Analysis of the immunoglobulin heavy chain gene variable region of intravascular large B-cell lymphoma

Intravascular large B-cell lymphoma (IVLBL) is a rare neoplasm characterized by proliferation of lymphoma cells within the blood vessels. The cell origin of IVLBL has not yet been determined. We examined cell lineage, with immunohistochemical staining and molecular analysis, using polymerase chain reaction (PCR) of the variable region of the immunoglobulin heavy chain (Ig-VH) gene. We also investigated the cell origin using direct sequence analysis of the complementary-determining region 2 (CDR2) and framework region 3 (FR3) in six cases, consisting of two male and four female patients. The sequences in five cases showed frequent mutations. The percent homology to their closest germline genes ranged from 74.7 to 91.8%. However, one case showed a percent homology of 99.4% in CDR2 and FR3 of Ig-VH. All cases showed rearrangements of VH3 family genes. Interestingly, three of the IVLBL cases with hypermutated IgH genes showed the expression of CD5. Therefore, expression of CD5 in lymphoma cells does not indicate that the origin of IVLBL is the same as mantle cell lymphoma having the character of CD5 expression, which develops in pre-germinal center cells. Our results indicate that most IVLBLs may originate in the post-germinal center cells, based on the presence of somatic mutation in VH genes, although some heterogeneous cases are intermingled within IVLBL.