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A Cumano

Publications and source records attributed to A Cumano.

17 recordsLinked to original sources
PubMed1992

Bipotential precursors of B cells and macrophages in murine fetal liver.

LYMPHOCYTES (B and T cells) derive continuously from the same multipotential stem cells that produce myeloid cells, including erythrocytes, granulocytes and macrophages. Tri- and bipotential myeloid intermediates between the multipotential stem cells and later unipotential cells have been identified using clonal methods in culture. Although similar methods have detected committed pre-B cells in mouse fetal liver, earlier progenitors with additional non-B lineage options have not been demonstrated in normal tissues. We report the characterization and purification of fetal liver cells that generate clones containing both macrophages and B cells, identified biochemically and morphologically. The common origin of the two cell types was shown by culture of single precursor cells. Their dual potential and unrearranged immunoglobulin loci place the precursors before exclusive B-lineage commitment in the haematopoietic hierarchy. The availability of such cells in purified form will allow direct study of lineage choice in cells having both lymphoid and non-lymphoid options.

Animals↗
PubMed1992

The stromal cell line S17 supports the growth of lipopolysaccharide-stimulated CBA/N spleen cell colonies in vitro.

The expression of an X-linked defect in the CBA/N strain of mice has been found to result in a number of immune abnormalities. These include low responsiveness to antigens and a greatly reduced ability to respond to many of the common B cell mitogens. An in vitro manifestation of this condition is the virtual inability of CBA/N B cells to form colonies in lipopolysaccharide (LPS)-containing semisolid agar cultures. In this report we show evidence that the colony-forming ability of CBA/N spleen cells can be effectively restored by the bone marrow stromal-derived cell line S17. Spleen cells from 4-5-week-old homozygous CBA/N female mice were grown in double-layer agar cultures containing S17 feeder layers. Control cultures contained the fibroblast-like cell line 95.17 or were treated with medium alone. It was found that at an input cell concentration of 10(4) cells per plate, CBA/N colony formation was increased from a frequency of approximately 1 in 5,000 to 1 in 50 total splenic cells. Studies with purified surface immunoglobulin-positive cells indicate the direct involvement of S17 in this process. The CBA/N colonies formed were dependent on the presence of a mitogen (LPS) and secreted detectable amounts of IgM. Major implications of these findings and the application of this assay system to study the CBA/N defect have been discussed.

Animals↗
PubMed1992

Enrichment and characterization of uncommitted B-cell precursors from fetal liver at day 12 of gestation.

We describe an assay system that allows precursor cells, uncommitted for heavy and light chain immunoglobulin expression, to develop into B lymphocytes that can differentiate to antibody-producing cells. Some precursors have the immunoglobulin loci in germ-line configuration. Approximately 200-1500 precursor cells are present in one fetal liver by day 12 of gestation; they express the surface marker AA4.1. Most precursors do not express the B220 marker. Commitment to heavy chain immunoglobulin expression occurs after an average of two cell division; commitment to light chain expression takes place after two additional rounds of division. DNA analysis from the progeny of single precursor cells shows that: (i) most B220- precursor cells have not completed D-J rearrangement (9/11) and some were in germ line configuration (4/11); and (ii) most B220+ precursor cells exhibit two D-J rearrangements (4/5 samples). These experiments define two types of B-lymphocyte precursor cells in fetal liver: the first, B220+ AA4.1+, acquires the capacity to respond to mitogens only after 5 days in culture, and does not have productive V-D-J rearrangements but might exhibit two stable D-J rearrangements; the second, B220- AA4.1+, acquires the capacity to respond to mitogens only after 9 days in culture and can be in germ-line configuration in the Ig loci, and undergoes rearrangement of heavy and light chain genes in vitro. Both precursor types require interaction with stromal cells before becoming responsive to interleukin 7.

Animals↗
PubMed1991

Expansion of myelopoietic precursors and inhibition of B-cell precursors in mice that express a T-cell receptor gamma (V gamma 1.1J gamma 4C gamma 4) transgene.

