosterone [125I]histamine as radioligand. Out of 1368 hybrids, 5 secreted anti-testosterone antibodies. These were compared with monoclonal antibodies derived from immunisation with testosterone-3-carboxymethyloxime-BSA. The first group of monoclonal antibodies all showed very low cross-reactivity with 5 alpha-dihydrotestosterone (less than 2.8%) indicating that this site of linkage is a good choice for discriminating between differences at the 4-5 position in the A-ring on the testosterone molecule. However they generally showed much higher cross-reactivity with progesterone and androstenedione than monoclonal antibodies raised to the 3-linked immunogen. Nevertheless within each fusion there were monoclonal antibodies with markedly different specificities. None of these antibodies could be considered suitable for use in a testosterone immunoassay, but it does suggest that an antibody with an improved specificity profile could be found using the monoclonal antibody approach.