Particle counting immunoassay of immunoglobulin E antibodies after their elution from allergosorbents by pepsin: an alternative to the radioallergosorbent test.

The absorption of specific antibodies on allergen-coated cellulose discs, followed by pepsin digestion to release the IgE Fc" fragment, which is then assayed by particle counting immunoassay (PACIA), is a new practical and reliable method to quantitate IgE antibodies and to standardize allergens. The coefficient of variation of repeated assays does not exceed 12.8% and the correlation coefficient with RAST was r = 0.96. Some discrepancies could be explained by differences in the antiserum specificities and the presence of anti-IgE autoantibodies. The determination of IgE antibodies by PACIA offers the following advantages: (1) no radioisotopes; (2) stability of reagents, since antibody-coated latex particles and the standards keep their activity for more than 1 yr; (3) low cost of reagents due to ease of preparation --PACIA does not require purified antibodies to measure IgE but only F(ab')2 fragments of the IgG fraction of the anti-IgE antiserum to coat latex; (4) avoidance of nonspecific absorption of the labeled anti-IgE on the solid phase; (5) prevention by elution of the inaccuracies observed in RAST at very high titers of IgE antibodies; (6) expression of the results in international units per milliliter to calculate the ratio of specific IgE Ab vs total IgE, with a high ratio suggesting that the patient is sensitive to a few allergens; (7) standardization of allergenic extracts; and (8) the particular specificity of the anti-IgE antiserum directed against a heat- and protease-resistant fragment of IgE.