Knowledge of the genetic determinants that can affect renewal of multipotential stem cells and their commitment to specific cell lineages is essential to our understanding of multicellular development. However, despite the vast amount of accumulated knowledge in this area, genetic determinants that affect renewal and commitment of precursor cells are unknown. In this study, we demonstrate that three independently derived founder mouse strains, transgenic for the TcR V gamma 1.1J gamma 4C gamma 4 (TcR gamma 4) chain gene, differed significantly from normal mice in their development of T and B cells as well as myelopoietic precursor cells. Ontogenic programs consistent with an acceleration of T-cell development and a delayed appearance and suppressed levels of pre-B- and B-cell precursors were evident in these transgenic mice. In addition, TcR gamma 4 transgenic mice possessed a significantly elevated level of myelopoietic pluripotential precursors. 3H-thymidine cell suicide studies suggest that higher percentages of pluripotent precursors from the bone marrow of the TcR gamma 4 transgenic mice were in the S phase of the cell cycle. These modulations of the lymphoid and myelopoietic compartments, however, were not found in other T-cell receptor transgenic mice (e.g., TcR V gamma 1.2J gamma 2C gamma 2, TcR gamma 2; or V beta 8.1D beta J beta 2.4C beta 2, TcR beta) constructed with the same or similar cDNA expression vector. The results suggest that the expression of a specific T-cell receptor gamma chain gene, and/or an elevated level of particular subset of TcR gamma delta cells, may affect the proliferation and relative proportions of haemopoietic and lymphoid precursors.

Aging↗
PubMed1991

B cell commitment.

Multipotential stem cells have the capacity to differentiate into a variety of cell types including B lymphocytes. The development of B cells from multipotential progenitors has been the subject of numerous studies and many aspects of this transition are well characterized. However, the initial genetic events which commit a stem cell to follow the B lineage developmental pathway have not yet been discovered. In this review we examine diverse experiments which may lead to increased understanding of the important first steps in the commitment process.

Animals↗
PubMed1990

The influence of S17 stromal cells and interleukin 7 on B cell development.

A clonal assay was used to study different stimuli involved in the progression of fetal liver B cell precursors to mature B lymphocytes. In this report we replaced fetal liver heterogenous feeder cells by a recombinant growth factor, interleukin 7 (IL 7), and a clonal stromal cell line, S17. Under those conditions we could clone 1 in 10 B220+ B cell precursors from fetal liver and the cells could differentiate to a mitogen-responsive, immunoglobulin-secreting stage. We found that IL 7 stimulates proliferation of B220+ precursors but is not sufficient to support maturation of those precursors to a stage of mitogen responsiveness. We show further that the cell line S17 does not produce IL 7 at functionally detectable level but provides support for B cell maturation. We conclude that this cell line supplies an exogenous stimulus required by B cell precursors to become mature lymphocytes. We describe therefore two stages in pre-B cell development: (a) IL 7-dependent proliferation and (b) S17-dependent maturation to mitogen reactivity. Further studies demonstrate that S17 has a profound effect on B cells by increasing the clonal efficiency of lipopolysaccharide-responsive cells to nearly 1:1 B cell in the spleen of adult C57BL/6 mice.

Agar↗
PubMed1988

Modulation of antibody binding affinity by somatic mutation.

The affinity of hapten binding of monoclonal antibodies (MAbs) specific for 4-hydroxy-3-nitrophenylacetyl (NP) has been investigated at the molecular level by both site-specific mutagenesis and recombinant antibody construction, followed by expression in myeloma cells. We have shown that a single point mutation (trp----leu at codon 33) in the variable region of the heavy chain (VH) is sufficient to endow a primary-response, germline-encoded antibody with an affinity for antigen typical of a secondary-response antibody carrying the same mutation. We have also demonstrated that mutations additional to the trp----leu exchange in the heavy chain and further mutations in the light chain are irrelevant to the high-affinity phenotype of secondary-response antibodies. Since some of these are "parallel" mutations common to clonally unrelated antibodies, this suggests that the mutation rate is not constant across the entire immunoglobulin variable region. Although antibodies with a trp----leu exchange at position 33 are positively selected because of improved hapten binding affinity, we have found that, under rare circumstances, other patterns of mutations may be selected through particular D-JH combinations; we have demonstrated one case where this has generated an antibody with very efficient hapten binding ability.

Animals↗
PubMed1988

Antibody engineering for the analysis of affinity maturation of an anti-hapten response.

