MS4a4B is expressed on the cell surface. NIH 3T3 cells or 58α T-hybridoma cells were infected with retrovirus encoding MS4a4B with an extracellular HA epitope tag or with an MIGR vector control. Viral transduction was detected by expression of green fluorescent protein (GFP). Cells were stained with anti-HA mAb and analyzed by flow cytometry. The inset numbers represent the percent of viable (propidium iodide-negative) cells in each quadrant. Results shown are representative of at least 5 separate experiments.