Schistosoma mansoni: the egg, biosynthesis of the shell and interaction with the host.

The schistosome eggshell is a hardened and tanned structure made from cross-linked proteins. It is synthesized within the female worm from many different kinds of proteins and glycoproteins. Once the egg is released in the circulation, the outer surface of the eggshell is exposed and hence a direct site of interaction between the parasite and the host. The major eggshell protein is p14, but about one third of the eggshell is made from common cellular proteins, some of which are known to be immunogenic. This has many consequences for parasite-host interactions. However, so far, the eggshell has gained little attention from researchers. We will discuss the structure of the eggshell and its role in granuloma formation, host factor binding and egg excretion.