Expression of Pax5 gene in human haematopoietic cells and tissues: comparison with immunodeficient donors

In mice, Pax5 gene is indispensable for B cell development. Pax5-deficient mice fail to produce mature B cells owing to complete arrest of B cell development at a precursor stage. However, the lineage and stage of human Pax5 gene expression have remained elusive. In this investigation expression of the human Pax5 gene was studied. Pax5 gene expression was detected in B cell lines but not in myeloma cell lines. CD19 expression was correlated with Pax5 gene expression. Adult spleen and bone marrow and fetal spleen and liver showed strong Pax5 gene expression, as did the corresponding mouse tissues, as reported previously. In common variable immunodeficiency (CVID) peripheral blood lymphocytes (PBL) with a decreased number of B cells, no Pax5 gene expression was detected. Some CVID PBL stimulated with IL-2, IL-10 and anti-CD40 monoclonal antibody, expressed the Pax5 gene. Defect of Pax5 gene expression in CVID may be caused by regulatory T cell disorder.     

PAX5 promotes pre-B cell proliferation by regulating the expression of pre-B cell receptor and its downstream signaling

PAX5 is indispensable for the commitment of early lymphoid progenitors to the B cell lineage as well as for the development of B cells. Although previous studies have indicated that the Pax5-conditional-knockout mouse exhibited dedifferentiation of mature B cell and the development of aggressive lymphomas, the changes of Pax5 gene expressions in pre-B cells have not been analyzed. To understand the functional importance of Pax5 gene in the proliferation and survival of pre-B cells, we established a Pax5-knockdown model using 70Z/3 pre-B cell line. Pax5 knockdown 70Z/3 cells (70Z/3-KD cells) showed down-regulations of pre-BCR compounds such as CD19, BLNK, Id2 and λ5. The signaling via pre-BCRs was significantly diminished in the 70Z/3-KD cells, and this alteration was normalized by restored Pax5 gene expression. Loss of PAX5 reduced the growth rates in the 70Z/3-KD cells, compared to the mock cells. Meanwhile, the proliferation of pre-B cells was reduced by the knockdown of Pax5 gene. Moreover, further examinations showed that PAX5 was also activated in B cell acute lymphoblastic leukemia (B-ALL) as a cell proliferation enhancer. These findings suggested that pax5 is critically important for the proliferation and survival of pre-B cells.     

Lymphomas and lymphoproliferative diseases of the lung

Primary pulmonary lymphoma is a rare disease and the majority of cases represent extranodal marginal zone lymphoma, followed by diffuse large B-cell lymphoma. Other lymphomas that commonly involve the lung include lymphomatoid granulomatosis, a neoplasm of large EBV-positive B cells that are typically outnumbered by non-neoplastic T cells, and classical Hodgkin's lymphoma, which usually reflects systemic dissemination or direct mediastinal extension. The differential diagnosis of marginal zone lymphoma includes secondary involvement by other systemic low-grade B-cell lymphomas and chronic reactive conditions, such as nodular lymphoid hyperplasia, while the other entities elicit a differential diagnosis that includes various high-grade lymphoid neoplasms. A specific diagnosis can usually be achieved on the basis of histological evaluation and immunophenotyping, although molecular genetic studies may be required in certain situations. Such a multiparameter approach may be warranted to accurately diagnose these entities due to differing clinical implications in terms of prognosis and treatment.     

Frequent detection of Epstein–Barr virus-infected B cells in peripheral T-cell lymphomas

