Myeloid and B cell in C57Bl/6 → (BALB/c × C56Bl/6)F1 chimeras are of donor origin. PEC and spleen cells obtained from C57Bl/6 → (BALB/c × C57Bl/6)F1 or (BALB/c × C57Bl/6)F1 were stained with fluorescein isothiocyanate–labeled 34-4-21S (anti-D^d) and 14-4-4 (anti-I-E^k,d) antibodies, respectively, and analyzed by FACS.