Inducing an anergic state in mast cells and basophils without secretion

Background: IgE-mediated secretion from mast cells or basophils depends on the activity of both spleen tyrosine kinase (syk) and phosphatidyl inositol 3′ kinase (PI3K), but several specific downregulatory pathways (eg, loss of syk expression) do not. Objective: We tested whether stimulation with antigen in the presence of a syk inhibitor (NVP-QAB205) would ablate secretion while simultaneously allowing anergy. Methods: The anergic or desensitized state in human basophils, cultured-derived mast cells, and in situ stimulated airway mast cells (in organ baths) was assessed after stimulation with antigen in the presence of syk inhibitor. Results: Antigen caused 35 ± 7% and 62 ± 10% histamine release from basophils and mast cells, respectively, and it caused an 87 ± 5% histamine/leukotriene D₄-dependent contraction of human isolated bronchi. All of these responses were blocked >95% by the syk inhibitor. Rechallenging the preparations with antigen, after first washing out the syk inhibitor and antigen, revealed that near complete anergy (92% to 100%) occurred in each case. A similar result was found when using a PI3K inhibitor, LY294002, in studies of basophils. Conclusion: Although the syk inhibitor nearly abolished the antigen-induced secretion from mast cells and basophils, it had little effect on the pathways involved in anergy. These results suggest that syk and PI3K are not involved in downregulation leading to anergy.