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- Dueñas, M., et al.
(författare)
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A point mutation in a murine immunoglobulin V-region strongly influences the antibody yield in Escherichia coli
- 1995
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Ingår i: Gene. - 0378-1119. ; 158:1, s. 61-66
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Tidskriftsartikel (refereegranskat)abstract
- Recombinant DNA technology has made it possible to produce specific Fab and scFv antibody (Ab) fragments in prokaryotic host cells. Using vectors designed for periplasmic expression of encoded Ab fragments, we have been studying how the sequence and genetic localization of the light chain (L-chain) variable region gene of a mouse Ab (CB-Nm.1) determined the level of Ab production. The variable region was shown to belong to the VKV family and contained a previously unreported Ile72. Nine different Ab constructions were tested in monocistronic (scFv) or dicistronic (Fab) operons for their ability to affect the synthesis level of the L-chain. When the gene coding for the L-chain was located downstream from the Fd fragment gene, the substitution of codons encoding Ile by a codon encoding Thr was found to be crucial for any expression of the L-chain fragment. This was, however, not accompanied by an increase in L-chain-specific mRNA, neither was there any change in the size of the mRNA. The fact that the unmutated L-chain protein was produced from cells transformed with certain other constructions indicated that the protein as such was not incompatible with the prokaryotic environment. Together, this suggested that the translation process was involved in the restricted production of the L-chain. Thus, surprisingly small substitutions significantly affected the expression level, a fact that will have important implications on the library size expressed in prokaryotic hosts, including phagedisplayed Ab libraries.
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| 6. |
- Dueñas, M., et al.
(författare)
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In vitro immunization of naive human B cells yields high affinity immunuglobulin G antibodies as illustrated by phage display
- 1996
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Ingår i: Immunology. - 0019-2805. ; 89:1, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- In vitro antibody responses to a synthetic immunogen, consisting of both a B cell [V3 loop of gp120 from human immunodeficiency virus type 1 (HIV-1)] and a T-helper epitope (15 amino acids of tetanus toxoid) was studied. The in vitro activation was performed by primary and secondary in vitro immunizations, using lymphocytes obtained from uninfected, seronegative donors. Analysis of the in vitro immune response demonstrated an antigen-specific isotype switch, which was dependent on the presence of antigen-specific T-helper cells, CD40 ligation and antigen. Antibody libraries were constructed from cells derived directly from the naive donors, or from primary or secondary in vitro immunized B cells. Five libraries were displayed on filamentous phage and selected for anti-V3-specific Fab fragments, using a selection approach that linked recognition and phage replication. A panel of 19 recombinant antigen-specific Fab, representing different phases of the humoral in vitro immune response, were sequenced, expressed and analysed using a biosensor. Recombinant Fab fragments derived from cultures on day 12 exhibited an increase in affinity of close to two orders of magnitude compared to those obtained from cells primary immunized for 7 days. This study provides the first evidence that an antigen-specific in vitro immune response can yield high-affinity immunoglobuling G antibodies.
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| 7. |
- Eickmann, M., et al.
(författare)
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Effect of cysteine substitutions on dimerization and interfragment linkage of human cytomegalovirus glycoprotein B (gp UL55)
- 1998
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Ingår i: Archives of Virology. - : Springer Science and Business Media LLC. - 0304-8608 .- 1432-8798. ; 143:10, s. 1865-1880
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were carried out to analyze the function of cysteine residues at amino acid positions 506 (cI), 550 (cII), 573 (cIII), and 610 (cIV), in dimerization and/or disulfide linkage of human cytomegalovirus (HCMV) glycoprotein B (gB). Single c-codons or pairs were substituted in the gB sequence of constructs which were used for transfection and selection of stable transfectants. Analysis of gB expression products revealed that single substitutions of cIII or cIV, but neither single nor double substitutions of cI or/and cII prevented gB dimerization. All substituted gB derivatives were, however, no longer processed by proteolytic cleavage. After deletion of the membrane anchor domain, correct proteolytic processing was again observed for anchorless gB forms. Substitutions of cI or cI/cII in secretory gB appeared to interfere with disulfide linkage between gB cleavage fragments. In the case of anchorless gB with substitutions of cII, cIII, or cIII/cIV, however, extracellular gB forms were not recovered. Using the Sindbis expression system recovery of all anchorless gB forms with cysteine substitutions was achieved. Analysis verified involvement of cI/II substitutions in intrachain disulfide linkage between cleavage fragments of HCMV gB.
