Ly49A receptor calibration in allogeneic recipients with chimerism levels above and below threshold. The expression of Ly49A on host NK cells was studied because B6 recipient mice are responsive to the MHC class Ia antigen H-2Dd that is highly expressed on the donor Balb/c hematopoietic cells. (A) Relationship between the frequency of Ly49A expression and the level of chimerism in B6 recipients. Y-axis values represent the frequency of receptor-bearing cells relative to reference values for age-matched noninjected controls (rFreq). (B) Relationship between the intensity Ly49A expression and the level of chimerism in B6 recipients. Y-axis represents the relative mean fluorescence intensity relative to naive animals (rMFI). Reference values for the frequency and intensity of Ly49A expression for naive animals is indicated by a dotted line.