Biomedical subjects

E L Masteller

Publications and source records attributed to E L Masteller.

11 recordsLinked to original sources

PubMed2000

Structural analysis of CTLA-4 function in vivo.

CTLA-4-mediated inhibition of T cell activation may be accomplished by competition for ligands and/or by signals mediated through the intracellular domain. Studies have implicated Tyr201 in the cytoplasmic domain of CTLA-4 in regulating CTLA-4 signal transduction and intracellular trafficking. To investigate the mechanism of CTLA-4 function in vivo, transgenes encoding wild-type CTLA-4 (FL), a mutant lacking the cytoplasmic domain of CTLA-4 (DeltaCTLA-4 tail), or a CTLA-4 Tyr201 mutant (Y201V) were introduced into CTLA-4-deficient mice. CTLA-4-/- mice display an autoimmune lymphoproliferative disorder resulting in tissue destruction and early death. When either the FL or the Y201V transgene was bred into CTLA-4-/- animals, a complete rescue from lymphoproliferation and autoimmunity was observed. In contrast, CTLA-4-/- mice expressing the DeltaCTLA-4 tail transgene were long lived with no evidence of multiorgan lymphocytic infiltration, but exhibited lymphadenopathy and accumulated large numbers of activated T cells. Furthermore, these animals displayed a Th2-biased phenotype which conferred susceptibility to Leishmania infection. These results indicate that the inhibitory effect of CTLA-4 is mediated in part through the ability of the extracellular domain to compete for ligands. The cytoplasmic domain of CTLA-4, however, is required for complete inhibitory function of the receptor and for regulation of Th cell differentiation in vivo.

Abatacept↗

PubMed1997

Avian B cell development.

Development of B cells in chickens proceeds via a series of discrete developmental stages that includes the maturation of committed B cell progenitors in the specialized microenvironment of the bursa of Fabricius. The bursa has been shown to be required for the amplification of the B cell pool and selects for cells with productive immunoglobulin rearrangement events. Other events regulating chicken B cell development such as lymphocyte trafficking and apoptosis are just beginning to be elucidated. Within the bursa, the variable regions of immunoglobulin genes of B cell progenitors are diversified by a process of intrachromosomal gene conversion, where blocks of sequence information are transferred from pseudo-V regions to the recombined variable regions of the immunoglobulin genes. Recently gene conversion has been determined to play a role in the diversification of the immune repertoire in other species. In this review we focus on the current understanding and recent advances of B cell development in the chicken.

Animals↗

PubMed1995

Expression of sialyl Lewis(x) and Lewis(x) defines distinct stages of chicken B cell maturation.

Commitment of cells to the B lineage in chickens occurs only during a brief period of embryogenesis. B cell progenitors then progress through discrete developmental stages resulting in the production of mature B cells that are competent to form a functioning humoral immune system in the adult bird. During embryogenesis, chicken B cell precursors undergo tissue and developmental stage-specific changes in cell-surface glycosylation. Immature B cell progenitors that migrate to the bursa of Fabricius express the carbohydrate epitope sialyl Lewis(x). Such cells undergo initial clonal expansion within the bursa without undergoing gene conversion. Beginning between days 15 and 17 of embryogenesis, B cells in the bursa undergo a tissue specific change in surface glycosylation that results in the loss of sialyl Lewis(x) expression and the acquisition of the related carbohydrate structure Lewis(x). Expression of Lewis(x) identifies B lymphocytes that have begun to undergo gene conversion. Before emigration from the bursa, bursal lymphocytes undergo another phenotypic switch in glycosylation and down-regulate Lewis(x) expression. Therefore, developmental switches in glycosylation allow us to distinguish three populations of B cells in the bursa of Fabricius at defined stages of development and suggest that regulation of cell-surface glycosylation plays a role in B cell development in the chicken.

Animals↗

PubMed1995

Chicken B cells undergo discrete developmental changes in surface carbohydrate structure that appear to play a role in directing lymphocyte migration during embryogenesis.

The migration of progenitor cells to specific microenvironments is essential for the development of complex organisms. Avian species possess a unique primary lymphoid organ, the bursa of Fabricius, that plays a central role in the development of B cells. B cell progenitors, however, arise outside the bursa of Fabricius and, during embryonic development, must migrate through the vasculature to the bursa of Fabricius. In this report, we demonstrate that these progenitor B cells express the sialyl Lewis x carbohydrate structure previously shown to be a ligand for the selectin family of vascular adhesion receptors. Soon after migration to the bursa of Fabricius, B cell progenitors are induced to undergo a developmental switch and terminate the expression of sialyl Lewis x in a temporal pattern that correlates with the developmental decline in the ability of these cells to home to the bursa of Fabricius upon transplantation. The induction of the developmental switch in the glycosylation pattern of developing B cells requires the bursal environment. In addition, sialyl Lewis x carbohydrate determinants or structurally similar determinants on the surface of immortalized bursal lymphoid stem cells participate in the adherence of these cells to the vascular regions of the bursal microenvironment. These data demonstrate that the carbohydrate structure sialyl Lewis x is developmentally regulated during chicken B cell development and may facilitate the migration of B cell progenitors to the bursal microenvironment by serving as a ligand for a lectin-like adhesion receptor.

