Detection and characterization of human high molecular weight B cell growth factor receptors on leukemic B cells in chronic lymphocytic leukemia

Development of a murine model for blastoid variant mantle-cell lymphoma

Blastoid-variant mantle-cell lymphoma (MCL-BV), unlike most B-cell non-Hodgkin lymphomas (NHL-Bs), is refractory to conventional chemotherapy and associated with a very poor prognosis. Development of new therapies has been hampered by the lack of valid animal models. We have developed a novel murine model of MCL-BV by crossing interleukin 14alpha (IL-14alpha) transgenic mice with c-Myc transgenic mice (double transgenic [DTG]). IL-14alpha is a B-cell growth factor that is expressed in a number of high-grade lymphomas, including MCL-BV. Ninety-five percent of IL-14alpha transgenic mice develop CD5(+) large B-cell lymphomas by 18 months of age. Sixty percent of c-Myc transgenic mice develop pre-B-cell lymphomas by 12 months of age. Close to 100% of DTG mice develop an aggressive, rapidly fatal lymphoma at 3 to 4 months of age that is CD5(+), CD19(+), CD21(-), CD23(-), sIgM(+). The tumor is found in the blood, bone marrow, liver, spleen, lymph nodes, gastrointestinal tract, and lungs and rarely in the brain, similar to the involvement seen in human MCL-BV. Immunoglobulin gene rearrangements document the monoclonality of the tumor. Cyclin D1 is highly expressed in these tumors, as it is in MCL-BV. DTG represents a novel model for MCL-BV that should reveal important insights into the pathogenesis of the lymphoma and contribute to the development of new forms of therapy.

Current status of flow cytometry in cell and molecular biology

This review summarizes recent developments in flow cytometry (FC). It gives an overview of techniques currently available, in terms of apparatus and sample handling, a guide to evaluating applications, an overview of dyes and staining methods, an introduction to internet resources, and a broad listing of classic references and reviews in various fields of interest, as well as some recent interesting articles.

Identification of a cDNA for a human high-molecular-weight B-cell growth factor

Proliferation is necessary for many of the phenotypic changes that occur during B-cell maturation. Further differentiation of mature B cells into plasma cells or memory B cells requires additional rounds of proliferation. In this manuscript, we describe a cDNA for a human B-cell growth factor we call high-molecular-weight B-cell growth factor (HMW-BCGF). Purified HMW-BCGF has been shown to induce B-cell proliferation, inhibit immunoglobulin secretion, and selectively expand certain B-cell subpopulations. Studies using antibodies to HMW-BCGF and its receptor have suggested that HMW-BCGF, while produced by T cells and some malignant B cells, acts predominantly on normal and malignant B cells. The HMW-BCGF cDNA was identified by expression cloning using a monoclonal antibody and polyclonal antisera to HMW-BCGF. Protein produced from the cDNA induced B-cell proliferation, inhibited immunoglobulin secretion, and was recognized in immunoblots by anti-HMW-BCGF antibodies. The amino acid sequence of HMW-BCGF deduced from the cDNA predicts a secreted protein of 53 kDa with three potential N-linked glycosylation sites. The identification of this cDNA will allow further studies examining physiologic roles of this cytokine. We propose to call it interleukin 14.

Abnormal response to a human B cell growth factor in patients with common variable immunodeficiency (CVI)

Patients with common variable immunodeficiency (CVI) generally fail to produce antigen-specific IgG. We have identified a lymphokine called high molecular weight B cell growth factor (HMW BCGF) that expands an IgG-producing subpopulation of B cells. The B cells from 15 of 16 patients with CVI evaluated in this study failed to proliferate to HMW BCGF, although they proliferated normally to another BCGF, low molecular weight BCGF (LMW BCGF). Nevertheless, 11 patients had more than normal numbers of B cells expressing HMW BCGF receptors. The HMW BCGF receptors on the B cells of three patients with CVI studied were the same molecular weight as the normal HMW BCGF receptor. Examination of B cells from four patients with CVI for intracellular signals produced in normal B cells after stimulation with HMW BCGF revealed that B cells from patients with CVI failed to developed significant increases in cyclic adenosine monophosphate or phosphoinositides after HMW BCGF stimulation. However, cytoplasmic phosphoinositides in the B cells from all four patients with CVI were already increased above what is observed in normal B cells before stimulation with HMW BCGF (either freshly isolated or Staphylococcus aureus Cowan I-activated B cell). Thus, the failure of B cells from patients with CVI to respond to HMW BCGF may be related to their abnormal activation in vivo. Since HMW BCGF expands a subpopulation of memory B cells, the inability of CVI B cells to respond to HMW BCGF may contribute to their abnormal secondary responses to antigens.

