Effects of parasitism on cellular immune response in sheep experimentally infected with Haemonchus contortus

This work aimed to study the possible relationships among the magnitude of abomasal worm burden and the proliferation of globular leucocytes and mucosal mast cells in the abomasal mucosa, and the white blood cell count. Eighteen Suffolk × Greyface lambs were infected with Haemonchus contortus, and 12 were kept free of nematodes. Blood samples were collected on days 0, 30, and 57 post-infection (p.i.) for leucogram determination. At day 62, all animals were euthanized to count the total number of nematodes recovered in the abomasum and to count the number of mucosal mast cells and globular leucocytes. On day 57, higher levels of parasitism corresponded to lower leucocyte counts. The infected groups had lower lymphocyte counts throughout the experimental period. Animals with higher numbers of parasites had lower neutrophil and eosinophil counts on day 57. The lower the worm burden, the greater the number of mucosal mast cells (r = −0.85; p < 0.01) and globular leucocytes (r = −0.87, p < 0.01) observed. The sheep most resistant to haemochosis had greater peripheral and tissue cellular immune responses.