Accumulated immune complexes of IgE and omalizumab trap allergens in an in vitro model.
The best understood mechanisms of omalizumab are that it neutralizes free IgE and down-regulates high-affinity IgE.Fc receptors (FcepsilonRI) on basophils and mast cells. It has been proposed that since complexes of IgE and omalizumab are accumulated to 5-10 times the basal levels of IgE, they may trap incoming allergens, contributing to omalizumab's effectiveness. In order to investigate the ability of IgE:omalizumab complexes in trapping allergens and inhibiting basophil activation in an in vitro reconstitution model, the ability of IgE:omalizumab complexes to tie up antigen and hence inhibit (a) antigen binding to IgE bound by FcepsilonRI, and (b) antigen-mediated activation of basophils, was examined. The free IgE was prepared by mixing different proportions of antigen-nonspecific IgE secreted by U266 cells and antigen-specific IgE, SE44 IgE, which recognizes a synthetic 15 a.a. peptide, R15K. The antigen was (R15K)(8)-ova, i.e. ovalbumin conjugated with an average of 8 copies of R15K per molecule. The solid-phase FcepsilonRI was a recombinant protein representing the extracellular portion of the alpha chain of the FcepsilonRI receptor complex. The model FcepsilonRI(+) basophilic cell line was RBL.SX-38, a rat basophilic leukemic line transfected with the genes for alpha, beta and gamma subunits of human FcepsilonRI. The results showed that the IgE:omalizumab complexes trapped increasing amounts of antigen with increasing (a) concentration of IgE, (b) proportion of antigen-specific IgE in total IgE, and (c) concentration of total immune complexes. Such trapping decreased the antigen-induced activation of FcepsilonRI(+) cells that had been pulsed with antigen-specific IgE, resulting in decreased mediator release. These results suggest that the rapidly accumulated IgE:omalizumab complexes in omalizumab-treated patients can capture allergens and consequently contribute to the pharmacological effects of omalizumab.
Institute of Molecular Medicine, National Tsing Hua University, Hsinchu, Taiwan.
Chuan-Long
CL
Hsu
Yu-Yu
YY
Shiung
Bai-Ling
BL
Lin
Hwan-You
HY
Chang
Tse Wen
TW
Chang
D000485:Allergens / Q000737:chemistry*; D000818:Animals; D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal / Q000737:chemistry*; D061067:Antibodies, Monoclonal, Humanized; D000936:Antigen-Antibody Complex / Q000737:chemistry*; D001491:Basophils / Q000187:drug effects / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D007073:Immunoglobulin E / Q000737:chemistry*; D007141:Immunoglobulin Fc Fragments / Q000378:metabolism; D000069444:Omalizumab; D051381:Rats; D013205:Staphylococcal Protein A / Q000737:chemistry; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism
D000485:Allergens; D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000936:Antigen-Antibody Complex; D007141:Immunoglobulin Fc Fragments; D013205:Staphylococcal Protein A; D000069444:Omalizumab; D007073:Immunoglobulin E; D001619:beta-N-Acetylhexosaminidases