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B Seed

Publications and source records attributed to B Seed.

At least 73 records · Page 4Linked to original sources
PubMed1989

Leu-8/TQ1 is the human equivalent of the Mel-14 lymph node homing receptor.

The human pan-leukocyte antigen Leu-8 has attracted wide interest because its presence or absence identifies suppressor-inducer and helper-inducer CD4+ T-lymphocyte subsets respectively. We report here that Leu-8 is the human homologue of the mouse Mel-14 homing receptor, a molecule that promotes the initial adhesion of blood-borne lymphocytes to the specialized post-capillary endothelium of peripheral lymph nodes. We also show that Leu-8 can adopt both conventional and phospholipid anchored forms, a finding that may have relevance in the context of antigen shedding following activation or homing. The assignment of lymphocytes to different functional classes based on lymph node homing potential may represent a more general association between lymphocyte function and tissue distribution.

Amino Acid Sequence↗
PubMed1989

Expression of cDNA clones encoding the thymocyte antigens CD1a, b, c demonstrates a hierarchy of exclusion in fibroblasts.

The CD1 gene family encodes at least three proteins: CD1a, CD1b, and CD1c, which are coexpressed on cortical thymocytes and a number of T cell leukemias. On thymocytes, CD1a forms noncovalent complexes with CD1b and CD1c, and a disulfide-linked heterodimer with CD8. This report describes the isolation and characterization of cDNA clones encoding the CD1a, CD1b, and CD1c Ag. Cotransfection of the cDNA was used to investigate the formation of intermolecular heterodimers by CD1a with other members of the CD1 gene family and with CD8. No intermolecular heterodimers were observed during transient expression in COS cells. However, an exclusion hierarchy was observed between members of the CD1 gene family when two or more members of the family were cotransfected into COS cells.

Amino Acid Sequence↗
PubMed1989

CD36 directly mediates cytoadherence of Plasmodium falciparum parasitized erythrocytes.

Erythrocytes infected with P. falciparum express knob-like adhesion structures that allow the infected cells to cling to the postcapilliary endothelium of characteristic host organs. At present, the mechanism of cytoadherence is not fully understood. While parasitized erythrocytes have been shown to specifically bind to the platelet/matrix molecule thrombospondin, adherence to suitable target cells can also be blocked by monoclonal antibody OKM5, which recognizes a surface molecule expressed by hematopoietic cells and endothelium. In apparent reconciliation of these findings, it has been reported that the OKM5 antigen (CD36) is a receptor for thrombospondin. Here we report that expression of a CD36 cDNA clone in COS cells supports cytoadherence of parasitized erythrocytes but does not support increased binding of purified human thrombospondin.

Amino Acid Sequence↗
PubMed1989

The primary structure of the human leukocyte antigen CD37, a species homologue of the rat MRC OX-44 antigen.

Comparison of NH2-terminal protein sequence from the rat OX-44 antigen with the sequence of the human CD37 antigen deduced from a cDNA clone shows that these antigens are species homologues. The CD37 sequence is 244 amino acids in length and lacks a conventional leader sequence. The molecule is likely to have an NH2-terminal cytoplasmic domain followed by three transmembrane sequences that lie within the first 110 amino acids. The rest of the molecule is hydrophillic and contains three sites for N-linked glycosylation.

Amino Acid Sequence↗
PubMed1989

A lymphocyte molecule implicated in lymph node homing is a member of the cartilage link protein family.

Monoclonal antibodies in the Hermes family recognize a lymphocyte structure that participates in lymphocyte adhesion to endothelium and has been suggested to be the human homolog of the murine Mel-14 lymph node homing receptor. Recently, antibodies against the Hermes antigen, the polymorphic glycoprotein Pgp-1 antigen, and the broadly expressed CDw44 antigen have been shown to recognize the same structure. In this work, cDNA clones encoding the CDw44 antigen were isolated and expressed in COS cells. Two forms were identified: a lymphoid form expressed in hematopoietic cells, and an epithelial form weakly expressed in normal epithelium but highly expressed in carcinomas. The extracellular domain of CDw44 bears homology to cartilage link proteins and a related segment of proteoglycan core protein. However, comparison with the recently identified sequence of the Mel-14 antigen shows that CDw44 and Mel-14 are unrelated.

