Parasite–specific T cell responses of sheep following live infection with the gastric nematode Haemonchus contortus

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Abstract
Summary Helper T cell lines recognizing antigen in the context of MHC Class II molecules were generated from peripheral blood mononuclear cells (PBMC) of sheep undergoing a primary or secondary infection with the nematode parasite Haemonchus contortus. The lines were used to identify 15–18, 25–29, 70–80 and > 100 kD immunodominant parasite larval antigens fractionated by SDS–PAGE under reducing conditions. Non–specific mitogenic activity in the antigen fractions was not detected. During primary infection PBMC did not respond to soluble antigens or those fractionated on SDS–PAGE, whereas T cell lines generated from these PBMC responded well. T cell lines and PBMC derived after a secondary infection responded similarly to fractionated larval antigen. This indicated that (a) the T cell lines had retained their antigen specificities (as represented by autologous PBMC reactivity) in spite of in–vitro cycles of restimulation with whole larval soluble antigen and subsequent expansion in recombinant human IL–2, and (b) proliferation of the antigen–specific PBMC was predominantly due to helper T cells. Variations between individual sheep in response to fractionated larval antigens was also observed. The pattern of helper T cell reactivity to SDS–PAGE larval antigens correlated poorly with B cell reactivity in the same animals by serum antibody Western blot analysis. These results demonstrate that helper T cell epitopes can be mapped in complex parasite antigen preparations in sheep and that this approach will be useful in the identification of parasite protective antigens in helminthiasis where the cellular or humoral nature of protection is not clearly defined.

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