| Abstract: | The relation between chronic lymphocytic leukemia (CLL, lymphocytic lymphoma (SL), plasmacytoid lymphocytic lymphoma (LP), plasmacytoma (PL), and multiple myeloma (MM) was investigated with cryostat sections stained with antibodies to immunoglobulin heavy and light chains and the B-cell differentiation antigens B1, B2, Ia, T1, and CALLA. Neoplasms were subclassified according to plasmacytoid features, leukemia (CLL) site of involvement (nodal or extranodal), serum monoclonal immunoglobulin, or clinical evidence of MM. The results defined two groups of lymphocytic lymphomas without plasmacytoid features (16 cases). Ten of these lymphomas were associated with CLL. Nine involved lymph nodes, all expressed IgM, five expressed IgD, nine were B2-positive, eight were T1-positive, and all were B1- and Ia-positive. Six of the lymphomas were not associated with CLL. Five of these tumors were extranodal, all were T1- B1+ B2- Ia+, five expressed IgM without IgD, and one contained IgG. These differences in clinical and immunologic phenotypes suggest that CLL and SL without CLL may be related to different stages of B-cell differentiation. T1 appeared to be a marker for CLL, since all T1-positive neoplasms were leukemic. Lymphomas with plasmacytoid features (ten cases) were more often extranodal, and none was leukemic. The immunologic phenotypes were heterogeneous: all of these lymphomas were T1-negative, most were IgM+ IgD-, three were B2-positive, and all were Ia-positive. The plasma cells in five lymphomas with marked plasmacytoid features were B1-negative; they were Ia-positive in four and Ia-negative in one. These data suggest that LP is a heterogeneous group, reflecting B cells at diverse stages of differentiation. Ten plasmacytomas, nine of which were associated with MM, differed from LP in showing heavy chain class switching; all were T1- B1- B2-, and all but one were Ia-negative. These results are consistent with the existence of two pathways or stages of B-cell differentiation: one that generates IgM-producing plasma cells, as seen in the primary immune response or in response to pokeweed mitogen, and one that generates IgG- or IgA-positive plasma cells, as seen in the late primary or secondary immune response. Plasmacytoid lymphocytic lymphoma reflects the first, while PL/MM reflects the second pathway. B1 appears to be lost before Ia in terminal plasma cell differentiation. |
