Regulation of surface CD3 levels on 3A9 TCR transgenic thymocytes on the B10k and NODk genetic backgrounds. 3A9 TCR transgenic mice on the B10k and NODk backgrounds were assessed for CD3 surface levels by flow cytometry, at both the DP and SP 1G12+ developmental stages. (a) Representative histograms for CD3 expression on DP cells and SP 1G12+ cells. B10k mice are shown in grey, NODk mice in white. (b) The mean fluorescence intensity (normalized to B10k SP 1G12+ thymocytes) and standard error is shown with B10k in black and NODk in white (n = 7 for B10 values, 17 for NOD values). Significance of differences between B10k and NODk groups of the same genotype are indicated by t-test p values about the group. t-tests comparing SP 1G12+ thymocyte expression were tested using a two sided t-test of the hypothesis that NODk expression levels are different to '100'.