The influence of structural variation, previously observed in a panel of V186.2 VH/V lambda 1-expressing anti-NP antibodies from the secondary response, on the affinity of these antibodies was examined by site-specific mutagenesis and recombinant antibody construction. A tryptophan----leucine exchange at position 33 in the VH segment of all but one of the high-affinity antibodies is the most frequently observed somatic mutation and by itself leads to a 10-fold higher affinity; all other somatic exchanges are irrelevant for affinity selection. In the single case of a high-affinity antibody without this common exchange, high affinity is mediated by a combination of mutations (including a one-codon deletion) in VH and the particular D-JH rearrangement carried by this antibody. The data indicate that the pattern of somatic diversification through hypermutation is shaped by affinity selection, but that only a single point mutation is available in the VH and the VL gene of lambda 1 chain-bearing anti-NP antibodies which by itself leads to an increase of hapten-binding affinity. Based on the analysis of two secondary response antibodies from which somatic mutations in VH and VL have been eliminated, it is also concluded that the recruitment of B cell clones into the pathway of hypermutation involves a mechanism which is not based upon affinity differences towards the antigen.

Amino Acid Sequence↗
PubMed1987

Evolutionary and somatic selection of the antibody repertoire in the mouse.

The repertoire of antibody variable (V) regions has been subject to evolutionary selection, affecting both the diversity of V region genes in the germline and their expression in the B lymphocyte population and its subsets. In ontogeny, contact with an antigen leads to the expansion of B cells expressing antibodies complementary to it. In a defined phase of B cell differentiation, new sets of V regions are generated from the existing repertoire through somatic hypermutation. Cells carrying advantageous antibody mutants are selected into the memory compartment and produce a stable secondary response upon reexposure to the antigen.

Animals↗
PubMed1987

Timing, genetic requirements and functional consequences of somatic hypermutation during B-cell development.

While somatic antibody mutants are rare in the preimmune repertoire and in primary immune responses, they dominate secondary and hyperimmune responses. We present evidence that somatic hypermutation is restricted to a particular pathway of B-cell differentiation in which distinct sets of B-cell clones are driven into the memory compartment. In accord with earlier results of McKean et al. (1984) and Rudikoff et al. (1984), somatic mutation occurs stepwise in the course of clonal expansion, before and after isotype switch, presumably at a rate close to 1 X 10(-3) per base pair per generation. At this rate, both selectable and unselectable mutations accumulate in the rearranged V region genes. The distribution of replacement mutations in the V regions shows that a fraction of the mutations in CDRs is positively selected whereas replacement mutations are counterselected in the FRs. By constructing an antibody mutant through site-specific mutagenesis we show that a point mutation in CDR1 of the heavy chain, found in most secondary anti-NP antibodies, is sufficient to increase NP binding affinity to the level typical for the secondary response. Somatic mutation may contribute to the immune repertoire in a more general sense than merely the diversification of a specific response. We have evidence that clones producing antibodies which no longer bind the immunizing antigen can be kept in the system and remain available for stimulation by a different antigen. Somatic mutations are 10 times less frequent in DJH loci than in either expressed or non-expressed rearranged VDJH or VJ loci. We therefore conclude that a V gene has to be brought into the proximity of the DJH segment in order to fully activate the hypermutational mechanism in these loci.

Animals↗
PubMed1986

Clonal recruitment and somatic mutation in the generation of immunological memory to the hapten NP.

The nucleotide sequences of the variable regions of lambda 1 chain bearing anti-NP antibodies from the secondary response of C57BL/6 mice were determined. The data indicate that the V186.2 VH gene which dominates the primary anti-NP response is expressed in nine out of 10 secondary response antibodies and is extensively mutated. In the V lambda 1 regions somatic mutations are less frequent. While point mutations predominate, there is suggestive evidence for two conversion events, one involving a one-codon deletion. Most, but not all, secondary response antibodies have a higher affinity (up to 10-fold) for the hapten than is seen in the primary response. The increase in affinity correlates with 'parallel' mutations in CDRs of H and L chains, likely to play a role in hapten binding. The analysis of VDJH rearrangements demonstrates that the secondary response lambda 1 chain-bearing antibodies are produced by a diverse set of B cell clones, which are only rarely expressed in primary responses. These clones are characterized by N-sequence-mediated heterogeneity in the 3' half of CDR3, where the germ line sequence of the D element DFl16.1 predominates in primary response antibodies. The antibodies analyzed in this and in previous work were isolated from idiotypically suppressed mice in order to evaluate whether, intraclonally, idiotype suppression selects antibody mutants into the memory pool, through suppression of the wild-type. A selection of this type was not detectable. However, idiotype suppression may control the pattern of clonotypes expressed in the primary versus the secondary response.

