Assay methods for measurement of mediators and markers of allergic inflammation

With the discovery of immunoglobulin E (IgE) as the source of reaginic activity in serum, the release of histamine from leukocyte suspensions challenged with a specific antigen has been used as a reliable in vitro correlate of immediate hypersensitivity. Although histamine remains the most commonly measured mediator released following this IgE-mediated reaction, it is now well established that other mediators are also released from basophils and are important markers of allergic inflammation. This chapter highlights the growing interest in the use of flow cytometry assays to monitor activation-linked markers (e.g., CD63, CD69, and CD203c) on basophils and the applicability of such assays as surrogate indicators of mediator release. The radioenzymatic assay (REA) has the advantage of detecting very low levels of histamine, with a sensitivity of approximately 10 pg/ml. The REA is not subject to interference from high protein levels, which makes it an excellent protocol for measuring plasma histamine levels. Measurement of the release of preformed histamine from peripheral blood basophils challenged with a specific antigen is among several tests available, and histamine release remains a valuable in vitro correlate of immediate hypersensitivity reactions. Mediators such as LTC4 and IL-4, are generated by basophils upon IgE-dependent activation, and in vitro assays have recently been developed to measure these products. These assays, combined with those available for the detection of several other mediators occurring in biological fluids, have produced data that have significantly added to our understanding of the parameters, mechanisms, and pharmacologic control of allergic inflammation.