Accumulation of naïve T cells in the bone marrow of NOD mice. A. Frequency of CD4 T cells in the bone marrow of Balb/c, prediabetic and diabetic NOD mice. Cells from bone marrow (BM), spleen (SP) and pooled lymph nodes (LN, including cervical, mediastinal, auxiliary, brachial, mesenteric, and inguinal nodes) were stained for CD4, CD8, TCRβ, and PI. CD4 versus TCRβ profiles are shown for live cells. The numbers indicate the percentages of CD4+TCR+ cells in the gated regions. p < 0.001 comparing percentages of CD4 T cells in the bone marrow between Balb/c and NOD mice. B. The average number of CD4 (open bar) and CD8 (solid bar) T cells in the BM, LN and SP of Balb/c (n = 22), prediabetic (n = 19) and diabetic (n = 16) NOD mice. p < 0.01 comparing CD4 or CD8 T cells in the bone marrow between Balb/c and prediabetic or diabetic NOD mice. C. Increase of percentages of CD4 T cells with age in the bone marrow of diabetic NOD mice. The r2 value is 0.76. D. Inverse correlation between percentage of CD4 T cells in the bone marrow and CD4 T cell number in the spleen of the same diabetic NOD mice. The r2 value is -0.69. Data presented in C and D are from the same group of mice. One dot represents one mouse. E. Comparison of percentages of CD4 T cells in the bone marrow of 4–5 week old BLAB/c (n = 6) and NOD (n = 8) mice. p < 0.001. F. Comparison of percentages of CD4 T cells in the bone marrow of 6–9 week old Balb/c (n = 5), EA16 (n = 3) and NOD (n = 8) mice. p < 0.001 comparing Balb/c to NOD (or EA16) mice. G. Phenotype of bone marrow T cells. Bone marrow cells were stained for TCR, CD4, CD25 plus CD45RB, or for TCR, CD4, CD44 and CD45RB. Representative plots from at least four independent experiments are shown, gating on CD4+TCR+ cells.