Animals↗

PubMed1994

B cell development in the chicken.

A central feature of the vertebrate humoral immune system is that an organism must have a vast repertoire of antibodies to protect it against foreign pathogens. Chickens create a diverse immunological repertoire by intrachromosomal gene conversion of the single variable gene segments of the Ig heavy and light chain genes. This diversification process has been shown to require the bursa of Fabricius. Immature cells commit to the B cell lineage by rearranging their Ig genes prior to migration to the bursa. Recent work has suggested that the ability of a developing B cell to migrate to the bursa may depend on the expression of the carbohydrate structure sialyl Lewis x. Developing B cells in the spleen with the ability to migrate to the bursa have been shown to express sialyl Lewis x. Cells expressing sialyl Lewis x begin appearing in the bursa anlage between embryonic Days 10 and 12. These sialyl Lewis x-positive cells appear to form the nascent bursal follicles and are induced to proliferate. Coincident with the time that B cells initiate the gene conversion process, cells cease expressing sialyl Lewis x and begin expressing the related surface epitope Lewis x. As cells mature further, they undergo another phenotypic change and switch from expressing high levels of Lewis x to become Lewis x-low. At the same time that Lewis x-low cells accumulate in the bursa, cells with this phenotype begin to appear in the spleen. These phenotypic markers may be useful in identifying chicken B cells at different developmental stages.

Animals↗

PubMed1992

RAG-2 expression is not essential for chicken immunoglobulin gene conversion.

Chicken B cells diversify their immunoglobulin genes by gene conversion in the bursa of Fabricius. The avian leukosis virus-induced B-cell line DT40 continues to diversify its immunoglobulin light chain locus by gene conversion during in vitro passage. Since a variable(diversity)joining recombination-activating gene, RAG-2, is specifically expressed in chicken B cells undergoing immunoglobulin gene conversion, it has been suggested that RAG-2 may be involved in the immunoglobulin gene conversion process. We previously reported high ratios of targeted to random integration after transfection of genomic DNA constructs into DT40. This allows us to easily investigate the function of a gene product by gene disruption. We show here that subclones of DT40 maintain the ability to diversify their immunoglobulin light chain locus by gene conversion even after both copies of the RAG-2 coding regions are deleted. These results demonstrate that the RAG-2 product is not required for gene conversion activity in the immunoglobulin light chain locus.

Animals↗

PubMed1991

Selective expression of RAG-2 in chicken B cells undergoing immunoglobulin gene conversion.

Chickens create their immunoglobulin (Ig) repertoires during B cell development in the bursa of Fabricius by intrachromosomal gene conversion. Recent evidence has suggested that Ig gene conversion may involve cis-acting DNA elements related to those involved in V(D)J recombination. Therefore, we have examined the potential role of the V(D)J recombination activating genes, RAG-1 and RAG-2, in regulating chicken Ig gene conversion. In contrast to the coexpression of RAG-1 and RAG-2 observed in mammalian B cells that undergo V(D)J recombination, chicken B cells isolated from the bursa of Fabricius express high levels of the RAG-2 mRNA but do not express RAG-1 mRNA. The developmental and phenotypic characteristics of the bursal lymphocytes and chicken B cell lines that express RAG-2 mRNA demonstrate that selective RAG-2 expression occurs specifically in B cells undergoing Ig diversification by gene conversion. These data suggest that RAG-2 plays a fundamental role in Ig-specific gene conversion.

Actins↗

PubMed1989

The common acute lymphoblastic leukemia antigen gene maps to chromosomal region 3 (q21-q27).

Complementary DNA and genomic clones corresponding to the gene for the common acute lymphoblastic leukemia antigen (CALLA) were used to investigate the genetic structure and location of the CALLA locus. The gene, which encodes a 100-kDa type II transmembrane glycoprotein, appears to be a single copy locus of greater than 45 kb which is not rearranged in malignancies expressing cell surface CALLA. Cell hybrid analysis indicates that the CALLA-related DNA sequences are found on human chromosome 3. In situ hybridization studies reveal the regional location of the CALLA locus to be 3q21-27.

Animals↗

PubMed1989

Common acute lymphoblastic leukemia antigen (CALLA) is active neutral endopeptidase 24.11 ("enkephalinase"): direct evidence by cDNA transfection analysis.

