Identification of CRTH2 expressing cells by flow cytometry. Left histogram : ungated leukocytes biparametric representation on the basis of side scatter characteristics (SSC, Y axis) and FITC-CRTH2 (X axis). Two CRTH2 expressing cell populations are easily distinguishable: the one with high light scatterings corresponds to the eosinophil population; the second one (gating region: A) comprises Th2 lymphocytes and basophils. Right histogram: cells from the gating region (A) expressed on the basis of PE-CD203c (X axis) and PC5-CD3 (Y axis) characteristics. Th2 lymphocytes were readily separated from basophils based on their positive CD3 expression while activated basophils express high levels of CD203c without expressing CD3.