Murine MALT lymphoma cells proliferate in response to Helicobacter antigen. (A-B) Histopathology of murine mucosa-associated lymphoid tissue (MALT) lymphoma. Consecutive paraffin sections were stained with hematoxylin and eosin (H&E), the B-cell marker B220, and the proliferation marker PCNA; representative sections are shown for an unaffected area (A) and a lymphoma (B) from the same stomach. (C-F) Single-cell suspensions of 9 murine MALT lymphomas were cultured in the presence or absence of 10 μg/mL Helicobacter felis lysate. The proportion of CD19⁺ B cells and CD3⁺ T cells was determined flow cytometrically for each culture (C). Proliferation was determined by [³H]-thymidine incorporation (D) or BrdU incorporation (E) after 5 days of culturing. Individual cultures and/or averages of all cultures are shown. Error bars represent SD. (F) The BrdU⁺ cells are mostly B and T cells.