Human blood eosinophils express Notch receptors. (A) Total RNA extracted from freshly isolated human eosinophils from 3 separate donors was reverse transcribed, and cDNA was probed by real-time PCR for Notch receptor 1 and 2 mRNA expression. neg, no RNA-negative control. Table includes average Ct values for N1 and N2 for comparison with 18S housekeeping controls. Intact (B) or saponin-permeabilized (C) eosinophils were analyzed by flow cytometry for expression of surface or intracellular Notch receptors, respectively. Shaded histogram represents isotype control. (D) Freshly isolated eosinophils were processed for immuno-EM with Abs against Notch receptor 1. Notch 1 expression was observed at the plasma membrane (Di) and within granules (Dii). Bars represent 1 μm (D) and 480 nm (Di,ii). Nu indicates nucleus.