In the Phase I study we successfully identified a bacterial binding protein that bound selectively to human IgE in a non-immune manner. This purified binding protein has the potential to act as a tracer for human IgE without interference from other human plasma proteins like lgG, IgM or albumin that are present in large molar excess. The bacterial protein can capture human lgE when immobilized and can be biotinylated without loss of functional activity. These properties suggest that this protein can act as a protein A or protein G equivalent bacterial-binding protein for IgE. This bacterial protein has the potential to replace current second antibody reagents specific for the epsilon heavy chains that are currently used for allergy testing in clinical laboratories. There are many advantages of the bacterial tracer over the current antibody reagents that include ease of preparation, ability to readily modulate affinity and the economics of production. The Phase II proposal is designed to further characterize the bacterial IgE-binding activity and develop efficient expression and purification protocols for the wild type protein and finally, optimize the use of the IgE-binding protein in selected assays for total and allergen specific lgE. PROPOSED COMMERCIAL APPLICATION: Allergic rhinitis has been estimated to lead to 10 million physician office visits/year in the U.S. The total cost of allergic rhinitis in 1994 was estimated at $1.23 billion in lost productivity. In 1993 the cost for physicians visits and over the counter and prescription medications was estimated at $2.4 billion. Allergy testing, in the clinical laboratory, represents a major market. Laboratory assays to detect IgE response to specific allergens with increased sensitivity and reduced false negative results would be advantageous.