Kinetics of Ly49A calibration and development of tolerance in prenatal chimeras above and below chimerism threshold. (A) The relative intensity (rMFI) of Ly49A expression at 3, 6, 9, and 12 weeks is plotted for subthreshold chimeras (0.3%-1.8% PB chimerism) and chimeras above threshold (> 1.8% PB chimerism), and comparisons are made relative to nonchimeric littermate controls (< 0.3% PB chimerism; *P < .05, **P < .01). Data points represent the mean rMFI plus or minus SEM at each time point. (B) NK-cell tolerance as a function of CD107a cell surface expression is shown reported as percentage specific expression. Comparison is made between prenatal allogeneic chimeras above and below chimerism threshold in response to syngeneic (B6.Ly5.1), donor-specific allogeneic (Balb/c), and third-party allogeneic (C3H) target cells (*P < .05).