Antigen-Induced Reduction in Mast Cell and Basophil Functional Responses due to Reduced Syk Protein Levels

Abstract

Background: The high-affinity IgE receptor, FcεRI, is unresponsive on mast cells and basophils from people in several populations through an unknown mechanism. Similarly, FcεRI-positive basophils from ‘nonreleasers’ are IgE-unresponsive and are deficient in the tyrosine kinase Syk. Objective: To test the hypothesis that cross-linking FcεRI on mast cells and basophils leads to FcεRI nonresponsiveness through reduction in Syk protein levels. Methods: Human mast cells and basophils were used to determine if FcεRI hyporesponsiveness correlated with reduced Syk levels. Results: It is shown that suboptimal antigen challenge, that did not lead to significant mediator release, induced nonresponsiveness and correlated with reduced Syk. Other IgE-associated signaling molecules were unaffected by the same treatment. The ability of IgE-unresponsive mast cells to regain FcεRI responsiveness is paralleled by increased cellular Syk levels in vitro. The reduction of Syk levels with suboptimal antigen concentrations was calcium independent and mediated through a proteasome-dependent mechanism. Conclusion: These findings confirm and extend our knowledge about a novel regulatory mechanism for maintaining FcεRI in a quiescent state. This mechanism may also explain why low concentrations of allergen given to patients during allergen immunotherapy induce FcεRI nonresponsiveness and therapeutic benefit without inducing systemic anaphylaxis.

Effects of Novel Nanomaterials on Allergic Mediator Release from Human Mast Cells and Basophils through Non-Ige Mediated Pathways

“…All MC studies were approved by their Human Studies Institutional Review Board. Mast cells were purified and cultured as described [10,11]. Peripheral blood basophils were obtained from normal donors (no medications) after informed consent as approved by the Institutional Review Board, Johns Hopkins University and purified to >90% as described previously [12].…”

Antigenic Determinants of the Bilobal Cockroach Allergen Bla g 2

“…Fresh samples of skin tissue were cut into 1-2-mm fragments and incubated multiple times in a solution of tissue-digesting enzymes, as described previously (26). After purification, mast cells were sensitized overnight with allergen-specific IgE-containing serum (1:10 -1:100 dilutions depending on IgE titer).…”

“…After determining optimal sera and concentrations (F1 and G1; 1:10), cells were washed and challenged with varying concentrations of rBla g 2, mutants or positive controls for 20 min. ␤-Hexosaminidase release was measured in the supernatants obtained as described previously (26,27). Experiments included positive controls (anti-Fc⑀RI antibodies and wild type antigens), untreated cells (spontaneous), and increasing doses of rBla g 2 mutants (N93Q, Lys-132, Lys-251, F162Y, KK, and KKF; 0.001-20 g/ml).…”

Immunotherapy in allergy and cellular tests

“…A subthreshold desensitization of basophils following the induction of allergy tolerance may lead to loss of Syk and cell surface FcεRI. 66,67 Both FcεRI membrane recycling and the downstream receptor associated tyrosine kinase signaling, depend on substimulatory or long lasting allergen doses. Kinetics of antigen binding on FcεRI/IgE complex has been reviewed in the past [68][69][70][71][72][73][74] and may give an interpretation to the complex responsive pattern expressed by basophil during AIT.…”