Amino Acid Sequence↗
PubMed1989

Endothelial leukocyte adhesion molecule 1: an inducible receptor for neutrophils related to complement regulatory proteins and lectins.

Focal adhesion of leukocytes to the blood vessel lining is a key step in inflammation and certain vascular disease processes. Endothelial leukocyte adhesion molecule-1 (ELAM-1), a cell surface glycoprotein expressed by cytokine-activated endothelium, mediates the adhesion of blood neutrophils. A full-length complementary DNA (cDNA) for ELAM-1 has now been isolated by transient expression in COS cells. Cells transfected with the ELAM-1 clone express a surface structure recognized by two ELAM-1 specific monoclonal antibodies (H4/18 and H18/7) and support the adhesion of isolated human neutrophils and the promyelocytic cell line HL-60. Expression of ELAM-1 transcripts in cultured human endothelial cells is induced by cytokines, reaching a maximum at 2 to 4 hours and decaying by 24 hours; cell surface expression of ELAM-1 protein parallels that of the mRNA. The primary sequence of ELAM-1 predicts an amino-terminal lectin-like domain, an EGF domain, and six tandem repetitive motifs (about 60 amino acids each) related to those found in complement regulatory proteins. A similar domain structure is also found in the MEL-14 lymphocyte cell surface homing receptor, and in granule-membrane protein 140, a membrane glycoprotein of platelet and endothelial secretory granules that can be rapidly mobilized (less than 5 minutes) to the cell surface by thrombin and other stimuli. Thus, ELAM-1 may be a member of a nascent gene family of cell surface molecules involved in the regulation of inflammatory and immunological events at the interface of vessel wall and blood.

Amino Acid Sequence↗
PubMed1989

Isolation and expression of functional high-affinity Fc receptor complementary DNAs.

Human and murine mononuclear phagocytes express a high-affinity receptor for immunoglobulin G that plays a central role in macrophage antibody-dependent cellular cytotoxicity and clearance of immune complexes. The receptor (FcRI) may also be involved in CD4-independent infection of human macrophages by human immunodeficiency virus. This report describes the isolation of cDNA clones encoding the human FcRI by a ligand-mediated selection technique. Expression of the cDNAs in COS cells gave rise to immunoglobulin G binding of the expected affinity and subtype specificity. RNA blot analysis revealed expression of a 1.7-kilobase transcript in macrophages and in cells of the promonocytic cell line U937 induced with interferon-gamma. The extracellular region of FcRI consists of three immunoglobulin-like domains, two of which share homology with low-affinity receptor domains.

Amino Acid Sequence↗
PubMed1989

A B-lymphocyte activation molecule related to the nerve growth factor receptor and induced by cytokines in carcinomas.

B cells and primary carcinomas express a surface molecule, Bp50 (CDw40), absent from other hematopoietic cells and from normal epithelium, and thought to play a regulatory role in B-cell maturation and epithelial neoplasia. In this work the sequence of a cDNA clone encoding Bp50 was analyzed by a newly derived transition matrix method. Among several interesting relationships with known receptors was found an extensive homology with the nerve growth factor receptor. The mRNA is induced by gamma-interferon in both B cells and epithelial neoplasms, suggesting a role for the molecule in the development of carcinomas at sites of chronic inflammation.

Amino Acid Sequence↗
PubMed1989

A human macrophage-associated antigen (CD68) detected by six different monoclonal antibodies.

