FITC-labeled Tat-dn-H-Ras enters eosinophils.

Tat-dn-H-Ras was labeled with FITC, as described in “Materials and methods.” Human blood eosinophils resuspended in pH 6.8 HBSS without calcium or magnesium and 1% fetal calf serum were incubated with 100 nM FITC-Tat-dn-H-Ras, and, at 5-minute intervals, aliquots were analyzed by flow cytometry on a FACScan (A). As a control for protein bound to the cellular exterior, FITC-labeled bovine serum albumin was incubated with eosinophils under identical conditions (B). Uptake of the control Tat-GFP protein is similar to that of Tat-dn-H-Ras (C). These histograms are representative of 3 independent experiments.