Immunological distinction of ovine follitropin agonist and antagonist.

The presence of antennary carbohydrate structure(s) in ovine follitropin is required for full biologic activity. In order to explore the biochemical basis for the conversion of the glycosylated agonist form of the hormone into one that is antagonistic in nature when it is deglycosylated, we have produced antisera in rabbits to these preparations. All antisera produced in rabbits against deglycosylated ovine follitropin (DG-oFSH) (antagonist) contained antibodies that were specific to the deglycosylated hormones with the native hormones showing weak and non-parallel cross-reaction (less than 10%) but with rabbit antibodies to the native hormone the DG hormone, which is an antagonist, was fully reactive. Using oFSH, asialo-FSH (A-FSH), and DG-oFSH we have shown that removal of sugars internal to sialic acid is required to produce these specific antibodies. This is in complete agreement with the observation that extensive deglycosylation of these hormones is necessary to induce changes in biological activity at the cellular level. By affinity chromatography on divinylsulfonyl Sepharose immobilized oFSH, antibodies that recognize both agonist/antagonist could be separated from immunoglobulins that preferentially bound the labeled antagonist. Based on these data, we suggest that chemical deglycosylation may result in changes in antigenic structure of follitropin by generation of new determinants and thus specific antibodies become available for distinguishing the agonistic and antagonistic forms of the hormone.