Antibodies grouped together by the Third Workshop on Leucocyte Differentiation Antigens on the basis of pan-macrophage reactivity on tissue sections were analysed in immunoprecipitation experiments. Antibodies Y2/131, EBM11, Ki-M6 and Ki-M7 all precipitated antigens of Mr 110,000 which were shown to be identical by preclearing experiments. In addition a recently produced antibody, KP1, which identifies macrophages in paraffin-embedded tissue, was shown to recognize the same antigen. The antibodies were tested on murine cells transfected with two clones, which had been isolated by screening a cDNA library with antibodies Y1/82A and EBM11. Cells transfected with the longer cDNA clone, coding for a molecule of Mr 110,000, reacted with antibodies Y2/131, EBM11, Y1/82A and Ki-M6, whilst the shorter clone, encoding a molecule of Mr 70,000 gave the same result except that it did not induce expression of the Ki-M6 epitope. KP1 antibody did not recognize any transfectants, possibly because of differences in glycosylation by the transfected cell line compared with human tissue. Five of the six antibodies appear to recognize different epitopes (the sixth, Ki-M7, not having been evaluated in this way). It was concluded that these six antibodies react with a macrophage-associated antigen for which the gene has been cloned. This group of antibodies has recently been designated CD68 by the Fourth Workshop on Human Leucocyte Differentiation Antigens.

Antibodies, Monoclonal↗
PubMed1989

Monocyte antigen CD14 is a phospholipid anchored membrane protein.

A cDNA clone encoding the human monocyte antigen CD14 was isolated by transient expression in COS cells of a cDNA library prepared from phorbol diester-treated HL60 cells. RNA blot analysis showed abundant expression of a single mRNA species in mature monocytes and an increased expression of the mRNA following induction of differentiation in leukemic cell lines. The DNA blot hybridization pattern was consistent with a single-copy gene. The predicted amino acid sequence lacks the characteristic transmembrane domain and stop transfer motif of conventionally anchored membrane proteins. COS cells transfected with the CD14 cDNA released virtually all CD14 protein in soluble form following treatment with glycosyl phosphatidylinositol-specific phospholipase C, and CD14 immunoreactivity was absent from the affected monocytes of a patient with paroxysmal nocturnal hemoglobinuria (PNH). The data show that, to the limit of experimental sensitivity, all monocyte CD14 is joined to the plasma membrane by a phosphatidylinositol phospholipid.

Amino Acid Sequence↗
PubMed1988

Isolation of a cDNA encoding CD33, a differentiation antigen of myeloid progenitor cells.

A cDNA clone encoding the human myeloid Ag CD33 was isolated from a U937 cDNA library after three rounds of transient expression in COS cells and enrichment by panning. COS cells transfected with the isolated clone expressed a surface protein recognized by the anti-CD33 mAb MY9, L1B2, and L4F3, having mass similar to but slightly smaller than the mass of CD33 expressed on myeloid cells. CD33 transcripts were found constitutively expressed in several myeloid progenitor cell lines. The cDNA sequence predicts a 40-kDa polypeptide with the typical features of a glycosylated integral membrane protein. The extracellular part of CD33 contains two Ig-like domains which are highly related to the first two domains of the neural cell myelin-associated glycoprotein and the B cell Ag CD22.

Amino Acid Sequence↗
PubMed1988

CD19, the earliest differentiation antigen of the B cell lineage, bears three extracellular immunoglobulin-like domains and an Epstein-Barr virus-related cytoplasmic tail.

The isolation and expression of a full-length cDNA clone encoding the B cell-specific glycoprotein CD19 is reported. The sequence of the cDNA predicts a glycosylated integral membrane protein with a precursor molecular weight of 51.8 x 10(3) and an extracellular domain organized into three contiguous Ig-like sub-domains. The cytoplasmic domain bears significant relatedness to two proteins encoded by the Epstein-Barr virus and the int-1 oncogene. CD19 transcripts are restricted to members of the B cell lineage, being most abundant in pre-B cell lines and least abundant in plasmacytomas.

Amino Acid Sequence↗
PubMed1988

Cloning and expression of the human interleukin-6 (BSF-2/IFN beta 2) receptor.

