Analysis of human choriogonadotropin core 2 o-glycan isoforms

Measurements of human choriogonadotropin (hCG) isoforms containing core 2 o-glycans may be useful for diagnosis of Down Syndrome pregnancies and trophoblastic disease. As shown here, this isoform is also present in pituitary extracts, early pregnancy urine, and urine of postmenopausal women. Although, measurements of hCG isoforms may be useful in several clinical settings, this remains to be determined due to the lack of suitable standards and the difficulties of comparing data obtained in different laboratories. Here, we report that monoclonal antibodies B152 and CTP104 recognize the third (Ser132) and fourth (Ser138) o-glycans, respectively, in the carboxyterminal portion of the hCG beta-subunit. The proximity of these sites prevents B152 and CTP104 from binding simultaneously to isoforms containing core 2 o-glycans. Unlike B152, which binds only the core 2 isoform, CTP104 recognizes both glycan moieties. By measuring hCG with CTP104 in the presence and absence of B152, one can quantify both isoforms using the same readily available standard.