Animals↗
PubMed1985

Structure of primary anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibodies in normal and idiotypically suppressed C57BL/6 mice.

Eight monoclonal antibodies from the primary response of C57BL/6 mice against the hapten (4-hydroxy-3-nitrophenyl)acetyl (NP) were isolated. The antibodies carry lambda 1 light chains and have similar affinities for the immunizing hapten. Sequence analysis at the level of mRNA reveals that all antibodies express the VH gene 186.2 and all but one the DFl 16.1 gene segment. The J segment of the heavy chain is JH2 in six cases and JH4 in two. Somatic point mutations are scarcely detectable in the antibodies, but there is extensive sequence variability at the boundaries of the D gene segment, mainly at its 5' end. However, seven of eight antibodies express tyrosine in position 99 of the heavy chain, encoded either by the 5' codon of DFl 16.1 or by presumed N sequences. In the former case, the tyrosine is the first of a stretch of three (positions 99-101). In the latter, a similar stretch (positions 99, 101, 102) is interrupted by aspartic acid, asparagine or cysteine in position 100. These variations profoundly affect idiotypic specificity. Six of the eight monoclonal antibodies came from mice neonatally suppressed by an anti-idiotope antibody whose target idiotope is regularly expressed in primary anti-NP responses and depends upon a non-germ-line-encoded aspartic acid in position 100 of the heavy chain. The sequence data show that the mice circumvent suppression by expressing antibodies which lack this aspartic acid but are otherwise structurally very similar to anti-NP antibodies from normal animals. Since suppression in the animals is partly controlled by regulatory T cells, we conclude that these T cells are highly restricted in their specificity in that they preferentially see a determinant which also depends upon the aspartic acid in position 100. The data suggest that the VH to D boundary serves as a target of idiotypic selection.

Amino Acid Sequence↗
PubMed1985

Low affinity of kappa chain bearing (4-hydroxy-3-nitrophenyl)acetyl (NP)-specific antibodies in the primary antibody repertoire of C57BL/6 mice may explain lambda chain dominance in primary anti-NP responses.

The primary anti-(4-hydroxy-3-nitrophenyl)acetyl (anti-NP) antibody response of C57BL/6 mice was analyzed by several methods. Serum analyses by solid-phase radioimmunoassay (RIA) showed that stimulation with the thymus-independent (TI) type 1 antigen NP-LPS results in an anti-NP antibody response dominated by kappa (kappa) light chain bearing antibodies, whilst responses to NP-Ficoll (a TI-2 antigen) and NP-KLH (a thymus dependent antigen) are dominated by lambda (lambda) 1 light chain bearing antibodies. However, in all these responses NP-specific plaque-forming cells (PFCs) were predominantly heteroclitic, and inhibitable by anti-lambda antiserum. In addition, kappa-bearing IgM-producing hybridomas obtained by fusion of spleen cells from NP-LPS-immunized mice, although producing NP-specific antibodies detectable by RIA, were unable to produce NP-specific plaques. Direct determination of the affinity of 5 of those hybridomas by fluorometric titrations showed that their affinity is indeed lower than 10(-5) M. These results suggest that most NP-specific antibodies stimulated by NP-LPS are of too low affinity to be detected in a direct PFC assay, with the exception of a population of lambda-bearing antibodies. Therefore, the differential expression of kappa- or lambda-bearing antibodies in primary responses to the hapten NP presented on different carriers may be due to different affinity requirements for B-cell triggering via different activation pathways.

Animals↗
PubMedDate not supplied

Effects of hydroxyurea in vivo treatment on the antibody response in mice.

In the present work, we investigate the effects of hydroxyurea (HU) treatment given before antigen priming on the antibody response in the mouse. We have studied the response to both thymus-independent and thymus-dependent antigens. With both types of antigens, we have found a two- to ten-fold increase in the number of antigen-specific IgM PFC in the spleens of HU-treated primed mice. In the case of the T-dependent antigens, a simultaneous decrease in the IgG PFC response was also observed in HU-treated mice. These results suggest that major changes in the dynamic equilibrium of the cells of the immune system, induced by HU treatment, may result in different homeostatic regulation, as revealed by the modified pattern of response to exogenous antigens.

Animals↗