IN-VITRO INHIBITION OF THE BIOLOGICAL-ACTIVITY OF FOLLICLE-STIMULATING-HORMONE BY ANTIPEPTIDE ANTISERA REPRESENTING THE HUMAN FOLLICLE-STIMULATING-HORMONE BETA-SUBUNIT SEQUENCE-33-53

There are few male contraceptive methods, and research is required to broaden the scope of available male antifertility methods, Two approac hes toward hormonal contraception are currently being investigated, Th e first relies on elimination of testosterone while the second is base d upon immunizations against FSH. However, most anti-whole FSH antiser a cross-react with LH, thereby possibly inhibiting testosterone and le ading to potential loss of libido, Therefore, a more effective alterna tive would be to define an FSH peptide that differs significantly from LH in order to prevent cross-reactivity between anti-FSH antisera and LH. Two peptides were selected from the beta subunit of FSH that were considered to be inducers of anti-FSH activity but not anti-LH activi ty. The first peptide (sequence beta 33-53) is a linear antigenic site of human FSH found only in anti-FSH antisera that do not cross-react with LH. The second peptide (sequence beta 81-95) is a part of FSH tha t confers receptor specificity. These peptides, in monomer and tandem form, were used to immunize rabbits. The antisera were tested for inhi bition of FSH activity in a bioassay; they were also tested in a Leydi g cell assay to detect anti-LH activity. It was found that antisera ra ised against the beta 33-53 tandem could inhibit the FSH bioactivity b ut not that of LH. Antisera against the beta 33-53 monomer or the beta 81-95 monomer or tandem did not inhibit FSH, Thus, the tandem peptide beta 33-53 is an attractive candidate for use as antigen in a male co ntraceptive vaccine, The better results obtained with tandem vaccinati ons might be related to the ability of the tandem peptide to direct th e antibody response toward the N-terminal end of the peptide and to ra ise antisera with the ability to react with shorter chains of amino ac ids.