Intermediate lymphocytic lymphoma: an immunohistologic study with comparison to other lymphocytic lymphomas.

In an immunohistologic analysis of 13 cases of intermediate lymphocytic lymphoma (ILL), the immunophenotype of ILL was compared to the immunophenotypes of other B-lymphocytic lymphomas and the normal lymphoid follicle to determine the normal cell in the scheme of B-cell differentiation that corresponds to ILL. The characteristic immunophenotype of ILL was surface IgM +/- D+, cytoplasmic immunoglobulin -, B1+, BA1+, B2-, BA2-, B4+, Leu 14+, HLA-DR+, Leu 1+, and common acute lymphoblastic leukemia associated (CALLA) antigen -. The immunophenotype of ILL was similar to that of lymphocytes in normal primary follicles and the mantle zones of secondary follicles. The "immature" phenotype of ILL was identical to that of small lymphocytic lymphoma, which strongly supports their close lineage relationship. In contrast, the "mature" phenotypes of the follicular center cell and lymphoplasmacytoid lymphomas suggest that they correspond to normal cells at later stages of differentiation. Our findings indicate that B-lymphocytic lymphomas recapitulate the normal stages of B-cell differentiation. The cell of ILL appears to be an immature B cell that homes to, and resides in, primary follicles and the mantle zones of secondary follicles. The cytologic, architectural, immunologic, and clinical features of ILL indicate that it should be included as a separate category in the International Working Formulation.