Pheno- and genotypic features of Epstein-Barr virus associated B-cell lymphoproliferations in peripheral T-cell lymphomas.

Among the 300 peripheral T-cell lymphomas (PTCL) searched for EBV positive non-resting B-cells by EBER in situ hybridization 12 have been identified with various forms of EBV-driven B-cell proliferation. This could be categorized into three major forms. i. In the first form scattered immature, mononuclear B-cells of immuno-, centroblastic type with CD20+. CD30+ CD45+, LMP1+ phenotype, reactive appearance and polyclonal immunoglobulin heavy chains gene rearrangement (IgH-R) were admixed to the PTCL cells. ii. The second form mimicked diffuse large B-cell lymphoma as homogenous sheets, largely demarcated from the PTCL, of mononuclear, immature B-cell of CD20+, CD30+, CD45+, LMP1+, EBNA-2+ phenotype but with lack of monoclonal IgH-R were present. iii. In the third form scattered Hodgkin-Reed-Sternberg (HRS) type of cells were noticed which exhibited the CD15+/-, CD20-/+, CD30+, CD45-, LMP1+, EBNA-2- phenotype and in 50% showed clonal IgH gene rearrangement in whole tissue DNA extract. The IgH associated transcription factors' (OCT2, BOB.1/OBF.1, PU.1) expression patterns in these cells corresponded to those of HRS cells in cHL. Based on analysis of 65 PTCLs, we have identified in the positive cases a highly significant increase of EBV+ small, reactive, resting B-cell compartment (75.9 / 100 HPF in PTCL vs. 1.5 / 100 HPF in control lymph nodes) likely to be due to the decreased immune surveillance. This progressive accumulation of EBV+ by-stander B-cell population in PTCLs might be the source of various B-cell proliferations, which in any form represent major diagnostic pitfalls and require a careful differential diagnostic procedure.