Genetic and other constraints on resistance to infection with gastrointestinal nematodes.

Infections with gastrointestinal (GI) nematodes are among the most prevalent infections of man. Not only are they common and widespread in populations throughout the world, but they are frequently chronic and occur repeatedly throughout the lifetime of an individual. It is now well established that such parasites can be highly immunogenic and that their environment, the gastrointestinal tract, is well equipped to mount potent immune and inflammatory responses. The abundance and long-term survival of GI nematodes therefore present a paradox. This review takes the standpoint that man as a species has the capacity to produce effective and protective responses against GI infections, but that this capacity is subject to a number of powerful constraints, arising from parasite evasion, depression of response capacity and deficiency in response capacity. These constraints are discussed in the light of evidence drawn from experimental studies with animal models.