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Biomedical subjects

F Melchers

Publications and source records attributed to F Melchers.

At least 19 recordsLinked to original sources
PubMed1992

Development of autoimmune disease in SCID mice populated with long-term "in vitro" proliferating (NZB x NZW)F1 pre-B cells.

Pre-B cell lines proliferating for several months on stromal cells in the presence of interleukin 7 (IL-7) were established from fetal liver of (NZB x NZW)F1 mice. They express the B lineage-specific markers PB76, B220, and VpreB, but do not express surface immunoglobulin (sIg). Upon removal of IL-7 from the culture, they differentiate to sIg+ B cells that can then be stimulated by lipopolysaccharide to become IgM-secreting cells. Transfer of these pre-B cell lines into SCID mice leads to hypergammaglobulinemia of IgM (600-900 micrograms/ml), IgG2a (1-3 mg/ml), and IgG3 (300-500 micrograms/ml) for the next 3-5 mo. The spleen appears populated with (NZB x NZW)F1-derived pre-B cells, few B cells, and many IgM and/or IgG-producing plasma cells. In contrast, SCID mice populated with pre-B cell lines of normal (C57BL/6 x DBA/2)F1 mouse fetal liver develop normal levels of serum IgM (approximately 100-300 micrograms/ml), almost no detectable levels of IgG, and no plasma cell hyperplasia. The (NZB x NZW)F1 pre-B cell-populated SCID mice contain elevated serum titers of IgG antinuclear autoantibodies, but no retroviral gp70-specific nor erythrocyte-specific autoantibodies. Up to 20% of the SCID mice develop proteinuria as a consequence of IgG deposits in the kidney glomeruli during a 7-mo period of observation. All signs of autoimmune disease seen in these mice are independent of the sex of the SCID host. This experimental system provides a distinction between the disease-determining (NZB x NZW)F1 genes, which are expressed in the B lymphocyte lineage and cause the development of the disease, from those expressed in other cell lineages which only modulate its progression.

Animals↗
PubMed1992

A critical role of lambda 5 protein in B cell development.

The lambda 5 gene is a homolog of immunoglobulin J lambda-C lambda genes, expressed specifically in immature B-lineage cells. Lambda 5-encoded molecules form membrane complexes with mu or D mu proteins in association with an additional protein specifically expressed in immature B cells that is encoded by the Vpre-B gene. We have generated mice in which the lambda 5 gene is inactivated by targeted gene disruption in embryonic stem cells. In these mice, B cell development in the bone marrow is blocked at the pre-B cell stage. However, the blockade is leaky, allowing B cells to populate the peripheral immune system at a low rate. These cells are allelically excluded and able to respond to antigen.

Animals↗
PubMed1992

A novel regulatory myosin light chain gene distinguishes pre-B cell subsets and is IL-7 inducible.

We describe a novel regulatory myosin light chain gene (termed precursor lymphocyte-specific regulatory light chain or PLRLC) that is expressed specifically in precursor B and T lymphocytes. PLRLC is the first example of a regulatory myosin light chain gene which displays specific expression in non-muscle cells. PLRLC is expressed in adult bone marrow derived normal and transformed pre-B cells; in the former, PLRLC expression levels are induced by the pre-B cell specific growth factor interleukin-7 (IL-7). PLRLC is not expressed in either transformed pre-B cells derived from fetal liver or in normal fetal liver pre-B clones grown in the presence of IL-7. Therefore this gene provides the first marker that clearly distinguishes these two pre-B subsets. Finally, several of the different PLRLC transcripts potentially encode regulatory myosin light chains with unique structural features. The unique distribution, regulation and structural features of the PLRLC gene products suggest an important role for PLRLC during lymphocyte development.

Amino Acid Sequence↗
PubMed1992

The expression of the mouse VpreB/lambda 5 locus in transformed cell lines and tumors of the B lineage differentiation pathway.

The expression of RNA transcripts from two pre B lymphocyte related genes, VpreB and lambda 5, has been studied in a series of transformed cell lines which appear frozen at different states of B lineage differentiation, from early progenitors to surface Ig positive B cells. In the HAFTL-1 cell line, which arose from fetal liver by transformation with a retrovirus containing the Hras oncogene, Northern analysis of poly A+ mRNA as well as in situ hybridization of RNA in single cells revealed that lambda 5 and VpreB are already expressed at the progenitor stage and increase in expression as the progenitors differentiate to precursor (preB) cells, or are turned off as the progenitors differentiate to myeloid cells. Continued rearrangements of Ig genes in pre B cell lines leading to Ig expression on the surface of NFS-5 pre B cells do not influence the continued expression of VpreB and lambda 5. Surface Ig-positive B lineage cell lines also express the pre B-related genes. Both Ly1+ as well as Ly1- pre B cells are VpreB- and lambda 5-positive. Lipopolysaccharide (LPS) stimulation of 70Z/3 pre B cells does not turn off lambda 5 expression. It therefore appears that, at least in transformed cell lines, the expression of VpreB and lambda 5 is not directly regulated by the expression of microH, kappa L, or lambda L chains, LPS reactivity, or the Ly1 surface antigen. Fusion of plasmacytoma cells with normal pre B cells to generate pre B hybridomas leads to down-regulation of VpreB/lambda 5 expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

VpreB gene expression in hematopoietic malignancies: a lineage- and stage-restricted marker for B-cell precursor leukemias.

