Würtzen PA, et al. - Given that allergic symptoms are induced by various related ragweed species with diverse geographical distribution in the US, and cross-reactivity towards related ragweed species of IgE and treatment-induced IgG4 has been shown earlier, researchers intended to gain information regarding the underlying T-cell cross-reactivity. Participants were 20 American ragweed allergic patients, and an additional 11 American and 14 Slovakian ragweed allergic donors. The implication of T-cell epitopes of multiple allergens/isoallergens in the diverse T-cell responses in ragweed allergic subjects was revealed in this study. Without any apparent geographical response bias, they found high cross-reactivity of T-cell lines to epitopes of related ragweed species. Findings lend support to the idea that different ragweed species can be thought of as an allergen homology group with Amb a as the representative species about the diagnosis and allergy immunotherapy.