Parietaria profilin shows only limited cross-reactivity with birch and grass profilins

Background: In patients showing multiple reactivity to seasonal airborne allergens, a skin prick test (SPT) with Parietaria pollen scores frequently negative, suggesting that profilin from Parietaria might not share IgE-binding epitopes with profilin from botanically unrelated airborne allergens. This study investigated the immunologic cross-reactivity between profilins from Parietaria, grass and birch pollen.

Methods: 36 patients hypersensitive to birch profilin, Bet v 2, underwent SPT with Parietaria, and IgE to both whole Parietaria pollen and Phleum profilin were sought in their sera by ELISA. In ELISA inhibition studies, IgE reactivity to Phleum profilin was measured before and after absorption of sera from Parietaria reactors with both whole Parietaria pollen extract, and Par j 1/Par j 2 fraction. Further, their IgE reactivity to whole Parietaria pollen was measured before and after absorption with the Par j 1/Par j 2 fraction.

Results: All sera showed IgE reactivity to Phleum profilin. Only 14/36 (39%) patients had a positive SPT to Parietaria and 17/36 (47%) showed IgE to Parietaria. Absorption of sera from Parietaria reactors with whole Parietaria extract caused a marked reduction in IgE reactivity to grass profilin; in contrast, absorption of sera with the Par j 1/Par j 2 fraction did not exert any inhibitory effect on IgE reactivity to grass profilin. Absorption of sera with the Par j 1/Par j 2 fraction markedly reduced IgE reactivity to whole Parietaria extract in 8/9 cases.

Conclusion: Less than 50% of patients sensitized to birch and grass profilin cross-react to Parietaria profilin. In most cases, cross-reactors are hypersensitive to major, specific Parietaria allergens as well. This findings may be of practical relevance when the prescription of specific immunotherapy is considered.