Assessment of IgE-mediated sensitivity during immunotherapy: comparison of the RAST with and without adsorption of IgG to titrated prick skin tests.

The effect of specific IgG induced by allergy immunotherapy on specific IgE binding in the RAST was assessed by removal of the IgG with staphylococcus protein A bound to Sepharose. In sera from those patients with the highest titers of specific IgG, RAST binding was increased 8% following adsorption of the post-immunotherapy sera while in sera obtained from the same patients before immunotherapy adsorption increased binding only 3%. The effect of allergy immunotherapy on the titrated prick skin test was compared to the effect on the RAST to the same allergen. In nine patients who received the highest dose of grass extract, the area of the titrated prick skin tests was reduced following immunotherapy by 75%. Staphylococcus protein-A adsorption of sera from these patients drawn before immunotherapy resulted in an increase in RAST binding of 2.7% compared to an increase of 6% in sera obtained after immunotherapy, suggesting suppression of RAST binding of only 3% by specific IgG. It is concluded that RAST levels are affected less than prick skin tests by the immunologic response to allergy immunotherapy. Some interference in RAST binding is produced by specific IgG antibody in high titers, but for many critical purposes the degree of interference is not significant.