Donor cell detection in host cells by staining with anti-β₂M^b immunecomplexes and quantitative FACScan cytometry. Spleen cells from DBA/2 hosts (A) or B10.D2 donors (D) or mixtures of 20% (B) or 80% (C) donor to host cells were stained. The percentage of recovered donor cells in gate M1 is indicated in parentheses.