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| 8. |
- Ohlin, M., et al.
(författare)
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Human antibody reactivity against the lower matrix protein (pp65) produced by cytomegalovirus
- 1995
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Ingår i: Clinical and Diagnostic Laboratory Immunology. - 1071-412X. ; 2:3, s. 325-329
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Tidskriftsartikel (refereegranskat)abstract
- The lower matrix protein (pp65) is a major product of many laboratory strains of cytomegalovirus (CMV). It is thus an integral part of many CMV serological assays based on native antigen. Recombinant fragments of pp65 have previously been investigated for their usefulness in more-defined assays. The latter antigens have, however, failed to develop a positive response with serum samples derived from a substantial number of infected individuals. Here we show that the human humoral immune response to CMV pp65 is highly diverse and recognizes at least seven distinct but in some cases partly overlapping epitopes. Most of these epitopes could not be mimicked by any of the investigated recombinant or synthetic antigens. Furthermore, when we investigated the ability of human CMV-seropositive serum samples to block the reactivity of pp65 specific antibodies recognizing five different epitopes within pp65, it was evident that several sera did not contain significant levels of antibodies against any of these or overlapping structures. It was thus concluded that the antibody response against CMV pp65 is weak in some CMV-infected individuals, making this antigen unsuitable for use alone in serological screening systems for CMV infection.
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| 9. |
- Schoppel, K., et al.
(författare)
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Antibodies specific for the antigenic domain 1 of glycoprotein B (gpUL55) of human cytomegalovirus bind to different substructures
- 1996
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Ingår i: Virology. - : Elsevier BV. - 0042-6822. ; 216:1, s. 133-145
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Tidskriftsartikel (refereegranskat)abstract
- Glycoprotein B (gB, gpUL55) is a major antigen for the induction of neutralizing antibodies against human cytomegalovirus, making it an attractive antigen for active and passive immunoprophylaxis. The immunodominant region on gB is the antigenic domain 1 (AD-1), a complex structure which requires a minimal linear amino acid sequence of more than 75 amino acids (aa 552-635) for antibody binding. We have analyzed the fine specificity cf neutralizing and nonneutralizing AD-1-binding monoclonal antibodies. Point mutations were introduced into AD-1 and mutants were expressed as bacterial fusion proteins. The antigens were analyzed in immunoblots using a panel of 13 human and murine monoclonal antibodies. Complete loss of binding of all antibodies was observed with mutations at cysteine residues 573 and 610 as well as with a combinatorial exchange of prolines at position 577 and 613. The remaining mutations had different effects on antibody binding. Six individual recognition patterns were observed, indicating various antigenic substructures on AD-1. Changing the Fc portions of 3 murine monoclonal antibodies to human IgG1 showed that neutralization of AD-1-binding immunoglobulins is exerted by different mechanisms. Dependent on the recognized substructure within AD-1, avidity-dependent as well as Fc portion-mediated effects were observed.
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| 10. |
- Bold, S., et al.
(författare)
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Structural domains involved in human cytomegalovirus glycoprotein B-mediated cell-cell fusion
- 1996
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Ingår i: Journal of General Virology. - 0022-1317. ; 77:9, s. 2297-2302
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Tidskriftsartikel (refereegranskat)abstract
- A novel fusion assay was established to determine fusion activity with cocultivated human foreskin fibroblasts of stable transfectants derived from human astrocytoma cells (U373) expressing authentic or mutagenized human cytomegalovirus glycoprotein B (HCMV gB; gpUL55). Compared to transfectants expressing authentic HCMV gB, those expressing gB forms with a deletion of hydrophobic domain 1 (hd1; aa 714-747) or with deletions of specific segments in the cytoplasmic tail (aa 811-825 and 871-906) exhibited significantly reduced heterologous fusogenicity. HCMV gB-specific monoclonal antibodies (MAbs) as well as MAb against cellular annexin II prevented fusion of the transfectant expressing authentic gB. Comparable surface exposure of HCMV gB or its derivatives was demonstrated in all transfectants by FAGS analysis. Our observations are compatible with the notion that indigenous fusion activity of HCMV gB depends on the extracellular hd1 domain and on the conformation of the cytoplasmic tail.
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