The test for anti-sperm antibodies in sperm is performed to detect possible causes of male infertility.
Screening for anti-sperm antibodies is one of the tests used to investigate male infertility and detects specific antibodies in sperm. The presence of antibodies in sperm can lead to reduced fertility. Infertility due to immunological causes (immune infertility) makes up a significant proportion of infertility cases of unknown etiology. Class anti-sperm antibodies may be IgG or IgA and the binding site may be in the head, neck, and tail of the spermatozoon. Binding of more than 50% is usually associated with a significant decrease in patient's fertility.
IgA class anti-sperm antibodies, which are usually binding to the sperm tail, are associated with poor motility and poor sperm penetration into the cervical mucus.
IgG class anti-sperm antibodies, commonly binding to the head of spermatozoa are associated with inhibition of sperm-egg fusion.
Screening for the presence of anti-sperm antibodies is indicated not only for the investigation of male infertility but also when sperm agglutinations are observed during the sperm analysis or when macroscopically visible (macro) agglutinates are present. It is also used in men with a history of testicular injury, biopsy, surgery (such as sperm duct anastomosis), genital infections, or ejaculatory duct obstructions.
How are anti-sperm antibodies formed?
Human blood and sperm do not come into contact with each other because of a barrier system (blood-testis barrier) in the testes. Specialized cells known as Sertoli cells are involved in this system (a similar barrier system exists in the brain called the blood-brain barrier). Any disorder of this system as a result of physical or chemical causes, infections, inflammation or injuries, can disrupt the blood-testis barrier and sensitize the immune system to sperm components. Sometimes infections or inflammation in other parts of the genital system can lead to the production of these antibodies.
Why do anti-sperm antibodies intervene in fertilization?
Anti-sperm antibodies bind to proteins (antigens) in either the sperm head, neck, or tail. Anti-sperm antibodies can disrupt sperm function in three ways:
- Agglutinations of spermatozoa (adhesion and agglutination), resulting in a decrease in the number of sperm that penetrate the cervical mucus
- Immobilization of spermatozoa, so they cannot move
- Sperm toxicity, thereby reducing the viability of the spermatozoa
Antibodies can also influence the penetration of the sperm into the oocyte and sometimes prevent the sperm from moving through the cervix. It is extremely unlikely to achieve normal pregnancy even with intrauterine insemination, in the presence of anti-sperm antibodies. In order for fertilization to occur, the sperm head must first be attached to the zona pellucida of the egg. Anti-sperm antibodies also interfere with this binding.
In some patients, anti-sperm antibodies may be found in the blood. These are called serum anti-sperm antibodies. Serum anti-sperm antibodies are often found in men suffering from testicular obstruction (a common cause of low sperm count or poor motility) and in 30-70% of men who have undergone sperm duct ligation. Re-absorption of sperm from the excluded ducts results in the formation of sperm autoantibodies due to the interaction of spermatic antigens with the immune system.