Expression of Activation-Induced Cytidine Deaminase and Transcripts of Immunoglobulin Variable Heavy Chains in Mature B-Cell Lines Lacking Immunoglobulin Protein Expression.

Expression of immunoglobulin (Ig) chains is a definitive marker of B-cell origin. Ig chains are generated during B-cell maturation by somatic rearrangement of Ig gene sequences. This rearrangement generally follows an orderly progression beginning with the heavy (H) chain genes and proceeding to the light (L) chain genes. The fact that Ig expression in B-cells generally reveals single L and H chains implies monoclonal cell expansion. Nevertheless, several exceptions have been reported, including double light chain positive cases. However, only little is known about mature B-cell malignancies lacking any Ig protein expression at all. In order to clarify the mechanisms of lacking any Ig protein expression in mature B-cell malignancies, we have analyzed the expression of activation-induced cytidine deaminase (AID), terminal deoxynucleotidyl transferase (TdT), recombination acting gene (RAG)-1 and RAG-2, transcription factors (TFs) and mRNA transcripts of Ig variable heavy (IgVH) chains using five both surface membrane (Sm) and cytoplasmic (Cy) Ig negative B-cell lines derived from acute lymphoblastic leukemia L3 type (ALL-L3), Burkitt’s lymphoma (BL) and pyothorax-associated lymphoma (PAL). BALM-9N and BALM-16 are ALL-L3, KATATA is BL, OPL-1 and OPL-3 are PAL-derived cell lines (EBV+). In cytogenetic analysis, t(8;14)(q24;q32) in BALM-9N and KATATA and t(8;22)(q24;q11) in BALM-16 were detected, respectively. Band 14q32 was not involved in the PAL cell lines. All cell lines showed rearrangement of IgH chain genes. Expression of RAG-1 and RAG-2 was variable, TdT was negative for all, AID was expressed in all cell lines except for PAL cell line OPL-3. The seven TFs BOB1/OBF1, E2A, IKAROS, OCT1, OCT2, PAX5 and PU1 were universally expressed at the mRNA level in all cell lines. Reverse transcriptase polymerase chain reaction elucidated the IgVH gene usage. BALM-9N = VH4; BALM-16 = VH2; KATATA = VH3; OPL-1 = VH3; OPL-3 = VH3. In summary, the present study demonstrates that Ig gene recombination, class switch recombination and somatic hypermutation machineries are not the cause for the lacking expression of both Sm/Cy Ig chains in mature B-cell malignancies. The lack of any Sm/Cy Ig expression in such mature B-cells may indicate rather a germinal center origin.