Expression of functional cysteinyl leukotriene receptors by human basophils

Background: Synthesis of leukotriene (LT) C₄ by basophils and mast cells is an important component of IgE-mediated inflammation, resulting in increased levels of the cysteinyl leukotrienes (cysLTs) LTC₄, LTD₄, and LTE₄. Receptors for cysLTs are expressed on a variety of peripheral blood leukocytes, but of interest, they are also expressed on cells that synthesize LTC₄, such as eosinophils and mast cells. Objective: We examined human basophils for expression and function of cysLT receptor type 1 (cysLT1) and cysLT receptor type 2 (cysLT2). Methods: Basophils were purified from human blood and analyzed by means of RT-PCR, Western blotting, and flow cytometry for receptor expression. Basophils were also examined for functional responses to LTD₄, including cytosolic calcium flux, histamine release, viability, and chemotaxis. Results: We found that basophils express mRNA for cysLT1 and cysLT2. CysLT1 and cysLT2 were also detectable by means of flow cytometry, but only cysLT2 was detectable by means of Western blotting with available antibodies. Increases in cytosolic calcium induced by LTD₄-stimulated basophils were inhibited by the cysLT1 receptor antagonist zafirlukast, confirming the presence of functional cysLT1 receptors on basophils. There was no significant effect of LTD₄ on histamine release; however, LTD₄ decreased CD95 (Fas) expression on basophils in several-day cultures. Conclusions: We have demonstrated that basophils express the cysLT receptors cysLT1 and cysLT2, and some functional responses to LTD₄ can be observed.