Immunologic and clinical responses to parenteral immunotherapy in peanut anaphylaxis--a study using IgE and IgG4 immunoblot monitoring.

BACKGROUND: Specific desensitisation to food allergens, which produce anaphylaxis after ingestion, has not been considered as a treatment for food allergy until recently. The purpose of this study was to assess if a parenteral immunotherapy program, using a partially characterised crude peanut extract, could induce a state of immunological tolerance in a patient who exhibited anaphylaxis, asthma and urticaria on exposure to peanut and other legumes. A further aim was to measure the serum antibody responses to the immunotherapy. METHODS AND
RESULTS: We report the successful desensitisation towards all of the legumes tested of a male patient on parenteral immunotherapy using a partially characterised peanut extract. The immunologic parameters measured during treatment included specific IgE and IgG4 for peanut, soybean, pea and lentil extracts. Immunoblots of specific IgE and IgG4 were made before and after therapy. The antibody response followed the same pattern seen in successful desensitisation of patients with bee venom anaphylaxis. The IgG4 levels increased strongly from a low pre-treatment level in proportion to the antigen dose received. The antigen-specific IgE levels gradually fell from a high pretreatment level, but remained significantly elevated. Immunoblotting for specific IgE and IgG4 demonstrated that acquisition of clinical tolerance after therapy was associated with declines in the number and intensity of bands in IgE blots and the development of more bands of increasing density in the IgG4 blots.
CONCLUSIONS: Parenteral immunotherapy may offer an alternative treatment to lifelong dietary restriction and epinephrine injections in patients who exhibit life-threatening IgE-mediated anaphylaxis to peanut. Cross desensitisation to other legumes appears to have occurred in this study. The quality and potency of the extract used is an important factor in achieving the desired acquisition of clinical tolerance. In our patient this tolerance correlated with his ability to maintain high levels of specific IgG4, which acted as a marker of protection against anaphylaxis. The use of IgG4 immunoblotting may provide an improved level of discrimination in the assessment of correlation of clinical efficacy with the immunologic response.