We show here that analysis of VpreB gene transcription can be a specific way to identify acute leukemias of cells at very early stages of B-cell development. Northern blot analysis of RNAs from 63 leukemia samples showed that VpreB RNA was present in malignancies of precursor B cells, the expression being a feature of both common acute lymphoblastic leukemia (ALL) (CD10+) and null ALL (CD10-). It was absent from malignancies of mature B cells (surface Ig positive), from acute leukemias of the T-cell lineage and granulocyte-macrophage lineages, and from normal tonsil B and T lymphocytes. Chronic myeloid leukemia blast crises of the B-precursor-cell type expressed the VpreB gene while myeloid blast crises did not. VpreB RNA was also expressed in the neoplastic cells of one of three patients with acute undifferentiated leukemias. These data show that VpreB RNA expression is a marker of the malignant forms of precursor B cells, and that it appears at least as early as cytoplasmic CD22 and CD19 in tumors of the B-cell lineage.

Blotting, Northern↗
PubMed1991

The c-kit-encoded tyrosine kinase regulates the proliferation of early pre-B cells.

A monoclonal antibody (mAb; ACK2) recognizing the extracellular domains of the c-kit-encoded tyrosine kinase has been employed to demonstrate that c-kit is involved in B lymphocyte development. The c-kit-encoded tyrosine kinase is expressed on the surface of normal DHJH-rearranged murine pre-B cell clones which proliferate continuously at that stage in vitro on stromal cells and in the presence of recombinant interleukin 7. These pre-B cell clones, capable of differentiation to surface immunoglobulin-positive B cells in vitro and in vivo, are inhibited by the mAb in their proliferation while remaining capable of differentiation to surface immunoglobulin-positive B cells. Stimulation of mature B cells by mitogens is unimpaired by the mAb. This indicates that c-kit regulates early antigen-independent, but not late antigen-dependent, B cell development.

Animals↗
PubMed1991

The kappa/lambda ratio in surface immunoglobulin molecules on B lymphocytes differentiating from DHJH-rearranged murine pre-B cell clones in vitro.

The expression of kappa and lambda light chains in surface immunoglobulin (sIg) molecules on B lymphocytes differentiating from murine pre-B cell clones in vitro was analyzed. The four pre-B cell clones used represent a very early pre-B cell stage. They have their heavy chain loci DJ rearranged and their light chain loci in germ-line configuration. In order to grow in vitro, these clones require contact with stromal cells and the stimulatory activity of interleukin (IL) 7. Upon removal of IL 7 from the cultures, these clones differentiate within 3 days into sIg+ B cells. Between 7% and 12% of IgM+ B cells could be detected in these cultures. The majority (78%-92%) of the IgM+ B cells co-expressed kappa light chains. The percentage of lambda light chain expressing B cells was below detectable level. Upon lipopolysaccharide (LPS) stimulation, the percentages of IgM+ B cells increased dramatically (from 32%-64%). The majority (91%-97%) of the IgM+ B cells express kappa chains, but a very small percentage (3.1%-5.0%) express lambda. A similarly high kappa/lambda ratio was found in 418 hybridomas prepared from these LPS-stimulated B cells (388 kappa+ and 30 lambda+). Thus, the high kappa/lambda ratio characteristic of the mouse peripheral B cell repertoire is already evident in the antigen-independent transition from pre-B to B cells.

Animals↗
PubMed1991

Long-term proliferating early pre B cell lines and clones with the potential to develop to surface Ig-positive, mitogen reactive B cells in vitro and in vivo.

Cell lines and clones were established from PB76-positive mouse fetal liver at day 13 and 14 of gestation, which proliferated with division times of a day in serum-substituted cultures under the stimulatory influence of adherent stromal cells and the cytokine IL-7 for periods longer than half a year. These lines expressed varying levels of the B lymphocyte lineage related markers PB76, B220, BP-1, VpreB and lambda 5, but no surface Ig or MHC class II molecules. All clones expressed PB76, VpreB and lambda 5 in a high percentage of cells, while B220 and/or BP-1 expression was low or undetectable in some. A cell line, and several clones established from it, all had kappa and lambda light chain genes in germ-line configuration. Either one or both of their H-chain-gene containing chromosomes carried a DH to JH. These pre B cell lines and clones could be induced to VH to DH and VL to JL rearrangements. This resulted in the development of varying percentages of sIg-positive surface, MHC class II negative, LPS-reactive B cells within 2-3 days, in the absence of contacts with stromal cells and/or IL-7. When injected into SCID mice, the cultured pre B cells populated the spleen of these mice to 5% with surface Ig-, MHC class II-positive LPS-reactive cells for greater than 25 weeks. The long-term in vitro proliferative capacity of these DH-JH rearranged pre B cell clones makes them major candidates for committed stem cells of the B lineage.

Animals↗
PubMed1990

The proteins encoded by the VpreB and lambda 5 pre-B cell-specific genes can associate with each other and with mu heavy chain.

The murine pre-B cell-specific genes VpreB and lambda 5, as well as the murine gene for mu heavy chain, were introduced into Ltk- fibroblast cells which normally do not express these genes. Stable transfectants carrying these genes produced the corresponding proteins of 15.5, 21.5, and 75 kD. They secreted the three proteins as a triple complex that could be immunoprecipitated by mu heavy chain-specific antibodies, consisting of one VpreB, one lambda 5, and one mu heavy chain. The mu heavy chain and lambda 5 were disulfide-bonded with each other, while the VpreB protein was noncovalently associated. These experiments proved that the VpreB, lambda 5 and mu H chain proteins can form a heavy/light chain-like heterocomplex.

Animals↗