A large proportion of aged AKR strain mice develop spontaneous lymphomas as a result of viral transformation. Whereas most of these malignancies involve thymic T lymphocytes, B-cell and peripheral T-cell lymphomas have been observed (Greenberg et al. 1977, Zatz et al. 1981). During our studies of AKR tumorigenesis, an unusual lymphoma, AKR 225, was established in transplantation and characterized. The spontaneous primary tumor, which arose in an 11-month-old AKR male mouse, involved the spleen and peripheral lymph nodes, but not the thymus. Phenotypic analysis of spleen cells from the primary tumor demonstrated that the lymphoma expressed surface immunoglobulin (sIg) but not Thy-1. AKR 225 was transplanted into syngeneic recipients and further characterized by flow cytometry (FCM) analysis using a panel of monoclonal antibodies (MoAbs.) against murine differentiation antigens (Table 1). The reactivity of these antibodies on normal AKR splenocytes is presented for quantitative and qualitative comparison. More than 80% of the splenocytes from a mouse bearing the AKR 225 lymphoma reacted with MoAbs. against determinants associated with normal B lymphocytes, such as sIg (/~ heavy and โข light chains), I-A (Ia.2), I-E/C (Ia.7), E2, ThB, and the B-cellassociated DNL 1.9 antigen and B220 antigen, but did not react with antibodies against Thy-1 or T30 antigens (Table 2). A surprising finding was that this Thy-1 -, sIg รท lymphoma expressed both Ly-1 and Ly-2 antigens (Fig. 1). The specificity of the reaction of the Ly-2-specific antibody with this tumor was confirmed using alloantibodies. AKR 225 lymphoma cells bound monoclonal Ly-2.1-specific, but not Ly-2.2-specific antibody.
To address the question of whether these antigens were actually synthesized by the lymphoma cells, enzymatic stripping and regeneration experiments were undertaken. The Ly-1, Ly-2, and surface # heavy chains were totally removed from the cell surface by trypsin digestion by the method described previously (Lanier et al. 1981a; < 5% positive cells after treatment). After overnight culture, > 70% of cells reexpressed sIgM, as well as both Ly-1 and Ly-2 in the same quantity as the Table 1. Monoclonal antibodies L.L. Lanier et al.