Men can make antibodies to their own sperm when something has happened to break down the immune barrier which exists between the testicles and the blood. If you think about it, all sperm are different and the miracle is that every man does not produce antibodies to what are not his usual cells. Infection, surgery and injury can all lead to the formation of antibodies, but in most cases there seems to be no reason for them.
If the antibody concentration is high, fertility can be quite severely reduced as the sperm find it difficult to fertilise an egg when they are attached to antibody molecules. The only good way of treating such couples is by a process known as ICSI (intracytoplasmic sperm injection), which means taking a single sperm and injecting it into a single egg during an IVF cycle. This is dramatic stuff but the success rates are nearly as high as straightforward IVF, that is, about one chance in three of pregnancy.