Detection of Basophil Activation by Flow Cytometry in Patients with Allergy to Muscle-relaxant Drugs

Abstract

ALLERGIC or pseudoallergic reactions that occur during anesthesia have been increasing over the last few years. 1 Muscle-relaxant drugs are responsible for at least half of these life-threatening adverse reactions. 1,2 The diagnosis of drug allergy is mainly based on a detailed clinical history, positive skin tests, and detection of specific immunoglobulin E (IgE). Nevertheless, the biologic results are not always closely correlated with clinical assessment of the disease, and discrepancies between skin tests and specific IgE are reported, 2,3 In these cases, in vitro investigations to identify the responsible drug are needed, and the histamine release (HR) test is usually performed. 2 HR reflects basophil degranulation, but the very small number of circulating basophils is a limitation to this test, and its clinical benefit remains controversial. Because flow cytometry is a valuable tool for identifying cell populations even at low concentrations, we developed a tricolor flow cytometric method (FCM) for the study of allergen-induced basophil activation. 4 Briefly, identification of basophils is based both on CD45 expression (a common leukocyte antigen) and on the presence of IgE on the cell surface, because basophils express high-affinity receptor for IgE. Cell activation on allergen or drug challenge is assessed by the expression of CD63 on the plasma membrane. 5 After the publication of preliminary data (only focused on usual allergens), we initiated studies to evaluate the usefulness of the method in the diagnosis of drug allergy. We report here results of the first four cases of allergy to muscle-relaxant drugs since this FCM was introduced in our laboratory. The patients were recruited from different associated hospitals in Lyon, France, and rapidly developed clinical features evocative of anaphylactic reaction after induction of anesthesia, e.g., hypotension, bronchospasm, and cutaneous signs. Investigations of the responsible drug were performed in the outpatient unit of the Department of Anesthesia (screening for drug allergy unit) at least 2 months after the allergic reaction. Skin prick and intradermal reaction (IDR) tests 3 were performed using various dilutions of drug solutions, specific IgE antibodies (against ammonium group) were measured using radioallergosorbent techniques (Capsystem; Pharmacia, Uppsala, Sweden), histamine was measured using a radioimmunoassay (Immunotech, Marseille, France), and HR test was considered positive when superior to 10% of total HR. Basophil degranulation by FCM was detected by CD63 expression on the cell surface. A positive threshold is defined with a negative control without any drug. Results are positive when > 10% of basophils express CD63.