Histologic analysis of B-cell tumor types. Representative hematoxylin and eosin (HE) and PNA-stained sections of mouse spleen from wild-type and IµHABcl6 mice with lymphoma from indicated genotypes. Wild-type mouse spleen is composed of white pulp with follicles (*) and a distinct marginal zone (arrowheads) separated by distinct areas of red pulp (**) with scattered PNA⁺ cells within follicles and the red pulp. In contrast, mice with lymphoma have marked expansion of the white pulp (*) with little or no visible red pulp (**). Neoplastic lymphocytes from IµHABcl6 and IµHABcl6 Ung^−/−Msh2^−/− mice are large and pleomorphic with abundant cytoplasm and are frequently PNA⁺ (arrows), consistent with DLBCL. Lymphomas from IµHABcl6 Ung^−/− mice have expanded follicles composed of small monotypic lymphocytes that are predominantly PNA⁻, consistent with FL. Pre-B-cell lymphomas, shown here from IµHABcl6 Msh2^−/− mice, are composed of medium-sized monotypic PNA⁻ lymphocytes. Images were obtained on a Zeiss Axio Imager A1 microscope. Short scale bars represent 500 µM, and long scale bars represent 50 µM.