Although Epstein–Barr virus (EBV) positivity has been described in peripheral T-cell lymphomas (PTCLs) in Chinese patients, the cellular lineage of EBV-harbouring cells is unknown. Forty-four cases of PTCL were therefore studied by in situhybridization (ISH) for EBV-encoded small non-polyadenylated RNA 1 and 2 (EBER), and the lineage of the EBER+ cells was determined by double labelling. The findings were further correlated with the clonality of EBV and the genotype of these EBER+ tumours. The results for the detection of EBV by ISH show that 23 of the 44 cases were EBER+. In 5/23 of the EBER+ cases, EBER was found in around 50 per cent of atypical cells and in 18/23 cases, EBER was found in a subpopulation of atypical cells. Amongst the EBER+ cases, all 15 tested showed clonal T-cell receptor gene rearrangement by Southern blot hybridization. Double labelling was successfully done in 11 EBER+ cases, and by comparison, EBER+/CD20+ B cells outnumbered the EBER+/CD3+ T cells in all these cases. EBV clonality analysis revealed that EBV was monoclonal in six EBER+ cases and biclonal in three cases. With the predominance of EBV+ B cells over EBV+ neoplastic T cells being observed in most of these cases, it is possible that the EBV-infected clonal population may be of B-cell lineage. This was supported in some cases where a faint clonal band was seen over a background smear in the gene rearrangement study of immunoglobulin heavy chain gene by polymerase chain reaction (PCR), indicating a minor B-cell clone. It is concluded that in EBV+ PTCL, EBV is preferentially localized in B cells rather than neoplastic T cells. The neoplastic T cells may support the clonal proliferation of a subpopulation of EBV+ B cells in PTCLs. © 1998 John Wiley & Sons, Ltd.     

PRDM1/Blimp-1 is expressed in human B-lymphocytes committed to the plasma cell lineage

PRDM1/Blimp-1 (in human and mouse, respectively) has a central role in determining and shaping the secretory arm of mature B-cell differentiation. In this study, a mouse monoclonal antibody that recognizes PRDM1 was used to detail its distribution in normal human lymphoid tissue and in lymphoid neoplasms that correspond to different stages of B-cell differentiation. PRDM1 was expressed in germinal centre blasts that co-express Pax5, CD19, CD20, and CD10, but not BCL6 or MTA-3. Pax5 was downregulated and full plasma cell morphology and phenotype were acquired by PRDM1+, nuclear cREL-, pre-plasma cells upon exit from the germinal centre. Activated extrafollicular B-cells (CD30+, Pax5+) were largely PRDM1-. PRDM1 was also absent in tissue histiocytes and the majority of resting T-cells and S-100+ antigen-presenting cells. PRDM1 and CD138 were expressed simultaneously in human lymphomas with plasma cell differentiation, but not in marginal zone lymphomas or chronic lymphocytic leukaemias. A minority of diffuse large B-cell lymphomas expressed PRDM1 and Hodgkin lymphomas were largely PRDM1-. Infiltrating T-cells in PRDM1- B-cell lymphomas expressed PRDM1. In conclusion, PRDM1 staining is a reliable and informative assay to define plasma cell commitment and differentiation in human normal and neoplastic B-cell lineages.     

The role of gene rearrangements for antigen receptors in the diagnosis of lymphoma obtained by fine-needle aspiration. A study of 63 cases with concomitant immunophenotyping

To assess the efficacy of performing genotyping in addition to immunophenotyping as an adjunct to cytologic diagnosis, 63 consecutive patients with fine-needle aspirates of lymphoproliferative lesions who had concurrent immunophenotyping and genotyping performed on fine-needle aspirate cell suspensions were studied. Thirty-nine of 63 specimens (62%) that appeared to contain non-Hodgkin's lymphoma and that proved to be of B-cell lineage by genotyping were accurately phenotyped and shown to be monotypic for immunoglobulin light chains by cell suspension immunocytochemistry. Genotyping facilitated lineage assignment and/or confirmed clonality in 17 of 63 specimens (27%) that were difficult to determine based on morphologic data. These include cases of atypical lymphoid proliferations with polyclonal or inconclusive markers (n = 6), peripheral T-cell lymphoma (n = 3), extracutaneous mycosis fungoides (n = 1), lymphoblastic lymphoma (n = 4), null cell lymphoma (n = 1), and specimens with equivocal or technically unsatisfactory markers (n = 2). Based on these results, it is proposed that genotyping for lineage assignment and/or clonality be performed to include cases of atypical lymphoid proliferations, T-cell malignant neoplasms, lymphoid malignant neoplasms with equivocal markers, and differentiation of lymphoid from nonlymphoid neoplasms. Genotyping by antigen-receptor gene rearrangement appears to be redundant in cases with mature B-cell phenotypes that demonstrate monoclonality by immunophenotyping.