Structure and activity of ragweed antigen E: II. Allergenic crossreactivity of the subunits

Abstract

Recently we have reported the isolation of the two subunits (α and β) of ragweed antigen E (AgE) in their active form. In the present work we have compared the allergenic activity of the two subunits with native AgE by the radioallergosorbent test (RAST) and by inhibition of the RAST. Also, the amounts of IgE antibodies in 30 ragweed-sensitive sera bound to α and β subunits as well as native AgE were measured by RAST. In all individuals the percentage of RAST binding was greatest to native AgE; however, varying patterns of reactivity to α and β subunits were noted. In RAST inhibition experiments, free β subunit was equally effective in inhibiting the binding of IgE antibody (from a pooled ragweed-sensitive sera) to immobilized α or β subunit. Similarly, fluid-phase α subunit inhibited in a comparable manner the binding of IgE antibody to solid-phase α or β subunits. In further RAST inhibition experiments 7 × 10 −13 moles of fluid-phase native AgE was required for 50% inhibition of the binding of IgE antibody to solid-phase native AgE. Larger molar amounts of fluid phase β (3.5 x 10 −11) and α (3 × 10 −10) were needed for 50% inhibition of the binding of IgE antibody to solid-phase native AgE. AgE allergenicity as measured by RAST could not be totally reconstituted by recombination of equimolar quantities of α and β subunits. Less than 1 × 10 −12 moles of fluid-phase native AgE inhibited the binding of IgE antibody to solid-phase α or β, greater than 50%. Finally, the isolated chains are biologically active as demonstrated by their ability to provoke wheal-and-flare skin reactions in subjects allergic to ragweed pollen, and the activities of the chains were approximately equivalent on a weight basis to native AgE.