Disruption of CD28 resulted in shorter survival and accelerated infiltration of CD3⁺ T cells in vital organs in Tgf-β1^-/- mice. (A) Survival curves of Tgf-β1^-/-/CD28^-/- mice and Tgf-β1^-/- mice (n = 7). A significant reduction in survival (P = .004 with log-rank test) was observed by the cross of Tgf- β1^-/- mice with CD28^-/- mice. (B) CD3 immunostained sections from liver, lung, and heart from 13-day-old Tgf-β1^+/+/CD28^-/- mice (i-iii), Tgf-β1^-/-/CD28^-/- mice (iv-vi), and Tgf-β1-/-/CD28^+/+ mice (vii-ix) are shown. Original magnification, × 400. Arrowheads indicate CD3⁺ T-cell infiltrates. (C) Expression of memory/activation markers on CD4⁺ and CD8⁺ T cells was not significantly altered by the disruption of CD28 in Tgf-β1^-/- mice. The percentages of CD62L^lowCD44high T cells are shown (n = 6 for Tgf-β1^+/+/CD28^+/+, Tgf-β1^-/-/CD28^+/+, Tgf-β1^-/-/CD28^-/-;n = 4 for Tgf-β1^+/+/CD28^-/-). (D) Disruption of CD28 resulted in CD8⁺ T-cell expansion in Tgf-β1^-/- mice (n = 10 for Tgf-β1+/+/CD28^+/+ and Tgf-β1^-/-/CD28^+/+ mice; n = 5 for Tgf-β1^+/+/CD28^-/- mice; and n = 7 for Tgf-β1^-/-/CD28^-/-). Percentages of CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells in spleens are shown.