A hypothetical scheme for the pathogenesis and progression of immunoproliferative small intestinal disease and intestinal Burkitt lymphoma. Chronic C jejuni infection develops due to defective gut mucosal immunity. The cytolethal distending toxin of C jejuni may cause double-stranded DNA breaks in proliferating germinal center B cells that are even normally liable for mutations, deletions, and insertions. Truncated α heavy chain–producing plasma cells are selected due to the absence of variable determinants on the surface; they proliferate and progress resulting in IPSID. EBV infection in previously unexposed children may result in Burkitt lymphoma of the intestine. (A) Immunoselection, abnormal precipitation lines in patient's sera (1 and 2), and normal control showing precipitation around the trough (3). (B) Electron micrograph: IPSID neoplastic plasma cells with distended endoplasmic reticulum and intranuclear “inclusions” (Dutcher bodies). (C-D) Jejunal biopsies of early IPSID showing diffuse mucosal plasma cell proliferation with intact epithelium with sparse crypts (hematoxylin and eosin [H&E] stain). (E) Progressed IPSID mesenteric lymph node: lymphoplasmacytic and immunoblastic lymphoma (Giemsa stain). (F) Autopsy thickened intestinal wall along the whole length and enlarged mesenteric lymph nodes. The electron micrograph in panel B was taken with a Philips 100 electron microscope (Royal Philips Electronics, Eindhoven, Netherlands), original magnification × 2800. Light micrographs in panels C-E were taken with an Olympus BX50 microscope and an Olympus C-35AD4 camera (Olympus, Tokyo, Japan), at objectives of 10 ×/0.30 NA, 20 ×/0.50 NA, and 40 ×/0.75 NA (panels C-E, respectively). Images were processed with Adobe Photoshop (Adobe, San Diego, CA).