Immune mechanisms in trematode-snail interactions.

Digenetic trematodes, including several species of medical and veterinary significance, nearly all depend on molluscs (usually gastropods) as hosts for asexual reproduction. The molluscan internal defence system, although lacking many of the familiar features of the vertebrate immune system, may pose a substantial obstacle to digenean development. In this article, Wil van der Knaap and Eric Loker discuss the manner in which this system is mobilized to kill larval trematodes and the real and putative mechanisms of digenean evasion of molluscan immune responses. These two possible outcomes of trematode-snail associations make them intriguing model systems for exploring processes of parasite infectivity and host resistance.