Sperm's Anti-Germ 'Shield' Might Play Role in Fertility

Preliminary new research points to the possibility that some infertile men could benefit from boosting a protein shield that protects sperm cells from germs.

While it's too early to know if the research will lead to any new treatments, one infertility expert said that any treatment would most likely be applied only to sperm used in the process of in-vitro fertilization.

Still, the expert, Gary Cherr of the University of California, Davis, noted that "this study adds another piece to the puzzle" surrounding men who are infertile for no apparent reason because it suggests something may be wrong with the germ-fighting sperm shield.

At issue in the new study are proteins known as defensins, which provide protection against germs. In particular, the researchers looked at one protein known as human beta-defensin 1, which is found in a variety of types of tissue in the body, "but its role in the male reproductive tract is not clear," said study co-author Hsiao Chang Chan, a professor at the school of biomedical sciences at the Chinese University of Hong Kong.

Other research has suggested that men may become less fertile if these proteins are missing. Cherr noted, "Sperm would need antimicrobial protection from microbes that are present in the female reproductive tract."

This fact raises the possibility that boosting the levels of the proteins would provide more protection against germs as sperm try to survive long enough to fertilize a female egg.

The new study tested this idea in the laboratory.

The researchers checked the levels of human beta-defensin 1 in the sperm cells of men who suffered from poor sperm motility (asthenozoospermia), meaning that their sperm don't move properly, or a fairly common infection within the genital tract known as leukocytospermia. The investigators found that the protein levels were lower than in men without fertility problems.

The researchers also boosted the levels of the protein in the sperm cells and found they moved more efficiently, had greater germ-fighting powers and could penetrate eggs more effectively.

Chan said the researchers included the sperm of 325 infertile men and 190 fertile men.

The next steps are to continue research and understand whether boosting the levels of the protein is safe, Chan noted.

Other questions remain as well.

Cherr, who studies infertility and is a professor of environmental toxicology and nutrition at UC Davis, said it's not clear why boosting human beta-defensin 1 on sperm would have an effect on fertility since the protein is found in the female reproductive tract also and would presumably fight germs there.

An estimated 10 percent to 15 percent of couples are infertile, the study authors noted. According to the American Society for Reproductive Medicine, men are fully or partially responsible for infertility in 40 percent of couples who are unable to conceive.

The study is published in the Aug. 13 issue of Science Translational Medicine.

More information

For more about infertility, visit the U.S. Centers for Disease Control and Prevention.