Assaying glycoprotein hormones--the influence of glycosylation on immunoreactivity

The epitopes of the human glycoprotein hormones (follicle-stimulating hormone [hFSH], luteinizing hormone [hLH], chorionic gonadotrophin [hCG], thyroid-stimulating hormone [hTSH] and erythropoietin [hEPO]) appear to consist only of peptide components. Their interactions with antibodies, however, are influenced by their bulky and often highly charged carbohydrate moieties. Thus, isoforms of these hormones (the majority of which are glycoforms) differ in their specific immunoreactivities as well as in their specific in vivo and in vitro bioactivities. This can create difficulties for the standardization of immunoassays as the isoform composition of a hormone depends both on its source and method of isolation.