Glycosylation may influence sex hormone-binding globulin measurements

A discordance between sex hormone-binding globulin (SHBG) measurements by 2-site ELISAs was investigated using pairings of various "in house" SHBG antibodies together with a concordant control. The 2-site monoclonal ELISAs used the same base coat (11F11) and discordance was observed with one top coat monoclonal antibody (7H9) and also when a polyclonal SHBG antibody was paired with the basecoat antibody (11F11). Sialidase treatment of the discordant sample and purified SHBG revealed increased levels using 7H9 whereas there was no change in SHBG in the concordant sample. Conversely, following sialidase treatment, the discordant sample showed no change in SHBG measured using the other monoclonal antibody pairings whereas the SHBG levels in the concordant sample declined following sialidase using the same monoclonal antibody pairings. This implicated glycosylation as a factor in antibody recognition and synthetic peptides spanning the two N-linked and one O-linked glycosylation regions showed that SHBG recognition by monoclonal antibody 7H9 could be disrupted by a peptide spanning the O-linked glycosylation site. Hence rather than immunoassay discordance being attributed to heterophile antibodies or other circulating antibodies here it can be likely attributed to glycosylation affecting antibody recognition and hence the measurement of SHBG.