One lump or two?

Sperm clue to 'disease immunity'
The female reproductive tract is a "hostile environment" for foreign cells which are readily attacked by the immune system but sperm move through apparently undetected. Sperm are also protected from harm in the testes from the male's own immune system. The Imperial College team says it has found specific sugar molecules on the surface of sperm which seem to be responsible for evading the immune response.