RAST-inhibition studies of the imported fire ant Solenopsis invicta with whole body extracts and venom preparations

Whole body extracts of imported fire ants (IFAWBE) are the only reagents currently available for diagnosis and immunotherapy of patients with anaphylaxis to these Hymenoptera. To characterize better IFAWBE of the species Solenopsis invicta, we evaluated the sera of 29 patients with systemic or large local reactions to imported fire ant (IFA) stings. Forty-eight percent (14/29) of these sting-sensitive patients were IFAWBE RAST positive (greater than or equal to 6% binding of total radioactivity added). With a pool of sera with an initial IFAWBE-RAST value of 16.2% binding, we evaluated RAST inhibition by IFA venom (IFAV), IFAWBE, and the venom component, transpiperidine. Maximum RAST inhibition obtained was 84% with 300 micrograms/ml of IFAV, 95% with 5 mg/ml of protein IFAWBE, and insignificant with undiluted transpiperdine. We conclude that IFAWBE contains large quantities of immunoreactive venom components other than transpiperidine and that the allergenicity of IFAWBE and venom resides in the small amount of protein present in IFAV.