ATRs are classically thought of as Type I hypersensitivity reactions due to immunoglobulin (Ig)E antibodies interacting with allergens to activate mast cells and basophils, but the etiology of ATRs has not yet been fully established. Both the plasma component and the recipient have been shown to play a role in ATRs. The primary mediators of anaphylaxis are biogenic amines (e.g., histamine, adenosine), eosinophil and neutrophil chemotactic factors, enzymes (e.g., proteases), bradykinin, and proteoglycans (e.g., heparin).5 However, specifc recipient characteristics may also be involved. For example,patients with IgA defciency are especially prone to anaphylaxis after blood transfusion if they have existing classspecifc anti-IgA.5-8 While the general mechanism of Type I