Induction of T helper 1-and T helper 2-type immune responses during Haemonchus contortus infection in sheep

The production of cytokines by lymphoid cells, isolated from non-infected a nd Haemonchus contortus-infected lambs, was investigated. Particular attent ion was paid to differences in T helper 1-(Th1) and Th2-type immune profile s between genetically resistant and random-bred animal groups. Non-infected resistant and random-bred lambs produced equivalent levels of interferon-g amma (IFN-gamma) and interleukin-5 (IL-5), from isolated abomasal lymph nod e cells (ALN), mesenteric lymph node cells (MLN) and spleen cells (SC), in response to in vitro stimulation with T-cell mitogen (concanavalin A) or la rval parasite antigen. ALN and MLN cells derived from infected resistant an d random-bred lambs produced relatively lower levels of IFN-gamma, followin g in vitro stimulation with parasite antigen, when compared with their unin fected counterparts. In contrast, infected lambs of both groups showed enha nced mitogen- and antigen-stimulated production of IL-5, in comparison with uninfected controls, at days 5 and 28 postinfection (p.i.). Mitogen- and a ntigen-stimulated IL-5 responses were higher among resistant lambs compared with random-bred lambs, with the highest overall production of IL-5 by par asite antigen-stimulated ALN and MLN cells. Among day 28 p.i. lambs, levels of cell culture-derived parasite-specific immunoglobulin G1 (IgG1) and IgE antibodies were higher in resistant lambs than in random-bred lambs, follo wing in vitro stimulation of SC or ALN cells with parasite antigen. Finally , after 28 days p.i., histological examination of abomasal tissue revealed higher densities of mast cells and eosinophils in the mucosa of resistant l ambs than in random-bred lambs. Taken together, these data support the noti on of a strong Th2-type immune response to Haemonchus infection in genetica lly resistant sheep, and support the claim for a Th1/Th2 dichotomy in rumin ants.