Immunoarchitecture of the "pseudofollicles" of well-differentiated (small) lymphocytic lymphoma: a comparison with true follicles.

Some human malignant lymphomas of the B-cell type have morphologic and immunologic similarities to follicles seen in nonneoplastic reactive lymph nodes. In contrast, a peculiar, vaguely nodular pattern of growth called "pseudonodules" or "pseudofollicular proliferation centers," which is morphologically distinguishable from "true" follicles, is seen in malignant lymphoma, well-differentiated (small) lymphocytic type (WDL). To characterize the cellular components of "pseudofollicles," we undertook a detailed, comparative immunohistologic study of the architectural relationship and distribution of T cells, B cells, and follicular dendritic reticulum cells (DRCs) in reactive follicles, neoplastic follicles, and pseudofollicles. We report several observations on the presence of DRCs and T-cell subset topography in pseudofollicles. Immunohistologic staining for the C3d complement receptor on DRCs revealed that DRC networks associated with "true" follicles were present in all cases of reactive follicular hyperplasia (RFH) and malignant lymphoma, nodular, poorly differentiated lymphocytic type (PDL) studied. Surprisingly, DRC networks were also identified in 8 of 23 cases of WDL. Although the size distribution of DRC network diameters was nearly identical in RFH and PDL, the sizes were markedly diminished in WDL. Immunohistologic staining for Leu 3+ and Leu 2+ T-cell subsets confirmed cellular arrangements in RFH and PDL reported by others. In only 2 of 23 cases of WDL could T cells localized to "pseudofollicles" in frozen tissue sections be identified in a nonrandom arrangement.