Colitis is characterized by extensive infiltration of T cells and granulocytes. (A) Histologic analysis of colitis in B6 Rag recipients that received B6→Balb GVHD T cells, revealing marked infiltration of mononuclear cells into the lamina propria accompanied by depletion of goblet cells and sloughing of the mucosa into the colonic lumen along with (B) transmural inflammation extending out into the mesentery indicative of serosal inflammation (original magnification, × 200). (C) Neutrophils (dashed arrows) and eosinophils (solid arrows) in regions of histologically damaged colonic tissue. (D) Colonic mucosa in Balb-Rag recipients showing no evidence of colitis with preservation of goblet cells and the absence of inflammation in the lamina propria and muscularis mucosa. (E) Immunohistochemical staining showing extensive CD3⁺ T-cell infiltration (brown staining cells) throughout the lamina propria extending across the wall of the colon into the surrounding mesentery corresponding to sites of tissue damage in B6 Rag animals (ie, crypt abscesses, crypt cell apoptosis). (F) Absence of GVHD T-cell infiltration into the mucosa or lamina propria of Balb Rag mice. (G) Colonic tissue from B6 Rag recipients of B6→B10.BR spleen cells showing similar pathologic damage and (H) CD3⁺ T-cell infiltration as in panels A and E, respectively.