Surface phenotype of cells developing in the fetal thymus lobe culture. Fetal thymocytes from C57BL/6-Ly5.1/C57BL/6-Ly5.2 F1 mice (Ly5.1/Ly5.2) were plated in methylcellulose culture with SF, IL-7, and IL-15. After 14 days of culture, immature NK cell colonies were individually picked, pooled, and incubated in hanging drops for 20 hours with fetal thymus lobes from BDF1 (Ly5.2) mice. The lobes were cultured on filter membranes for an additional 8 days. Cells recovered from the lobes were stained with MoAbs specific for molecules indicated in each FACS profiles. (A) Expression of Ly5.1 (donor marker) by the cells from cultured lobes. (B) Expression of NK1.1 and CD3 by donor-derived cells. Only the gated cell population (R1) is shown in each FACS profile. Dotted and solid lines represent cells stained with isotype-matched Ig and specific MoAbs, respectively.