The patient's anaphylactic reaction is determined to be mediated by antigen-specific IgE antibodies attached to high-affinity receptors on the surface of mast cells and basophils. Which of the following mechanisms is most likely to trigger vasoactive substance release by these cells?

Question

The patient's anaphylactic reaction is determined to be mediated by antigen-specific IgE antibodies attached to high-affinity receptors on the surface of mast cells and basophils.  Which of the following mechanisms is most likely to trigger vasoactive substance release by these cells?

Quizplus · Accepted Answer

11ec160b_379a_b603_9249_2b213a6722ca_MD0001_00 The high-affinity IgE receptor (FcεRI) is found on mast cells and basophils and plays a primary role in mediating the allergic response. The receptor normally binds the Fc portion of circulating IgE, coating the cell with various antigen-specific IgE molecules. When a multivalent antigen comes in contact with the cell, multiple IgE antibodies become cross-linked, resulting in aggregation of the FcεRI receptors on the mast cell surface. This clumping of receptors leads to the activation of non-receptor tyrosine kinases, triggering an intracellular cascade that ultimately results in mast cell and basophil degranulation. (Choices A and B) The high strength of the IgE-FcεRI bond is a result of the sum of many weak noncovalent forces; it is not associated with the formation of covalent (eg, disulfide, peptide) bonds. The strength of this attachment is such that antibody-receptor dissociation is rare; most of the total IgE in the body is bound to the surface of mast cells and basophils and not circulating freely. (Choice D) Receptor detachment from the cell surface is not a known mechanism of signal transduction. (Choice E) Receptor internalization occurs in the process of synaptic desensitization to excessive neurotransmitter stimulation. It also occurs in receptor-mediated endocytosis of substances such as iron (ie, transferrin receptor) and cholesterol (ie, LDL receptor). Educational objective: The high-affinity IgE receptor (FcεRI) is found on the surface of mast cells and basophils and normally binds the Fc portion of circulating IgE antibodies. Cross-linking of multiple membrane-bound IgE antibodies by a multivalent antigen results in aggregation of the FcεRI receptors, causing degranulation and the release of preformed mediators (eg, histamine, tryptase) that initiate an allergic response.

The Patient's Anaphylactic Reaction Is Determined to Be Mediated by Antigen-Specific