Effects of immunization with LDH-X on fertility.

Immunological regulation of fertility can be best achieved if a defined macromolecule is used to provide the antigenic stimulus. Proteins with known enzymatic properties are attractive molecules in this area if it can be demonstrated unequivocally that they are unique constituents of spermatozoa, and are completely foreign to the female. This paper describes immunosuppression of fertility by the sperm-specific isozyme of lactate dehydrogenase (LDH-X). In addition, evidence is reviewed which suggests that acrosomal proteinase and hyaluronidase may be unique to sperm. Data are presented which confirm the sperm specificity of LDH-X and the immunochemical homogeneity of purified preparations of this isozyme. Immunization of female rabbits with LDH-X significantly reduces the fertility of these animals. Experimental results indicate that the primary effect of immunization involves blockage of fertilization. While those ova which are fertilized in an immune environment develop and implant normally, there is a high rate of post-implantation embryo mortality. Rabbit blastocysts transferred to immune recipients implant at the same rate as in non-immune controls. These findings are consistent with the conclusion that the developing embryo must interact with antibody during the pre-implantation stages of pregnancy when antigenic sites conferred by the sperm LDH-X are available. Such interaction can be demonstrated directly by immunofluorescence techniques.