A Solid Phase Radioimmunoassay for the Quantitation of Human Reaginic Antibody against Ragweed Antigen E

Abstract

IgE antibody directed against antigen E (AgE) of ragweed extract was measured quantitatively in the sera of 15 ragweed sensitive patients before initiation of immunotherapy. The assay employed polystyrene tubes which were successively coated with myeloma IgE and excess rabbit anti-IgE. This matrix which was specific for IgE bound IgE from the patients' serum in a reproducible and measurable manner. Radiolabeled AgE then reacted quantitatively with IgE antibody from the patients' serum which was attached to the solid phase. A double antibody method was developed simultaneously and gave comparable results for sera assayed by both procedures. Total serum IgE and the dose response of histamine release by AgE from washed leukocytes of the patients were also determined. The concentration of IgE anti-AgE in the 15 sera ranged from 3.2 to 400 ng/ml by polystyrene tube assay. Serum IgE ranged from 82 ng to 6 µg/ml and the percentage of the serum IgE specific for AgE varied from 0.3 to 41. Leukocyte sensitivity measured by the reciprocal of the minimum concentration of AgE resulting in release of 50% of the total histamine encompassed a 300-fold range. The level of IgE antibody to AgE was not correlated significantly with total serum IgE. Cell sensitivity varied independently of total serum IgE or nonspecific IgE. A highly significant correlation was found between IgE anti-AgE and cell sensitivity. Leukocyte sensitivity was found to be an exponential function of the serum antibody concentration.