Antisperm antibodies (ASAs) are proteins made by the body’s immune system that can attack sperm. When ASAs attack sperm, they damage the sperm and limit their motility causing what is called “immune infertility.” Based on current data, ASAs are not believed to be common. However, poor testing standardization and a lack of data on their presence in the general healthy population limit current scientific knowledge.

ASAs can be made by both people with male sex organs and people with female sex organs. In people with male sex organs (a prostate), sperm are made in the testis (testicles) and are protected from the immune system by something called the blood-testis barrier. ASAs can develop if there is damage to this blood-testis barrier because the body’s immune cells get exposed to sperm and see them as foreign. As a result, the body can start attacking the sperm and cause infertility problems.

Damage to the blood-testis barrier can happen due to a range of reasons, such as: 
1. A semen infection
2. A surgical procedure (e.g., vasectomy)
3. A testicular injury
4. Other causes

Overall, this type of infertility has a relatively low prevalence in people with a prostate, impacting about 2.6 - 6.6% of infertile people in this population. Research also shows that ASAs appear to be more common among people with a prostate of reproductive age who have what is known as “idiopathic fertility,” meaning that they are infertile for an unexplained reason. Among this group, about 18% are shown to have ASAs. More research is needed to make sure that these estimates are accurate and to explain why ASAs develop. Some research is underway to help us answer these questions. 

In one small study, for instance, ASAs were found in 10% of men who had receptive anal sex with men. Some researchers have also suggested based on data that ASAs may be more likely to occur in men who have oral sex with men. These findings help show us how common ASAs might be and what factor might put someone at higher risk of developing ASAs. Much more research is needed to help us understand the prevalence of ASAs and risk factors for ASAs. Other possible causes of ASAs in people with a prostate are thought to be smoking and past history of a sexually transmitted disease.

In people with female sex organs (individuals who have a cervix), we know based on research that the presence of ASAs is also likely not common, and also that ASAs appear to be more common in people with a cervix who have unexplained infertility. One small study found that about 18% of women who were infertile had ASAs. Research is still being carried out to understand why ASAs develop in people with a cervix.
We know, for instance, that ASAs do not develop in the vagina or reproductive tract following exposure to sperm during sex.

The absence or presence of ASAs is also not related to previous sexual activity. This means that ASAs can not indicate whether or not someone has had sexx before. ASAs in people with a cervix may result from genital or gynecological infections, trauma or injury to the vaginal mucosa, or anal or oral sex wherein sperm enter the digestive tract. 

ASA testing is usually only performed during an evaluation for a person or a couple with unexplained infertility. However, ASAs are not mentioned by the World Health Organization as a significant cause of infertility and not all experts believe that ASA testing is helpful. Body fluids, including semen and sperm analysis, may be conducted in people with a prostate. In people with a cervix, a test called a sperm immobilization test can be carried out with a blood sample, or a doctor can test a person’s cervical mucus for ASAs.

Treatment for ASAs to support pregnancy may include immunosuppressive therapies or assistive reproductive therapies (e.g., sperm washing followed by artificial insemination or in vitro fertilization).

Antibodies, or immunoglobulins, are an important part of the immune system. These proteins help the body fight germs and foreign invaders, including viruses, bacteria, allergens, and fungi. Antibodies attack the foreign substance, neutralize it (or make it less harmful), and get it out of the body. Sometimes the body develops antibodies to its own tissue as is the case in autoimmune conditions, including type 1 diabetes and multiple sclerosis.

There are five types of antibodies that are abbreviated using “Ig” and an additional letter based on where the antibody is found. The “Ig” stands for immunoglobulin. 

1. IgA is found in saliva, tears, mucus, breastmilk, and intestinal fluid. It protects the body against substances that are inhaled or ingested.
2. IgD is found on the surface of B cells (a type of special white blood cell). Its role is not entirely known, but it is thought to support B cells, including how they mature and function.
3. IgE is found in the skin, lungs, and mucus membranes. It helps to fight allergic reactions by causing the body to release histamine and other substances into your bloodstream.
4. IgG is the most common antibody in the body and is found in blood and tissue fluids. It helps protect the body from viruses and bacteria.
5. IgM is found in the blood and lymph systems. It plays a large role in immune regulation and is usually the first defense against infection.

Antisperm antibodies (ASAs) usually belong to two different immunoglobulin groups (IgA and IgG).