Background: Pollinosis, caused by grasses of the Poaceae family, is a problem worldwide. The relative importance of grass groups 1 and 5 major allergens is well established. However, not much is known about the recognition of these allergens by T cells and whether this T-cell reactivity correlates with skin reactivity and serum IgE levels.

Objectives: The aim of this study was to characterize the cross-reactive, grass allergen–specific T-cell responses from patients allergic to grass and nonatopic individuals and to investigate whether these responses correlate with grass-specific IgE and skin reactivity.

Methods: Skin prick test wheal areas and grass-specific serum IgE levels were determined in all patients (n = 21) and nonallergic control donors (n = 20). Peripheral blood mononuclear cells were isolated and stimulated with grass allergen extracts (Phleum pratense, Poa pratensis, Lolium perenne) and immunoaffinity-purified group 5 allergens, and the production of type 1 and type 2 cytokines was determined in the patient group.

Results: Donors allergic to grass showed increased T-cell–proliferative responses to grass allergens compared with nonatopic control subjects. We find it interesting that the magnitude of the patients' T-cell responses could not be correlated with the individual skin prick test areas and specific serum IgE levels, and several patients with allergies to grass had group 5–specific T-cell responses in the absence of group 5–specific IgE. The absence of a correlation between T-cell proliferation and IgE levels or skin prick test results may in part be explained by the finding that patients predominantly produced IL-5 in response to Phl p 5, the major allergen, and predominantly IFN-γ in response to Phl p extract. In general, all donors responded equally well to all three grasses. Additional experiments with Phl p 5–specific T-cell lines indicated that the equal proliferation of peripheral blood mononuclear cells to all three species is the direct result of cross-reactivity.

Conclusions: Grass allergen–specific T-cell responses are highly cross-reactive, and patients with allergies exhibit higher responses than nonallergic donors, suggesting that T cells are involved in the allergic reaction to grass group 5 allergens. However, group 5–specific T-cell responses are also found in donors without group 5–specific IgE, and the patients' grass-specific T-cell responses and cytokine production do not correlate to skin reactivity or to concentrations of grass-specific IgE. (J Allergy Clin Immunol 1998;101:241-9.)