Age-related changes in the morphology and immunophenotype of spontaneous lymphomas of SJL/N mice

Forty-four SJL mice were killed at intervals to follow the spontaneous development of lymphomas. These were detected in 28 of 38 mice aged 24 weeks or more. Immunoperoxidase stains were applied on cryostat sections of lymphomas from various sites (spleen, mesenteric lymph nodes, Peyer's patches, and other lymph nodes), sampled from 19 mice of different age groups, to study tumour immunophenotype in correlation with histological features. With a panel of antibodies against Thy 1.2, Lyt 1, and Lyt 2, and the mouse immunoglobulin heavy and light chains, all the 19 tumours were shown to be B-cell derived. This was further supported by the detection of Ia antigens on the tumour cells. Six mice had plasmacytoid or predominantly plasmacytoid tumours expressing gamma kappa. Three mice had mixed plasmacytoid and pleomorphic tumours which also showed gamma kappa positivity. The ages of these nine mice ranged from 24 to 44 weeks with a median of 36 weeks. Pleomorphic tumours were found in ten mice (age range = 36-52 weeks, median = 44 weeks). These tumours were more heterogeneous, expressing either alpha, mu, or gamma, or with loss of heavy chain expression altogether. These age-related changes are probably a sign of progressive loss of differentiation in B lymphomas.