APRIL production by tissue macrophages. Sections are from normal gastric mucosa (A), WI grade 5 (B,D-F) and grade 1 (G-L). Compared with normal gastric mucosa where APRIL reactivity is observed in rare large cells of the lamina propria (A), numerous APRIL⁺ cells are found (B-C) surrounding CD20⁺ neoplastic cells in MALT lymphoma (panel B inset) [red symbol in panel C indicates significance vs normal and G/HP- (#P < .01) or vs mWI-5/PT (##P < .01)]. Double staining demonstrates that APRIL⁺ cells coexpress CD11c (D), CD68 (E), and CD163 (F). No APRIL reactivity is observed in neoplastic B cells (B,D-F). In WI grade 1, the anti-HP antibody recognizes bacilli in the gastric mucous layer (panel G inset); HP reactivity is also observed in the cytoplasm of numerous cells in the gastric lamina propria (H). Double stain demonstrates that HP-containing cells are represented by macrophages coexpressing CD11c (I), CD163 (J), and CD68 (K) and some of them produce APRIL (L). For immunohistochemistry, sections are counterstained with Meyer haematoxylin and secondary antibodies revealed with DAB (brown, anti-APRIL in panels A,BD,E,F,L; anti-HP in panels G-K), and Ferangi blue (blue, anti-CD11c in panels D,I; anti-CD68 in panels E,K; anti-CD163 in panels F,J; APRIL in panel L). Scale bar: 100 μm (panels A,B,G) and 20 μm (panels D-F,I-L). Legend in panel C: G/HP- indicates HP-negative gastritis; mWI-5, matched WI-5; and mWI-5/PT, matched WI-5 posteradication treatment.