Interference in ragweed pollen and honeybee venom radioallergosorbent tests

We studied sera from patients sensitive to short ragweed (SRW) and honeybee venom (HBV) to investigate serum factors able to interfere with the measurement of IgE antibody levels by the radioallergosorbent test (RAST). We heated sera to destroy IgE antibodies and tested them for interference in the RAST. Heating sera for 4 hr at 56 degrees C destroyed up to 98% of the IgE antibody activity. After immunotherapy sera from patients sensitive to SRW and HBV produced striking interference in the RAST. The interference was most marked in the RAST employing 50-microgram quantities of microcrystalline cellulose-linked allergens, but it was also evident in the RAST employing 500-microgram quantities of such allergens and in the commercial RAST in which allergen is linked to paper disks. The interfering substance eluted from diethylaminoethyl (DEAE) cellulose in the IgG fraction. The interference could be eliminated by increasing the relative quantity of solid-phase allergen; RAST interference was not detected when SRW extract was linked to Sepharose 4B. The results indicate that serum factors, presumably IgG antibodies, produce interference in the RAST. Thus immunotherapy studies that measure IgE antibody levels by the RAST must consider the possibility that IgG antibodies can appear to depress IgE antibody levels. Furthermore, because commercially available RAST disks are susceptible to RAST interference, they must be used with caution for the diagnosis of allergy in patients whose sera may contain significant quantities of IgG antibodies.