Lymphoproliferative disease, patient 2. (a) Donor ileum, day 24; rejection. Severe cellular rejection is represented. Fragments of residual epithelium are seen, and a mixed cellular infiltrate is presented in the lamina propria, × 160. (b) Donor ileum, day 34; lymphoproliferative disease. The infiltrate is more exuberant, more monotonous, the cells are larger, and the infiltrate obscures anatomic boundaries such as the muscularis mucosae, × 160. (c) Ileum, day 34. Frozen section stained with donor specific antibody Bw6 stains endothelial cells and epithelial remnants, × 300. (d) An adjacent section stained with recipient-specific antibody HLA 25/32 highlights the infiltrating lymphoid cells. The pattern does not distinguish rejection (see Fig. 4) from the lymphoproliferative process, ×300.