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Biomedical subjects

D Tarlinton

Publications and source records attributed to D Tarlinton.

At least 19 recordsLinked to original sources
PubMed2000

Homeodomain factor Nkx2-3 controls regional expression of leukocyte homing coreceptor MAdCAM-1 in specialized endothelial cells of the viscera.

Regulated emigration of blood-borne leukocytes plays a defining role in lymphoid organ development, immune surveillance, and inflammatory responses. We report here that mice deficient in the homeobox gene Nkx2-3, expressed in developing visceral mesoderm, show a complex intestinal malabsorption phenotype and striking abnormalities of gut-associated lymphoid tissue and spleen suggestive of deranged leukocyte homing. Mutant Peyer's patches were reduced in number and size, intestinal villi contained few IgA(+) plasma cells, and mutant spleens were small and often atrophic, showing fused periarterial lymphoid sheaths, partially merged T and B cell zones, an absent marginal zone, and a dearth of macrophages in red pulp. Semiquantitative RT-PCR analysis and immunohistochemistry revealed down-regulation of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in endothelial cells in which Nkx2-3 is normally expressed. MAdCAM-1 is a member of the immunoglobulin superfamily, acting as an endothelial cell ligand for leukocyte homing receptors L-selectin and alpha4beta7 integrin. Our data suggest a role for a homeodomain factor in establishing the developmental and positional cues in endothelia that regulate leukocyte homing through local control of cellular adhesion and identify MAdCAM-1 as a candidate target gene of Nkx2-3.

Animals↗
PubMed2000

bcl-2 transgene expression inhibits apoptosis in the germinal center and reveals differences in the selection of memory B cells and bone marrow antibody-forming cells.

Immunization with T cell-dependent antigens generates long-lived memory B cells and antibody-forming cells (AFCs). Both populations originate in germinal centers and, predominantly, produce antibodies with high affinity for antigen. The means by which germinal center B cells are recruited into these populations remains unclear. We have examined affinity maturation of antigen-specific B cells in mice expressing the cell death inhibitor bcl-2 as a transgene. Such mice had reduced apoptosis in germinal centers and an excessive number of memory B cells with a low frequency of V gene somatic mutation, including those mutations encoding amino acid exchanges known to enhance affinity. Despite the frequency of AFCs being increased in bcl-2-transgenic mice, the fraction secreting high-affinity antibody in the bone marrow at day 42 remained unchanged compared with controls. The inability of BCL-2 to alter selection of bone marrow AFCs is consistent with these cells being selected within the germinal center on the basis of their affinity being above some threshold rather than their survival being due to a selective competition for an antigen-based signal. Continuous competition for antigen does, however, explain formation of the memory compartment.

ADP-ribosyl Cyclase↗
PubMed1999

Genetic evidence for Lyn as a negative regulator of IL-4 signaling.

IL-4 has multiple effects on B lymphocytes, many of which are concentration dependent. This is particularly so for Ig isotype switching, where different thresholds of IL-4 stimulation are needed to induce switching from IgM to either IgG1 or IgE. In this report we describe a critical role for the tyrosine kinase Lyn in setting IL-4 signaling thresholds in mouse B lymphocytes. Upon CD40 ligand stimulation of lyn-/- B cells, 10-fold less IL-4 was required to induce switching from IgM to IgG1 and IgE and an increased proportion of B cells isotype switched at each IL-4 concentration. These in vitro results correlate with the in vivo findings that in lyn-/- mice, IgG1 Ab-forming cells develop prematurely in ontogeny and that adult lyn-/- mice have an abnormally high proportion of IgG1-expressing B cells in their spleens. Adult lyn-/- mice also have significantly higher levels of IgE in their serum. These results identify Lyn as a molecule involved in modulating the IL-4 signal in B cells and provide insights into its regulation and how a B cell signaling imbalance may contribute to atopy.

Animals↗
PubMed1998

Germinal centers: getting there is half the fun.

Several recent studies have provided new insights into how the infrequent B and T cells that are specific for a particular immunizing antigen come together to form the germinal centers that are crucial to the immune response.

Animals↗
PubMed1998

Germinal centers: form and function.