The common acute lymphoblastic leukemia antigen (CALLA) is a 749-amino acid type II integral membrane protein expressed by most acute lymphoblastic leukemias, certain other lymphoid malignancies with an immature phenotype, and normal lymphoid progenitors. A computer search against the most recent GenBank release (no. 56) indicates that human CALLA cDNA encodes a protein nearly identical to the rat and rabbit neutral endopeptidase 24.11 ("enkephalinase;" EC 3.4.24.11). This zinc metalloendopeptidase, which has been shown to inactivate a variety of peptide hormones including enkephalin, chemotactic peptide, substance P, neurotensin, oxytocin, bradykinin, and angiotensins I and II, had not been identified in lymphoid cells. To determine whether CALLA cDNA derived from human acute lymphoblastic leukemia cells (Nalm-6 cell line) encodes functional neutral endopeptidase activity, we generated CALLA+ stable transfectants in the CALLA- murine myeloma cell line J558 and analyzed them for enzymatic activity in a fluorometric assay based upon cleavage of the substrate glutaryl-Ala-Ala-Phe 4-methoxy-2-naphthylamide at the Ala-Phe bond. Total lysates as well as whole-cell suspensions of the Nalm-6 line and of the CALLA+ transfectants, but not of the CALLA- J558 cells, possessed neutral endopeptidase activity. This enzymatic activity was associated with the cellular membrane fraction and was abrogated by the specific neutral endopeptidase inhibitor phosphoramidon. The unequivocal identification of CALLA as a functional neutral endopeptidase provides insight into its potential role in both normal and malignant lymphoid function.

Animals↗

PubMed1989

Organization of the gene encoding common acute lymphoblastic leukemia antigen (neutral endopeptidase 24.11): multiple miniexons and separate 5' untranslated regions.

The common acute lymphoblastic leukemia antigen (CALLA) is a 749-amino acid type II integral membrane protein that has been identified recently as the neutral endopeptidase 24.11 [NEP (EC 3.4.24.11)]. Herein, we characterize the organization of the human CALLA/NEP gene and show that it spans more than 80 kilobases (kb) and is composed of 24 exons. Exons 1 and 2 encode 5' untranslated sequences; exon 3 [170 base pairs (bp)] encodes the initiation codon and transmembrane and cytoplasmic domain; 20 short exons (exons 4-23), ranging in size from 36 to 162 bp, encode most of the extracellular portion of the enzyme; and exon 24 (approximately 3400 bp) encodes the COOH-terminal 32 amino acids of the protein and contains the entire 3' untranslated region (UTR). Of note, the pentapeptide sequence (His-Glu-Ile-Thr-His) associated with metalloprotease zinc binding and substrate catalysis is encoded within a single exon (exon 19). Three types of CALLA/NEP cDNAs have been identified: these clones contain 5' UTR sequences differing from one another upstream of exon 3. These human 5' sequences are homologous to those found in rat brain and rabbit kidney NEP cDNAs. The three human CALLA cDNA types result from alternative splicing of exons 1, 2a, or 2b to the common exon 3. Moreover, exons 2a and 2b share the same 5' sequence but differ from each other by the use of two distinct donor splice sites 171 bp apart in the gene. The substantial conservation of 5' untranslated sequences among species and the existence of 5' alternative splicing suggest that CALLA gene expression may be differentially controlled in a tissue-specific and/or developmentally regulated fashion.

Amino Acid Sequence↗

PubMed1988

Molecular cloning of the common acute lymphoblastic leukemia antigen (CALLA) identifies a type II integral membrane protein.

Common acute lymphoblastic leukemia antigen (CALLA) is a 100-kDa cell-surface glycoprotein expressed on most acute lymphoblastic leukemias and certain other immature lymphoid malignancies and on normal lymphoid progenitors. The latter are either uncommitted to B- or T-cell lineage or committed to only the earliest stages of B- or T-lymphocyte maturation. To elucidate to homogeneity, obtained the NH2-terminal sequence from both the intact protein and derived tryptic and V8 protease peptides and isolated CALLA cDNAs from a Nalm-6 cell line lambda gt10 library using redundant oligonucleotide probes. The CALLA cDNA sequence predicts a 750-amino acid integral membrane protein with a single 24-amino acid hydrophobic segment that could function as both a transmembrane region and a signal peptide. The COOH-terminal 700 amino acids, including six potential N-linked glycosylation sites compose the extracellular protein segment, whereas the 25 NH2-terminal amino acids remaining after cleavage of the initiation methionine form the cytoplasmic tail. CALLA+ cells contain CALLA transcripts of 2.7 to 5.7 kilobases with the major 5.7- and 3.7-kilobase mRNAs being preferentially expressed in specific cell types.

Amino Acid Sequence↗