title: Immunological responses of sheep to Haemonchus contortus.
abstract: Infections with Haemonchus contortus are a major constraint on ruminant health world-wide. Young lambs are very sensitive to Haemonchus infection. Older lambs and sheep acquire immunity after a continuous or seasonal exposure to the parasite. The mechanisms underlying immunity are still not completely understood. Antibodies, in particular local IgA and IgE, certainly play a role. The role of IgG is less clear. Lymphocyte proliferation responses seem to correlate to immunity. Sheep that have high antigen-induced lymphocyte responses have a low susceptibility to infection. Furthermore, several studies have demonstrated that immunity against H. contortus is associated with mastocytosis and hyper-sensitivity reactions. More recently, increasing attention is being paid to the role of cytokines (interleukins and gamma-interferon) in the activation of specific defence mechanisms. Reverse transcriptase-polymerase chain reaction (RT-PCR) assays to study cytokine mRNA expression have become available. The inability of young lambs to mount a significant Th2 response, which is normally characterized by high IgE levels, mastocytosis and eosinophilia, may account for the phenomenon of unresponsiveness in these animals.
authors.affiliation: rita.henk@consunet.nl
authors.forename: H D
authors.initials: HD
authors.lastname: Schallig
mesh_terms: D000375:Aging / Q000276:immunology; D000818:Animals; D004804:Eosinophils / Q000276:immunology; D006188:Haemonchiasis / Q000276:immunology*; D006189:Haemonchus / Q000276:immunology*; D007070:Immunoglobulin A / Q000276:immunology; D007073:Immunoglobulin E / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology; D008213:Lymphocyte Activation; D008407:Mast Cells / Q000276:immunology; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology*
chemical_list: D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007073:Immunoglobulin E