The immune response to hCG-beta subunit in rats and the effects of active immunisation on their fertility

Immunogenicity of hCG beta subunit (beta-hCG) was investigated in female rats using a variety of immunisation schedules and the effects of active immunisation on fertility were studied. Antibody production to beta-hCG conjugated to tetanus toxoid was pronounced and was not enhanced by the use of adjuvants or presensitisation to tetanus toxoid carrier. Nor was it diminished by using half the amount of beta-hCG-TT conjugate. Boosting resulted in a marked secondary response producing high titre antibody over a prolonged period. Partial or complete infertility occurred in the beta-hCG immunised rats, dependent on which immunisation schedule was employed, implying a threshold titre of antibody required to interfere with pregnancy. No significant effect was observed on the oestrous cycle of the immunised rats or on the gross morphology of their progeny. The results are discussed in relation to the hormonal control of reproductive function in the rat, and the possible application of immunisation against beta-hCG to human fertiliyt.