Selective isolation of allergens. I. Reaction of house dust mite extracts with tridacnin and concanavalin A and examination of the allergenicity of the isolated components.

Tridacnin, a lectin from the clam Tridacna maxima was found to precipitate with crude extracts from the house dust mites Dermatophagoides farinae and Dermatophagoides pteronyssinus. Using tridacnin in direct precipitation and affinity chromatography studies, a carbohydrate-rich preparation of high molecular weight was isolated from D. farinae extracts. The isolated preparation gave one precipitin line when used with tridacnin in gel diffusion and immunoelectrophoresis experiments but two bands were seen on polyacrylamide disc gels after electrophoresis at pH 8.9. Radioallergosorbent test (RAST) studies demonstrated that the isolated material reacted strongly with sera from human subjects allergic to house dust mites and accounted for a significant proportion of the IgE binding capacity of the crude D. farinae extracts. Only one out of fifteen mite-allergic subjects gave a positive response when prick tested with the isolated preparation at a concentration of 0.2 mg/ml. A possible explanation for the discrepancy observed between RAST and skin test results is discussed. Concanavalin A also precipitated with D. farinae extracts but the material isolated with this lectin did not react with tridacnin and reacted weakly in the RAST with sera from mite-allergic subjects. We suggest that the high molecular weight component(s) which react with tridacnin may be useful for immunotherapy of house dust mite allergy.