Journal of Immunological Methods, 61 (1983) 335-338 335 Elsevier A Rabbit Antibody Inhibition Test to Detect the Antigenic Activity of Allergen Extracts L. Di Berardino 1:, O. Brenna 2 and S. Centanni 3 I Lofarma Allergeni, Research Laboratory, Milan, 2 Department of Organic Chemistry, University of Milan, Milan, and 3 11 Clinic of Respiratory Diseases, University of Milan, Milan, Italy (Received 10 September 1982, accepted 29 january 1983) A method for standardizing the antigenic activity of allergen extracts is proposed, making use of a rabbit antiserum. A dilution of the latter is selected which is inhibited by the allergen extract. The antigenic activity is then evaluated by radioimmunoassay with 125I-labelled protein A from Staphylococ- cus aureus as tracer. Key words: standardization -- RAIT -- antigenic activity -- allergenic extracts Introduction Much attention has been paid to development of adequate methods for standar- dizing allergen extracts. Methods based on protein content or Noon units, or weight of pollen by volume, are unsatisfactory since they may not correlate with biological activity. Several methods have been used to titrate the allergen activity in pollen extracts: RAST inhibition (Gleich et al., 1974), histamine release from human basophils (Baer et al., 1970), skin prick tests (Aas and Belin, 1972) and inhibition of passive cutaneous anaphylaxis in a mouse-to-rat system (Akiyama et al., 1979). Other methods used for analysis of the qualitative composition of extracts are crossed immunoelectrophoresis (L~wenstein, 1978), crossed radioimmuno- electrophoresis (Weeke and Lowenstein, 1973), rocket immunoelectrophoresis (Weeke, 1973), tandem crossed immunoelectrophoresis (Kr~ll, 1973) and fused rocket immunoelectrophoresis (Svendsen, 1973). Such techniques are subsumed as quantitative immunoelectrophoresis. Isoelectric focusing followed by RAST on isolated fractions (Varga and Ceska, 1972) with preparative isoelectric focusing has been used to assay the biological activity of the fractionated material (Topping et al., * Correspondence to: Dr. Luigi Di Berardino, c/o Lofarma Allergeni S.a.S., Viale Cassala 40, 201,13 Milan, Italy. 0022-1759/83/$03.00 © 1983 Elsevier Science Publishers B.V.