Our understanding of the formation of germinal centers has advanced considerably during the past year. Highlights include the elucidation of the role of cytokines and chemokines in splenic organization and lymphocyte migration and their roles in germinal center development. The functional consequences of recombination-activating gene re-expression in the germinal center have also been reported, as have in vitro models of somatic mutation. Finally the resolution of the germinal center reaction is being addressed by analysis of the individual cell types produced.

Animals↗
PubMed1997

Adult mice with targeted mutation of the interleukin-11 receptor (IL11Ra) display normal hematopoiesis.

Interleukin-11 (IL-11) is a pleiotropic growth factor with a prominent effect on megakaryopoiesis and thrombopoiesis. The receptor for IL-11 is a heterodimer of the signal transduction unit gp130 and a specific receptor component, the alpha-chain (IL-11R alpha). Two genes potentially encode the IL-11R alpha: the IL11Ra and IL11Ra2 genes. The IL11Ra gene is widely expressed in hematopoietic and other organs, whereas the IL11Ra2 gene is restricted to only some strains of mice and its expression is confined to testis, lymph node, and thymus. To investigate the essential actions mediated by the IL-11R alpha, we have generated mice with a null mutation of IL11Ra (IL11Ra-/-) by gene targeting. Analysis of IL11Ra expression by Northern blot and reverse transcriptase-polymerase chain reaction, as well as the absence of response of IL11Ra-/- bone marrow cells to IL-11 in hematopoietic assays, further confirmed the null mutation. Compensatory expression of the IL11Ra2 in bone marrow cells was not detected. IL11Ra-/- mice were healthy with normal numbers of peripheral blood white blood cells, hematocrit, and platelets. Bone marrow and spleen contained normal numbers of cells of all hematopoietic lineages, including megakaryocytes. Clonal cultures did not identify any perturbation of granulocyte-macrophage (GM), erythroid, or megakaryocyte progenitors. The number of day-12 colony-forming unit-spleen progenitors were similar in wild-type and IL11Ra-/- mice. The kinetics of recovery of peripheral blood white blood cells, platelets, and bone marrow GM progenitors after treatment with 5-flurouracil were the same in IL11Ra-/- and wild-type mice. Acute hemolytic stress was induced by phenylhydrazine and resulted in a 50% decrease in hematocrit. The recovery of hematocrit was comparable in IL11Ra-/ - and wild-type mice. These observations indicate that IL-11 receptor signalling is dispensable for adult hematopoiesis.

Animals↗
PubMed1997

Germinal centers: a second childhood for lymphocytes.

Recent observations show that, in the peripheral lymphoid organs known as germinal centers, lymphocytes appear to regain the phenotypic and molecular traits of immature cells; this cellular regression may play an important role in the affinity maturation of immune responses.

Animals↗
PubMed1995

Mice lacking the c-rel proto-oncogene exhibit defects in lymphocyte proliferation, humoral immunity, and interleukin-2 expression.

The c-rel proto-oncogene, which is expressed predominantly in hemopoietic cells encodes a subunit of the NF-kappa B-like family of transcription factors. In mice with an inactivated c-rel gene, whereas development of cells from all hemopoietic lineages appeared normal, humoral immunity was impaired and mature B and T cells were found to be unresponsive to most mitogenic stimuli. Phorbol ester and calcium ionophore costimulation, in contrast to certain membrane receptor-mediated signals, overcame the T cell-proliferative defect, demonstrating that T cell proliferation occurs by Rel-dependent and -independent mechanisms. The ability of exogenous interleukin-2 to restore T Cell, but not B cell, proliferation indicates that Rel regulates the expression of different genes in B and T cells that are crucial for cell division and immune function.

Aging↗
PubMed1995

DH element reading frame selection is influenced by an Ig heavy chain transgene, but not by bcl-2.

