؉ EM T cells, as well as that of cells simultaneously producing both IL-17A and TNF-␣, to be significantly elevated in the Giardia-exposed individuals after 24 h of antigen stimulation. In supernatants of PBMCs stimulated with Giardia antigens for 6 days, we found inflammation-associated cytokines, including 1L-17A, as well as CD4 ؉ T cell activation and proliferation, to be significantly elevated in the Giardia-exposed individuals. We conclude that symptomatic Giardia infection in humans induces a CD4 ؉ EM T cell response of which IL-17A production seems to be an important component.