CD2 expression level on CD4⁺CD8⁺ thymocytes in TCR transgenic mice is influenced by the MHC of the thymus. Thymocytes from the indicated mice were stained with phycoerythrin-labeled anti-CD4, fluorescein isothiocyanate-labeled anti-CD8, and biotinylated MoAb specific for CD2 followed by Streptavidin Tricolor and analyzed in the FACScan flow cytometer. A total of 30,000 events were collected. The contour plots indicate CD4 (FL2) and CD8 (FL1) expression levels by thymocytes from the indicated TCR transgenic mice on different MHC backgrounds with or without the CD2 null mutation (CD2^o). The histograms directly below the individual contour plots denote CD2 expression level (X-axis) of CD4⁺CD8⁺ thymocytes (R2 gate) from the indicated mice. The Y-axis of the histograms denote relative cell number.