REL and MALT lymphoma: In addition to the epithelial pathology described above, half (3 of 6) of the c-Rel−/− mice exposed to H. felis for 1 year also developed lymphoproliferative lesions similar to, but less severe than the low-grade MALT lymphoma-like lesions identified in BALB/c mice by Enno et al.22 These lesions were characterized by marked gastric lymphoid hyperplasia, with large, highly proliferative (Ki67+ cells) and disorganized multifocal to coalescing lymphoid follicles (Figures 9a and b).