Histopathologic changes in the colon and small intestine of lethally irradiated host 7 days after the injection of donor cells. All hosts received 0.125 × 10⁶ CD4 ⁺ T cells and/or 2 × 10⁶ TCD bone marrow cells. (A) Colon of a control host given only TCD bone marrow cells. Arrows show mucin-containing goblet cells. (B) Colon of a host given WT CD4⁺ T cells and 2 × 10⁶ TCD bone marrow cells. An asterisk indicates infiltrate in area of crypt drop-out; and arrow, crypt abscess. (C) Colon of a host given CD62L^-/- CD4⁺ T cells and TCD bone marrow. An asterisk indicates inflammatory infiltrate and crypt drop-out. (D) Colon of a host given β₇^-/- CD4⁺ T cells. Inflammatory infiltrate and crypt drop-out are present. (E) Colon of a host given CD62L^-/-/β₇^-/- CD4⁺ T cells. Goblet cells are retained in crypt walls (arrow), and crypt drop-outs with infiltrate are minimal. (F) Small intestine of a host given WT CD4⁺ T cells. Villi are intact and infiltrate is minimal. Tissue sections were stained with hematoxylin and eosin; original magnification × 300. Each panel is representative of each of 3 hosts examined.