Richter's syndrome. Evidence for the clonal origin of the two proliferations

A case of Richter's syndrome was investigated by several technics: light and electron microscopy, surface markers, immunohistological studies and immunoelectron microscopy. On light microscopy lymph node proliferation was composed of large lymphoid cells, some exhibiting Reed-Sternberg like features. On electron microscopy many intermediary cells, from small lymphocytes to immunoblasts and plasma cells, were noted. The circulating small lymphocytes were characterized as B cells (SIg +; MRBC+). The lymph node cells shared the same SIg phenotype (IgMK) but the percentage of MRBC was slightly lower. Immunohistological studies showed that lymph node cells were stained exclusively by anti micron and anti kappa antisera. These results are indicative of the B clonal origin of the two cell proliferations. Immunoelectron microscopy showed three staining patterns: 1) cells presenting only surface staining, 2) cells with diffuse staining presumably related to ribosomal fixation, 3) cells with endoplasmic reticulum staining. The significance of these three patterns is discussed with regard to B lymphocyte differentiation.