Interleukin-6 (IL-6/BSF-2/IFN beta 2) is a multifunctional cytokine that regulates the growth and differentiation of various tissues, and is known particularly for its role in the immune response and acute phase reactions. A complementary DNA encoding the human IL-6 receptor (IL-6-R) has now been isolated. The IL-6-R consists of 468 amino acids, including a signal peptide of approximately 19 amino acids and a domain of approximately 90 amino acids that is similar to a domain in the immunoglobulin (Ig) superfamily. The cytoplasmic domain of approximately 82 amino acids lacks a tyrosine/kinase domain, unlike other growth factor receptors.

Amino Acid Sequence↗
PubMed1988

A simple phase-extraction assay for chloramphenicol acyltransferase activity.

A simple and convenient phase extraction assay for chloramphenicol (Cm) acetyltransferase (CAT) activity has been developed, based on the enzymatic butyrylation of radiolabelled Cm. The assay is linear over two to three orders of magnitude of enzyme concentration, is highly sensitive, and substantially less expensive than all presently available alternatives. Methods for convenient CAT assay, adapted for mammalian cells, plant protoplasts, and mammalian cell culture supernatants, are described. These methods should also simplify measurement of CAT activity in other organisms, such as yeast and bacteria. In addition, a simple pre-extraction procedure is presented for purifying radiolabelled Cm which allows a 25-fold increase in sensitivity using tritiated substrates.

Animals↗
PubMed1988

Genetic analysis of monoclonal antibody and HIV binding sites on the human lymphocyte antigen CD4.

Saturation mutagenesis and a complement fixation selection have yielded CD4 point mutants with impaired antibody and human immunodeficiency virus binding. The patterns of amino acid substitution, in conjunction with previous antibody cross-blocking data, affirm the similar tertiary structures of the CD4 amino-terminal domain and immunoglobulin variable regions. Single residue substitutions affecting virus binding and syncytium formation are observed over an eight residue segment located in a portion of the molecule homologous to the second hypervariable region of an antibody combining site.

Amino Acid Sequence↗
PubMed1988

The Fc gamma receptor of natural killer cells is a phospholipid-linked membrane protein.

Three types of receptor for the Fc (constant) region of human immunoglobulin G have been described; FcRI, a high-affinity (Ka approximately equal to 10(8) M-1) receptor expressed on monocytes; FcRII (CD32), a low-affinity (Ka approximately equal to 10(6) M-1) receptor expressed on B cells, granulocytes, macrophages and platelets; and FcRIII (CD16, FcRIo), a low-affinity receptor expressed on macrophages, neutrophils, eosinophils, natural killer cells and a subset of T cells believed to comprise the suppressor cells. Anti-CD16 antibodies block natural killer-cell mediated antibody dependent cellular cytotoxicity (ADCC). Binding of aggregated IgG to CD16 on natural killer cells leads to the expression of lymphocyte activation antigens, mediator release, morphological changes and lytic activity. We report here the isolation of a complementary DNA clone encoding CD16 determinants which gave rise to IgG binding of the expected affinity and subtype specificity in COS cells, and which proved to encode a phospholipid anchored protein. A single messenger RNA transcript was found in all positive RNA samples, and N-glycanase treatment showed the form found in COS cells was identical to the form present on peripheral blood mononuclear cells (PBMCs). We also show that CD16 is most closely related to the alpha-form of the murine IgG 2b/1 receptor and propose that extracellular contacts mediate the signal initiated by IgG binding.

Amino Acid Sequence↗
PubMed1988

Analysis of two cDNA clones encoding the B lymphocyte antigen CD20 (B1, Bp35), a type III integral membrane protein.

Two cDNA clones encoding the pan-B cell CD20 antigen were isolated from a COS cell expression library. The two clones bear identical coding sequences and differ only in the length of the 3' untranslated region. The predicted CD20 sequence is 297 residues long and contains three hydrophobic domains, one of which is long enough to span the membrane twice. COS cells transfected with either CD20 clone express an immunoreactive protein of 33 kD.

Amino Acid Sequence↗