Studies on alternaria allergens. II. Presence of two related antigens with contrasting allergenic properties in Alternaria tenius extracts.

Earlier, it was reported that most of the allergenic activity of Alternaria tenuis seemed to reside in the last Sephadex G-100 fraction (G3, molecular weight approximately 20,000). These conclusions were based on results obtained by the in vitro techniques of radioallergosorbent tests (RAST) and RAST inhibition. In the present studies, the allergenic activity of A. tenuis fractions was measured in vivo. It was found that fraction G3 was neither capable of inducing reaginic (IgE) antibodies in rats nor eliciting a skin reaction in rats sensitized with reagins against A. tenuis non-dialyzable fraction (MW greater than 12,000). On the other hand, subfractions G2D3 and G2D4 obtained from the middle fraction of G-100 (G2, MW approximately 30,000-40,000) followed by ion-exchange chromatography on DEAE-cellulose, showed the greatest allergenic activity in vivo, giving high titered reaginic antibodies in rats. When compared by RAST inhibition, the activities of fractions G2D3 and G2D4 were slightly lower than that of G3. Fraction G3 was immunogenic in rabbits. In immunodiffusion tests, G2D3, G2D4 and G3 appeared to be identical and they were cross-inhibiting in RAST inhibition tests. It was concluded that the sizes and multivalent properties of G2 and G3 antigens exerted a strong influence on their allergenic activities in rats (IgE antibody production) but this factor was of little importance for their antigenic activity in rabbits (precipitin antibody production) and their behaviour in the in vitro tests.