An Automated Particle Counting Immunoassay (PACIA) for Determination of Blocking Antibodies against Timothy Grass Pollen in Sera from Desensitized Allergies

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Abstract
An automated particle counting immunoassay (PACIA) for measurement of blocking antibodies (antigen neutralizing capacity) against timothy grass pollen extract in sera from desensitizd allergics is described. Latex particles coated with F(ab'')2-anti-timothy are agglutinated by timothy. Serum containing anti-timothy antibodies inhibits the agglutination. Non-agglutinated particles are counted in a modified AutoCounter. Of 20 sera from timothy allergics who had undergone immunotherapy with purified timothy extract for 30 wk, 19 showed significant agglutination-inhibition. None of 42 normal human sera gave significant inhibition. The inhibiting antibody could be removed by absorption with protein A and was thus of non-IgE nature, i.e., blocking antibody. The results obtained correlated statistically significantly with those found with a double-antibody method (rS = 0.62, n = 20, t = 3.35, P < 0.01) and with the cumulated dosage of timothy allergen extract administered to the individual patient (rS = 0.56, n = 20, t = 2.87, P < 0.02). Between-assay coefficient of variation was 6.4-18.3%. The capacity is 40 samples/h. The method has also been applied to measurement of blocking antibodies to honey bee and wasp venom.