A Yale-led research team has uncovered how a naturally occurring biological mechanism is able to prevent sperm cells from interacting with an egg, preventing fertilization. In the United States, 9% of men and 11% of women of reproductive age experience fertility problems. Some of these problems stem from failures in the proper recognition, adhesion, and fusion of sperm and an egg. The IZUMO1-JUNO connection enables sperm and egg recognition and fusion. This naturally occurring antibody was discovered 40 years ago at Osaka University in Japan, and it can recognize IZUMO1 and disrupt fertilization.