Mouse B cell precursors containing Ig DHJH junctions in one particular reading frame are selectively lost during B cell development. In this register, arbitrarily referred to as reading frame 2, DHJH junctions give rise to an open reading frame starting upstream of the DH element and including the DHJH-peptide fused to the constant region of IgM. Expression of this protein, called D mu, has been strongly implicated in the loss of B cell precursors containing reading frame 2 DHJH junctions. In an attempt to elucidate the means of D mu counterselection, we have examined the reading frame distribution of DHJH junctions in peripheral B cells from mice transgenic for either the human bcl-2 oncogene or for a functionally rearranged Ig mu heavy chain. In bcl-2 transgenic mice, reading frame 2 accounted for < 5% of the DHJH junctions in peripheral B cells, a value not significantly different from controls. Reading frames 1 and 3 were equally represented among the remaining junctions. By contrast, the reading frame distribution of endogenous DHJH junctions in splenic B cells from Ig mu heavy chain transgenic mice showed no evidence of bias against D mu encoding DHJH junctions. Reading frames 2 and 3 accounted for 27% and 30% of the sequenced DHJH junctions, respectively, and the remaining 43% were reading frame 1. Thus although the presence of BCL-2 cannot prevent the selective loss of reading frame 2 DHJH B cells, a functional mu heavy chain can. These results suggest that D mu-expressing B cell precursors may be selectively lost because of the premature and inappropriate cessation of heavy chain gene rearrangement rather than because of the induction of an apoptotic process which can be blocked by BCL-2.

Animals↗
PubMed1994

Absence of MHC class II expression distinguishes fetal from adult B lymphopoiesis in mice.

Early B-lineage progenitor cells (Pro-B) isolated from murine fetal liver and adult bone marrow can differentiate to the immature B cell stage in a stromal cell-dependent culture system and to mature B cells upon transfer into immunodeficient SCID mice. By using immunofluorescence analysis, we found that progenitor cells from day 16 fetus differentiating in culture lacked MHC class II expression during the Pre-B and immature B cell stages, whereas such expression was readily apparent on the surface of corresponding adult-derived populations. RT-PCR analysis of RNA message levels for the four class II genes (A alpha, A beta, E alpha, E beta) yielded completely concordant results. B cells of fetal progeny did eventually express class II upon further maturation in vivo. Thus, the onset of class II expression is uniquely delayed during fetal B cell differentiation. This result explains an apparent paradox, i.e., that class II expression is absent from B cells in neonatal spleen but present as early as the Pre-B cell stage in adult bone marrow. Furthermore, we suggest that such distinct programs of class II expression during fetal and adult lymphopoiesis could result in differences in susceptibility to tolerance.

Animals↗
PubMed1993

Direct demonstration of MHC class II surface expression on murine pre-B cells.

Using multi-parameter flow cytometry, MHC class II (Ia) antigens were found to be expressed at readily detectable levels on the majority of surface IgM- B lineage cells in the bone marrow of adult mice. Approximately 90% of the pre-B cells (B220+IgM-) in BALB/c bone marrow (BM) were MCH class II positive, while in C57BL/6 this figure was somewhat less, approximately 60%. Analysis of adult BM for the correlated expression of Ia both with heat stable antigen (HSA) and BP-1 on B lineage cells revealed in both cases a small fraction of cells expressing either the HSA or BP-1 but lacking Ia. This result suggests that the onset of expression of both HSA and BP-1 precede that of Ia in B cell development. When the B220loCD43+ pro-B cell compartment from BALB/c BM was analysed for the expression of Ia very few, if any, cells were found to be positive. Of the remaining B220+ cells, > 90% express detectable Ia. Thus the onset of Ia expression would appear to be soon after the pro-B cell compartment. The results presented here resolve the previous discrepancy between human and murine pre-B cell differentiation of when Ia is first expressed, and additionally, by identifying a new pre-B cell antigen, allow for the refinement of existing schemes of murine B cell development.

Animals↗
PubMed1992

T cell-dependent antibody production by Ly-1 B cells.

Through the use of a SCID transfer system, we have demonstrated that under certain conditions, the production of Ig by Ly-1 B cells can be modulated by T cells. This modulation can take the form of enhanced isotype production or isotype-switch induction and to some extent appears to be dependent on the activation state of the T cells. Furthermore we have shown that Ly-1 B cells can mount an idiotypically restricted T cell-dependent immune response to the antigen PC-KLH. This result suggests that the previous failure to observe T cell-dependent responses by Ly-1 B cells has been due to these B cells being "blind" to the antigens used and is not due to some inherent property of these B cells. When one considers the previous reports of the substantial contribution of Ly-1 B cells to the natural serum immunoglobulin levels and the ability of T cells to affect Ig production by Ly-1 B cells documented in this report, it is clear that the interaction of T cells with the Ly-1 B-cell population is important in determining the "natural" serum Ig repertoire of the mouse.

Animals↗
PubMed1992

An explanation for the defect in secretion of IgM Mott cells and their predominant occurrence in the Ly-1 B cell compartment.

