Lethal recognition between Entamoeba histolytica and the host tissues.

Lethal recognition between Entamoeba histolytica and the tissues and defence systems of the host results in a continuous interplay that determines the development of pathological lesions: (i) we have identified several of the steps and mediators utilized by the trophozoites to destroy host cells by contact-mediated cytolysis; (ii) we have established that the alternative complement system represents the main defence available to the host against the invading parasite. The amoebae recognize target cells by means of a lectin specific for N-acetylgalactosamine-containing surface glycoproteins. This recognition appears to activate the amoeba to release, in the area of contact, an attack complex that induces the host cells to undergo cytolysis. The main component of the attack complex is thought to be amoebapore, an ion-channel forming protein that incorporates spontaneously into target cells leading to their depolarization by creating a pathway for ions to flow down their concentration gradient. The known properties of amoebapore are described. The acquisition of complement resistance by the invading trophozoites is essential for their survival within the host and therefore underlies virulence. The resistance to complement killing is not a permanent property of the amoebae. It is lost during axenization and reappears on passage through the host or when the trophozoites are grown axenically in the presence of active complement.