Interleukin 7 receptor ligation stimulates tyrosine phosphorylation, inositol phospholipid turnover, and clonal proliferation of human B-cell precursors

Functional interleukin 7 (IL-7) receptors are expressed on the surface of multiphenotypic, biphenotypic, and immature B-lineage human lymphoid precursor cells with germ-line immunoglobulin heavy-chain genes but not on more mature B-lineage lymphoid cells with rearranged and/or expressed immunoglobulin heavy-chain genes. Thus, IL-7 may have an important regulatory role during the earliest stages of human B-cell ontogeny. The engagement of the surface IL-7 receptors on immature B-cell precursor cells with recombinant human IL-7 (rhIL-7) results in enhanced tyrosine phosphorylation of multiple phosphoproteins, stimulates inositol phospholipid turnover and DNA synthesis, and promotes their clonal proliferation. These effects are (i) specific for rhIL-7, since rhIL-3, rhIL-4, rhIL-5, rhIL-6, and recombinant human granulocyte colony-stimulating factor do not elicit similar activities on IL-7 receptor-positive human pro-B cells; and (ii) mediated by IL-7 receptors, since they are not observed in IL-7 receptor-negative B-lineage lymphoid cell populations. rhIL-7-induced tyrosine phosphorylation on the 35-, 53-, 55-, 62-, 69-, 76-, 94-, 150-, 170-, and 190-kDa substrates as well as rhIL-7-induced stimulation of inositol phospholipid turnover are abrogated by the tyrosine kinase inhibitor genistein. These results demonstrate that the IL-7 receptor on immature human B-cell precursor populations is intimately linked to a functional tyrosine kinase pathway and tyrosine phosphorylation is an important and perhaps mandatory step in the generation of the IL-7 receptor-linked transmembrane signal.

Induction of proliferation by high molecular weight B cell growth factor or low molecular weight B cell growth factor is associated with increases in intracellular calcium in different subpopulations of human B lymphocytes

The activation of resting B cells with anti-surface Ig is associated with transient increases in intracellular calcium. In the present study, we demonstrate that stimulation of B cells which have already been activated by Staphylococcus aureus Cowan I (Sac), with high molecular weight B cell growth factor (HMW-BCGF) or low molecular weight B cell growth factor (LMW-BCGF), but not IL-2, IL-4, or interferon-gamma, is associated with an increase in intracellular calcium, which is modest compared to that seen with anti-Ig (approximately 100 nM vs approximately 400 nM). The increases in intracellular calcium induced by HMW-BCGF or LMW-BCGF occur in distinct but overlapping subpopulations of B cells. Thus, increases in intracellular calcium in human B cells occur not only upon activation but also upon the induction of proliferation by certain (but not all) B cell growth factors. Presumably, the effect of increasing intracellular calcium during the induction of proliferation is to modify a different group of intracellular molecules than those induced during activation.

Expression of the fibronectin receptor VLA-5 is regulated during human B cell differentiation and activation

We examined the expression of VLA-5, a fibronectin receptor, during human B cell development and activation. VLA-5 is a member of the integrin supergene family; VLAs are heterodimers of at least six unique alpha chains sharing a common beta chain; most are involved in cell attachment to extracellular matrix (ECM). A hypothesis of haematopoietic development is that maturing cells leave the bone marrow because of the loss of VLA-5 during differentiation. However, mature B cells are not primarily circulating cells, and the role of ECM receptors in homing to peripheral lymphoid tissue and inflammatory sites is unknown. To examine the expression of VLA-5 during B cell development, cell lines blocked at specific stages of differentiation were evaluated for their synthesis and surface expression of VLA-5 using VLA-5-specific antibody and cDNA probes. VLA-5 mRNA and surface expression were found in the pre-B cell lines, REH and Nall 1, but not in more differentiated Raji cells or in several EBV-transformed peripheral B cell lines. Circulating peripheral B lymphocytes and resting tonsillar and splenic B lymphocytes expressed no VLA-5 by FACS analysis. Interestingly, mRNA and surface expression of VLA-5 were found in SKW, a highly differentiated, IgM-secreting line. In addition, low levels of staining for VLA-5 expression could be demonstrated when tonsillar or peripheral blood B lymphocytes were stimulated by Staphylococcus aureus Cowan (SAC). All cell lines expressed VLA-3 and VLA-4, two other receptors reported to mediate fibronectin binding in some cell types. Thus, our studies provided no evidence for developmental or inflammatory regulation of these receptors. Binding studies, however, demonstrated that adherence of both pre-B REH cells and SKW cells to fibronectin was almost completely inhibited by a monoclonal antibody to VLA-5 alpha. In addition, Raji cells, which lack VLA-5 but express VLA-3 and VLA-4, showed very low level binding to fibronectin. This demonstrates that for some B lymphocytes VLA-5, rather than other possible fibronectin receptors, primarily mediates attachment to fibronectin. These data also suggest that human VLA-5 expression is regulated during B cell development, with expression at a very early stage and then again after activation. This pattern of loss and reacquisition of an ECM receptor may be relevant to normal B cell maturation and to function during immunologic injury.