Mott cells are a variant form of plasma cell in which the immunoglobulin (Ig), rather than being secreted, accumulates in rough endoplasmic reticulum-derived vesicles called Russell bodies. We have examined the molecular cause of this defect and the in vivo origin of IgM Mott cells. Our examination of the Ig variable region gene sequences of two IgM Mott hybridomas derived from C.B-20 Ly-1 B cells showed all to be germ line. In a series of mix and match transfection experiments, the Mott phenotype was only reconstituted when the original Mott specificity was expressed as an IgM, suggesting that both the specificity and the isotype were critical to the formation of Russell bodies. Based on our finding that Russell body formation was dependent on the Ig isotype being IgM, we suggest that the Mott phenotype is apparent only after differentiation of B cells into plasma cells and that probably the major cause of the IgM Mott phenotype is low-affinity interaction of the Mott Ig with some as yet unknown intracellular component(s) being stabilized by the intrinsic high avidity of the pentameric secreted form of IgM. Consistent with this proposal was the finding that after in vitro lipopolysaccharide (LPS) stimulation of sorted Ly-1 B cells derived from C.B-20 mice, Mott cells represented up to 5% of the IgM plasma cells in the culture. LPS stimulation of conventional B cells also induced the appearance of IgM Mott cells, but at the much reduced level of 0.1%, suggesting that the major, if not the only, source of Mott cells in vivo is the Ly-1 B cell population. A possible causal relationship between the elevated frequency of Mott cells in the Ly-1 B cell-derived LPS blasts and the repertoire selection inherent in the development of these B cells is discussed.

Amino Acid Sequence↗
PubMed1991

Most peripheral B cells in mice are ligand selected.

Using amplified cDNA and genomic libraries, we have analyzed the VH gene repertoire of pre-B cells and various B cell subsets of conventional mice at the level of VH genes belonging to the J558 VH gene family. The sequence data were evaluated on the basis of a newly established list of 67 J558 VH genes that comprise approximately two-thirds of the J558 VH genes of the murine IgHb haplotype. The results of the analysis demonstrate that VH gene utilization in pre-B cells, although biased to some extent by B cell autonomous VH gene selection, scatters over the whole range of J558 VH genes present in the germline. In contrast, in mature, peripheral B cells comprising long-lived mu + delta high B cells as well as Ly-1 B cells, small overlapping sets of germline VH genes are dominantly expressed. The data indicate that the recruitment of newly generated B cells into the long-lived peripheral B cell pool is mediated through positive selection by internal and/or external antigens. Because of the absence of immunoglobulin class switching and somatic hypermutation, this process is different from the selection of memory B cells in T cell-dependent immune responses.

Animals↗
PubMed1988

Repetitive usage of immunoglobulin VH and D gene segments in CD5+ Ly-1 B clones of (NZB x NZW)F1 mice.

The usually small Ly-1 B cell population is markedly increased in older mice by expansion of certain clones. This results in a cellular picture very similar to human B chronic lymphocytic leukemia. Here we report a molecular analysis of the immunoglobulin gene rearrangements of the Ly-1 B cell populations in (NZB x NZW)F1 females. We find that (i) the number of clones found in the peritoneum (a major tissue source of Ly-1 B cells) decreases with age till mono- or biclonality is common by approximately 6 months, (ii) many clones from different mice show the same size rearrangements at both the Ig heavy and light chain loci and (iii) the IgH rearrangements found in a clone isolated from the spleen of one mouse are a subset of those found in the peritoneum of the same mouse, implying migration occurs from the peritoneum to the spleen. Molecular cloning and sequencing of the IgH rearrangements from the peritoneal clones of one B/W mouse revealed that all productive rearrangements used the identical unmutated VH and D elements joined to different JHS. Indeed, two VDJH4 rearrangements were recovered which were identical but for six junctional (N region) nucleotides. The conservation of VH and D segment usage in the rearrangements of these Ly-1 B cell clones could indicate some strong selective pressure for clonal expansion (for example antigen selection) operates via the immunoglobulin molecules of these cells. Southern analyses of other (NZB x NZW)F1 mice with this cloned VH and the usage of the same or similar VH genes among a number of Ly-1 B origin tumors in other mouse strains indicate the generality of this repetitive VH gene usage in individual mice.

Antigens, Differentiation↗