Diethyltoluamide (DEET) increases CD63 expression in a contact urticaria patient's basophils.

The use of insect repellent has increased during recent years to prevent insect stings and its feared consequences of virus and parasitic diseases transmitted by infected mosquitoes and tick bites. DEET (N, N-diethyl-3-toluamide) is the most effective and most widely-used insect repellent and it is used by approximately 30% of the population. The DEET Registry is a post-marketing surveillance system which has collected voluntary reports of different and infrequent moderate to severe adverse events to this drug, including seizures and other neurological symptoms, dermal rashes and other systemic manifestations. Hives, rashes, itching, redness and swelling after exposure were detected in 85 (35%) out of 242 cases. Hypersensitivity reactions manifested as contact urticaria and anaphylaxis, after brief contact with DEET, have also been described as case reports. In some patients with hypersensitivity to the product, skin test with DEET induced a typical immediate wheal and flare reaction. Furthermore, passive human sensitisation was reported positive, suggesting an IgE mediated phenomena. However, a skin test negative patient has also been reported. Contact urticaria has been described for a number of stimuli. Allergens from shrimp or latex react through an IgE mediated reaction, while others, like water induced urticaria or contrast media reactions, are unlikely to represent an IgE mediated response. Flow cytometry detection of basophile activation has been utilised previously for the diagnosis of allergy. Basophile activation test (BAT) takes advantage of CD63 over expression by activated basophiles. It has been described as a useful tool to explore the capacity of a substance to mediate cell activation and to suggest the possible mechanistic way of cell degranulation. Furthermore, for a number of allergens, IgE induced-basophile degranulation has been well documented. However, for pseudo-allergens, like non-steroidal anti-inflammatory drugs, basophile activation does not seem to increase CD63 or other cell membrane markers expression. So, BAT response of basophiles from a sensitive patient to DEET may contribute to our understanding of the physiology of DEET hypersensitivity reaction. A 50-year-old woman consulted with a history of an urticarial reaction to DEET-based insect repellents. She stated that a few minutes after either spray, aerosol or lotion product application, an urticarial rash appeared on the exposed areas. She tried several different brands of repellent with the same result. Since she frequents a mosquito-infested zone she decided to consult. An openlabel challenge was performed spraying a DEET containing product on her right antecubital fossae. In a few minutes, an urticarial and pruriginous rash developed which lasted for 60min. We evaluated the CD63 and CD11b expression on basophiles from the patient after incubation of 100 l of Table 1 BAT results: Percentages of basophiles expressing CD63 or CD11b in the DEET sensitive patient and a tolerant donor.