RBL cells expressing human Fc qRI are a sensitive tool for exploring functional IgE–allergen interactions: studies with sera from peanut-sensitive patients Donald A. Dibbern Jr., G. William Palmer, P. Brock Williams, S. Allan Bock, Stephen C. Dreskin * Division of Allergy and Clinical Immunology, University of Colorado Health Sciences Center, Medical School Building, Room 4627, 4200 East 9th Avenue, Denver, CO 80262, USA The National Jewish Medical and Research Center, Denver, CO, USA Received 9 April 2002; received in revised form 24 July 2002; accepted 27 August 2002 Abstract Rat basophilic leukemia cells (RBL SX-38) express the a, h, and g chains of human FcqRI. Following sensitization with IgE from a subset of allergic human donors, these cells can be triggered by exposure to anti-IgE or to very low concentrations of specific allergens. We examined 18 sera from patients who were highly sensitive to peanuts by history and had anti-peanut IgE by in vitro testing. The ability of these sera to sensitize the RBL SX-38 cells for degranulation with peanut allergens correlates very well with the absolute amount of anti-peanut IgE (r = 0.95; p < 0.001). The most effective sera contained at least 50 kU/l of total IgE and at least 15 kU/l of peanut-specific IgE. RBL SX-38 cells sensitized with these sera degranulated optimally upon exposure to anti-IgE (net degranulation of 40 F 8%, means F S.D.; n =8) and to a 10 5 –10 6 dilution of crude peanut extract (CPE) (37 F 7% net degranulation; 93 F 13% of that seen with anti-IgE). This assay is quite sensitive. Cells sensitized with selected sera are activated by exposure to a 1:10 7 dilution of the CPE containing picogram amounts of peanut allergens. This assay is also quite specific. Cells sensitized with sera from patients with anti-peanut IgE and no detectable IgE against soybean, walnut or grass pollen did not degranulate following exposure to these latter antigens. The converse was also true; cells sensitized with sera from patients without anti-peanut IgE did not react to peanut. These data demonstrate that RBL cells expressing human FcqRI form the basis of a useful model system for the detection of allergens and for the study of IgE – allergen interactions. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Peanut allergy; RBL SX-38 cells; Allergen assay; Anaphylaxis; Mast cells 1. Introduction Type I immediate hypersensitivity reactions are mediated through the effects of antigen-specific IgE. IgE binds to high-affinity receptors for IgE (FcqRI) on human mast cells and, when cross-linked by antigen, 0022-1759/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0022-1759(02)00369-1 Abbreviations: RBL-2H3 cells, rat basophilic leukemia; RBL SX-38 cells, RBL-2H3 cells expressing human Fc qRI; Fc qRI, Fc- epsilon receptor I; IgE, immunoglobulin E; kU, kilounits; CPE, crude peanut extract. * Corresponding author. Tel.: +1-303-315-6979; fax: +1-303- 315-7642. E-mail address: Stephen.Dreskin@UCHSC.edu (S.C. Dreskin). www.elsevier.com/locate/jim Journal of Immunological Methods 274 (2003) 37 – 45