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Primary central nervous system lymphoma (PCNSL) is a rare disease, especially among non-AIDS patients. Although almost all PCNSLs belong to the diffuse large B-cell lymphoma (DLBL) category, its clinical course differs from that of other types of DLBL. To elucidate the histogenesis of PCNSL, we analyzed the source of the cells from its variable region (VH) sequences using the polymerase chain reaction (PCR) method to amplify the immunoglobulin heavy chain (IgH) gene of DNA extracted from paraffin sections. Fifteen patients with AIDS-unrelated PCNSL of DLBL type, (7 males and 8 females), were evaluated. Only one case showed positive evidence of EBV infection. The prognosis was very poor with a median survival of 9 months. Analysis of the VH sequences revealed that the VH4 family was used in 4 cases and the VH3 family in 2 cases. The homology with previously published germline sequences was random, ranging from 82.7-93.2%, showing intermediate to high somatic mutations. In 3 of 6 cases, the existence of intraclonal diversity was suspected. These findings suggest that PCNSLs are histogenetically derived from antigen selected B cells in the germinal center (GC) environment.

We have analyzed the immunoglobulin heavy chain (VH) gene variable regions (CDR2 and FW3) of 101 Japanese cases with peripheral B cell neoplasms. When all except one case with a deletion were graphed by frequency of replacement mutation, the 100 cases could be separated into two groups: 24 cases with zero, one and two mutations (germline or low frequency of somatic mutation); and 76 cases with three or more mutations (medium to high frequency of somatic mutation). While most mantle cell lymphoma cases (11/13) showed germline or low frequency of somatic mutation, all cases of mucosa-associated lymphoid tissue (MALT) lymphoma (11/11), follicular lymphoma (three of three cases), plasma cell myeloma (seven of seven cases) and most cases of diffuse large B cell lymphoma (DLBCL; 42/47) belonged to the latter group. These 76 cases, therefore, may be considered to show somatic hypermutation. More than half of chronic lymphocytic leukemia/small lymphocytic lymphoma cases (CLL/SLL; eight of 13) showed a hypermutated VH gene and the ratio of replacement mutation: silent mutation in CDR2 of CLL/SLL was considerably higher compared with DLBCL and MALT lymphoma, showing somatic hypermutation. When comparing VH gene type of B cell-CLL (B-CLL) among our series and those in the literature, more cases of CD5+ B-CLL in the Western literature have the VH5 and VH6 family types, while more cases in Japan are reported to have VH4 family. The occurrence of VH families in B-CLL between Japanese and Western people seems to be comparable.

A hairy-cell leukaemia (HCL) cell line, HCL-O, was established from the peripheral blood of a 62-year-old Japanese patient with a unique variant of HCL strongly expressing CD21, the receptor for the Epstein-Barr virus (EBV). The HCL-O cells expressed antigens similar and dissimilar to those expressed with the original hairy cells. The HCL-O cells were more mature than the original cells in their degree of B-cell differentiation, as indicated by a decrease of CD19 and surface immunoglobulin (sIg) expression together with the appearance of CD38 and cytoplasmic Ig (cIg). In addition, the cells expressed CD11c recognized by Leu-M5, a monoclonal antibody usually positive for HCL. Their karyotype and Ig gene rearrangement pattern were identical to those of the original cells. The EBV genome was detected in the HCL-O cells but not in the original cells. The HCL-O cells spontaneously produced a large quantity of interleukin-6 (IL-6) in the conditioned medium, whereas IL-6 serum level was not so high. These findings indicate that the HCL-O cell line is derived from the leukaemic hairy cells and possibly, in vitro EBV infection took place easily in the original hairy cells through their CD21, resulting in subsequent immortalization. IL-6 production by HCL-O cells may be induced or enhanced by EBV, and the secreted IL-6 might play a role in their own growth or differentiation.