The immune response and the evaluation of acquired immunity against gastrointestinal nematodes in cattle: a review

The present review discusses the immune responses to gastrointestinal nemat odes in cattle and the different immunological and parasitological paramete rs used to assess acquired immunity. Measuring acquired immunity to gastroi ntestinal nematodes in cattle (e.g. for the evaluation of candidate parasit e vaccines) is hampered by the limited understanding of bovine immune respo nses against gastrointestinal parasites. In this paper the available data o n protective immunity against gastrointestinal nematodes, and especially Os tertagia ostertagi, in cattle are compared with the current knowledge of pr otective immune responses against gastrointestinal nematodes in rodent mode ls and small ruminants. In contrast to the immune response in mice, which i s controlled by T helper 2 (Th-2) lymphocytes and results in mast cell- or goblet cell-mediated expulsion of adult worms, bovine immune responses to O . ostertagi do not show a clear Th, cytokine profile, nor do they result in rapid expulsion of the parasite. The first manifestation of immunity to O. ostertagi in calves is a reduction of worm fecundity, possibly regulated b y the local IgA response; Worm numbers are only reduced after a prolonged p eriod of host-parasite contact, and there are indications that O. ostertagi actively suppresses the host's immune response. Until the mechanisms of pr otective immunity against O. ostertagi are revealed, the use of immunologic al parameters to estimate acquired immunity in cattle is based on their cor relation with parasitological parameters and on extrapolation from rodent a nd small ruminant models. Assessing the resistance of calves against a chal lenge infection by means of parasitological parameters is probably still th e most accurate way to measure acquired immunity against gastrointestinal n ematodes.