Abstract: The present invention provides methods and compositions for treating or preventing allergic reactions, particularly anaphylactic reactions. Methods of the present invention involve administering microorganisms to allergic subjects, where the microorganisms contain a recombinant version of the protein allergen. The recombinant version can be wild-type or may include mutations within IgE epitopes of the protein allergen. Preferably the compositions are administered rectally. Particularly preferred microorganisms are bacteria such as E. coli. Any allergen may be used in the inventive methods. Particularly preferred allergens are anaphylactic allergens including protein allergens found in foods, venoms, drugs and latex. The inventive compositions and methods are demonstrated in the treatment of peanut-induced anaphylaxis.